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Senior Science
HSC Course
Stage 6
Lifestyle chemistry
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P0025971
Number: 43168
Title: Lifestyle chemistry
This publication is copyright New South Wales Department of Education and Training (DET), however it may contain
material from other sources which is not owned by DET. We would like to acknowledge the following people and
organisations whose material has been used:
Cross section of human skin under a microscope, courtesy of Selby-Biolab
Part 3 p 21
All reasonable efforts have been made to obtain copyright permissions. All claims will be settled in good faith.
Published by
Centre for Learning Innovation (CLI)
51 Wentworth Rd
Strathfield NSW 2135
_______________________________________________________________________________________________
_
Copyright of this material is reserved to the Crown in the right of the State of New South Wales. Reproduction or
transmittal in whole, or in part, other than in accordance with provisions of the Copyright Act, is prohibited without the
written authority of the Centre for Learning Innovation (CLI).
© State of New South Wales, Department of Education and Training 2008.
Contents
Module overview ........................................................................ ii
Resources............................................................................................ iii
Icons .....................................................................................................v
Glossary............................................................................................... vi
Part 1: The substances you use..........................................1–39
Part 2: Mixing it up...............................................................1–38
Part 3: Your skin..................................................................1–33
Part 4: What’s growing on your skin? ..................................1–29
Part 5: Dissolve it! ...............................................................1–36
Part 6: Good medicine.........................................................1–40
Student evaluation of module
Introduction
i
Module overview
Welcome to the Lifestyle chemistry module for the HSC component of
the Senior Science course.
If you have ever wondered why some soaps, detergents of cleansers work
better than others then this module will help answer your queries.
You will first study the common substances you use and identify them as
solutions, suspensions or colloids. You might be surprised to find that
many of the substances you use daily are a type of colloid. You will be
involved in the kitchen preparing some tasty foods that are classified as
suspensions and colloids.
This module will enable you to more easily understand the chemistry
behind your soaps and detergents based on their ingredients. As you
learn about the properties of water and alcohol as solvents, you will
inspect the labels of common substances in the home for their ingredients
and the solvents used in them. You will even better understand the
chemistry behind substances that feel warm or cool on your skin.
Despite the use of soaps and detergents you have microbes that live on
your skin. You will understand their role and natural skin acidity in
protecting you against disease through an audiotape or internet audio
files from the www.lmpc.edu.au web site. You will test the pH of a
range of skin and hair products.
You will be asked to test the manufacturer’s claims of a skin or hair
product. You might choose to test different shampoos for claims of
improved body or shine. This experiment will take the form of an
open-ended investigation.
Lastly, you will appreciate different forms of medication such as
capsules, enteric coated and slow release tablets and implants placed
under the skin and relate these to the solubility of the drugs involved.
Enjoy Lifestyle chemistry. Be aware you may find yourself explaining to
people why substances and medications work.
ii
Lifestyle Chemistry
Resources
You will need the following equipment to carry out activities and
experiments during the module. In most cases, you should have most of
the items listed around your home. If not, some items can be made
easily, with little expense.
Part 1
Introduction
•
scissors
•
glue
•
sugar
•
coffee
•
salt
•
milk
•
ingredients and equipment to make:
–
meringues
–
salad dressing
–
mayonnaise
•
flour
•
soil
•
teaspoon
•
two glasses or transparent cups
•
funnel
•
pen-sized laser pointer OR a torch with scissors, cardboard and
rubber band
•
filter paper / paper towel / coffee filters from a supermarket
•
cook books
•
common substances found in the home
iii
Part 2
•
pin or paper clip
•
three waxy leaves
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toothpicks
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a packet of jelly snakes
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a packet of jelly beans or another type of jelly lolly
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detergent
•
oil
•
small jar
Part 3
•
Skin audiotape and tape player or access to www.lmpc.edu.au Skin
audio files
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shampoo label
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soap label
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cleanser label
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light microscope (optional)
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prepared slide of a skin cross section (optional)
Part 4
•
20 cm length of universal pH paper (supplied by teacher)
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coloured pencils
•
eight skin and/or hair products
•
eight cotton buds or ice cream sticks
Part 5
•
six cosmetics and/or medications for external use from home
Part 6
iv
•
vitamin pills label
•
a variety of drug forms – capsules, tablets, enteric coated tablets,
slow-release tablets
•
transparent containers
Lifestyle Chemistry
Icons
The following icons are used within this module. The meaning of each is
written beside it:
The hand icon means there is an activity for you to do.
It may be an experiment or you may make something.
The talk icon guides you to discuss a topic with others.
There are exercises at the end of each part for you to
complete and send to your teacher.
The headphone icon asks you to complete an activity
while listening to an audio file.
The safety glass icon points out that care needs to be taken
when carrying out a task.
There are suggested answers for the following questions at
the end of each part.
Introduction
v
Glossary
The following glossary provides the scientific meaning for many of the
term used in this module, Lifestyle chemistry.
The HSC examiner will expect you to understand the meaning of every
scientific term used. If you find a term that you do not understand, then
look it up in a scientific dictionary or ask your teacher for assistance.
vi
acid
substance capable of forming hydrogen ions when
dissolved in water; substance with a pH below 7
acid mantle
the slightly acid pH of skin, protecting the body
against colonisation by disease-causing organisms
adhesive forces
forces acting between molecules of a substance and
molecules of another substance
alkali
substance which produces an alkaline solution
(containing hydroxide ions) with a pH greater than 7
amino acid
basic unit of protein; a protein is made up of
hundreds or even thousands of amino acid units
apocrine gland
releases sweat which helps with cooling by
evaporation; found alongside coarse hair
bacilli
rod shaped bacteria
bacteria
single celled procaryotic organisms belonging to the
protist kingdom
beading
becoming sphere-shaped
biodegradable
a substance capable of being broken down by the
action of living organisms
capsule
cylinder shape with rounded ends, usually made of
gelatin and in two parts that can be opened
cocci
sphere-shaped bacteria; coccus is one bacterium
cohesive forces
forces acting between molecules of the same
substance eg. hydrogen bonds between water
molecules
colloid
mixtures where large molecules or small clusters of
molecules are dispersed through the liquid and do not
settle out
Lifestyle Chemistry
Introduction
dermal patch
thin medicated strip applied to the skin; delivers
medication to the body through the dermis eg.
nicotine patch
dermis
innermost layer of skin containing sweat glands, heat
sensors, thermoregulators and blood vessels
disperse
to spread out
dissolution
dissolving
dissolving
a solute mixing with a solvent, forming a solution
emulsifier
emulsifying agent eg. soaps, gums, sulfonates,
quaternary ammonia compounds
emulsifying agent
material which makes it possible to stabilise a colloid
or emulsion
emulsion
dispersion of a liquid in another liquid in which it is
immiscible
enteric coated
coated with a stomach acid resistant layer that
dissolves in the alkaline small intestine
enzyme
protein which is a catalyst for a biochemical reaction
such as protein synthesis or hydrolysis of fat
epidermis
outermost layer of skin; protects the underlying
tissue, forms a barrier from heat loss, water loss and
micro-organisms
ethanol
CH3CH2OH colourless liquid alcohol, miscible with
water; produced by yeast fermentation of a sugar
fibroblast
cell which maintains skin elasticity
gall bladder
stores bile to aid the digestion of fats
hair
traps heat on the surface of the skin; insulation layer
hair bulb
site of hair growth
hair follicle
the under skin section of hair
helical
spiral shaped
hydrophobic
water repelling
hydrophilic
attracted to water
hydroxide group
hydrogen atom and oxygen atom joined together
often as a negatively charged ion OH-
immiscible
incapable of mixing to form a solution
keratin
tough protein present in the epidermis of vertebrate
organisms; in hair, feathers, fingernails
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large intestine
part of the alimentary canal (digestive system);
absorbs water from wastes to produce faeces
liver
produces and sends bile to the gall bladder to aid the
digestion of fat
lymph
liquid, mostly water from blood, drained from the
spaces between cells back to the circulatory system
near the heart
melanin
pigment present in skin and hair; its presence or
absence determines colouring of skin and hair
melanocyte
produces and injects melanin into surrounding cells
for skin pigmentation
meniscus
the surface shape of a liquid; dependant on cohesive
forces between molecules and the adhesive forces
between molecules and the container.
methanol
CH3OH colourless liquid alcohol; miscible with
water;
microbes
microscopic single celled organisms
micro-organisms
microscopic single celled organisms
mite
very small arthropod; some are free living; some are
parasitic
mixture
two or more substances not chemically combined
mould
fungal growth
muscle
tissue involved in movement; causes hair to become
erect, trapping warm air close to the surface of the
skin, helping temperature regulation
narcosis
general anesthesia
narcotic
drug producing narcosis
non-polar
molecule with no electric charge; non-ionic
oesophagus
tube connecting the mouth to the stomach
pancreas
produces enzymes which aid digestion of proteins,
lipids and carbohydrates
pathogen
disease-causing organisms
pH
hydrogen ion concentration; pH = - log [H+];
pH scale commonly ranges from 0 to 14; measure of
acidity and alkalinity
polar
a molecule containing an electric charge; ionic
Lifestyle Chemistry
Introduction
polymer
a large molecule made of a chain of monomers with
the same chemical structure
rectum
stores and passes intestinal waste to the exterior
through the anus
sebaceous gland
produces oils to lubricate the hair and skin
sebum
oil produced by sebaceous glands in the dermis
secondary hair
darker, wiry hairs emerging after puberty from vellus
hair follicles
slow-release
designed to provide slow release over time
small intestine
site of digestion and absorption of the products of
digestion
soluble
capable of dissolving
solution
contains dissolved substances that are uniform
throughout, is transparent and may be coloured; the
solute is dissolved entirely in the solvent
solvent
the substance in which a solute dissolves
staphylococci
cocci bacteria appearing in grape-like formations
stomach
site of protein digestion; contains strong acid in
gastric juices
subcutaneous layer
consists of larger connecting veins and arteries and
fatty tissue to help insulate the body
subdermal implant
inserted under the skin to release medication over a
period of time
surfactant
surface active agent with one end of each molecule
capable of dissolving in water and the other capable
of dissolving in oil; substance that lowers the surface
tension of a liquid
suspension
insoluble solids suspended in liquids; the solids
eventually settle upon standing
sweat gland
excretes saline water; releases body heat through
evaporation of sweat (cooling)
synthetic
artificial as opposed to natural; made in a laboratory
or chemical factory
vellus hair
fine, short, fair hair covering the body
yeast
single celled fungus; used in brewing and baking
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Senior Science
HSC course
Stage 6
Lifestyle chemistry
Part 1: The substances you use
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Senior Science Stage 6 HSC Course
Lifestyle Chemistry
•
The substances you use
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Mixing it up
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Your skin
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What’s growing on your skin?
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Dissolve it!
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Good medicine
Medical Technology – Bionics
Information Systems
Option
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Contents
Introduction ............................................................................... 2
Common substances................................................................. 4
Substance use in retail.........................................................................5
Properties of substances .....................................................................6
Mixtures..................................................................................... 8
Solutions, suspensions and colloids....................................................9
Colloid types............................................................................ 16
Colloid classification...........................................................................19
Making colloids and suspensions......................................................21
Summary................................................................................. 23
Appendix 1 .............................................................................. 25
Appendix 2 .............................................................................. 27
Suggested answers................................................................. 29
Exercises – Part 1 ................................................................... 33
Part 1: The substances you use
1
Introduction
At the end of Part 1 you should be able to: classify some common
substances as solutions, suspensions or colloids; make some suspensions,
solutions and colloids and appreciate the wide range of chemicals we
regularly use from food to paint. Be aware that Part 1 should take around
six hours to complete.
In Part 1, you will be given opportunities to learn to:
•
identify that a wide range of substances are used daily as part of our
food, our hygiene, our entertainment and maintenance of our health
•
identify that solutions, colloids and suspensions occur in a wide
range of consumer products
•
explain that mixtures can be
–
solutions that contain dissolved substances and are uniform
throughout
–
suspensions containing particles that settle out, or form layers,
quickly
–
colloids with particles that remain suspended for long periods of
time and include
–
–
liquid-in-liquid (emulsions)
–
oil-in-water
–
water-in-oil
gas-in-liquid (foams)
In Part 1, you will be given opportunities to:
•
2
process and analyse information to identify the range of chemicals
used in every day living including:
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detergent
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lubricant
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pesticide
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solvent
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metal cleaner
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body hygiene chemicals
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cosmetic
and outline any precautions that may be needed in the use and
handling of these chemicals
•
use first-hand or secondary sources to gather, process, analyse and
present information to identify examples of suspensions and colloids
and outline one advantage of a mixture being in each form
•
plan, select appropriate equipment or resources for, and perform a
first-hand investigation to produce a range of suspensions and
colloids that are used by consumers including
–
beaten or whisked eggs
–
salad dressing (oil/ vinegar)
–
mayonnaise
Extract from Senior Science Stage 6 Syllabus © Board of Studies NSW,
October 2002. The most up-to-date version is to be found at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html
Part 1: The substances you use
3
Common substances
A substance is the material of which something consists.
What substances do you use every day? Have you ever wondered what
these substances are made of? Why would you use some things for some
substances and not others? Would you use soap as hair conditioner?
Would you use dishwashing liquid to moisturise your skin? Would you
use window cleaner to wash the family car? Why not? Why are
substances used for specific purposes?
1
List all the substances you use, every day from the time you wake up in
the morning until you go to bed at night. This includes the types of food
you eat, hygiene, entertainment, cleaning and health needs. Don’t be
surprised if you don’t have enough room for your answer!
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Were you surprised with the amount of substances you use each day?
Think about other people and the substances they use each day. They
may use: cosmetics; dental floss; hairspray; shaving cream; perfume or
after shave; vitamins; skin creams; laundry detergents; and cleaning
products.
2
Can you think of any other substances other people use daily?
______________________________________________________
______________________________________________________
Businesses can use quite different substances on a daily basis than you
use. These substances are discussed in the following section.
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Substance use in retail
The following businesses use many different substances. Some of these
are listed below.
1
For each of the following businesses, add two more substances you
assume the business uses regularly. If you are unsure, ask someone for
help.
a) Hair salon
• hair dyes
• hair mousse
• perming solution
• ________________________
• ________________________
b) Cafe
• cooking oil
• disinfectant (for mopping floors)
• detergents (for washing dishes)
• ________________________
• ________________________
c) Service station
• engine oil
• water
• unleaded petrol
• ________________________
• ________________________
Check your answers.
2
Can you think of another retail industry and the substances it uses?
Record your answer below.
•
________________________
•
________________________
•
________________________
•
________________________
•
________________________
Turn to Exercise 1.1 at the back of this part to identify a range of common
chemicals used in everyday living.
Part 1: The substances you use
5
Properties of substances
A property is a characteristic or feature of something. Can you suggest a
property of a chemical? Some properties of a chemical are: state of
matter (solid, liquid, gas); colour; density; melting point; reaction with
oxygen; reaction with acid and so on.
The properties of a chemical depend on:
•
the particles that make up the chemical
•
how the particles are arranged
•
the forces (interactions) between the particles.
There are two main types of properties of chemicals – physical properties
and chemical properties. A knowledge of these properties is important in
identifying the characteristics of a particular chemical.
Physical properties
A physical property is a property of the substance by itself. For example:
•
state of matter
•
colour
•
density
•
how it feels to touch
•
odour
•
taste.
Sometimes you rely on the physical properties of a substance for its use.
You wouldn’t wear perfume or after shave unless it had the physical
property of odour. You eat certain foods for their taste. You choose
particular paint for its physical colour properties.
Write down the physical properties of two other substances you use.
_________________________________________________________
_________________________________________________________
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Chemical properties
A chemical property is a property of the substance reacting with another
chemical. Chemical properties are what we observe when a substance
reacts with another chemical.
You have probably heard of elements, compounds and mixtures. Briefly,
elements are made up of only one type of atom. Pure gold is an example
of an element, containing only gold atoms. Compounds contain more
then one type of atom joined together. Water (H2O) is an example of a
compound as it contains two hydrogen atoms and one oxygen atom
joined together. Mixtures contain different substances not chemically
combined. Mixtures can often be separated by a process based on the
physical properties of the compounds.
This module focuses on mixtures. You use mixtures each time you wash
your face, brush your teeth, drink soft drink, bake a cake, moisturise your
skin and the list goes on.
Sometimes you rely on the chemical properties of a substance to achieve
a desired outcome. Examples are:
•
cake mixture changes from a liquid to a solid when baked
•
some paint strippers react chemically with paint to remove it
•
hair dye reacts chemically with hair and oxygen to colour the hair.
Chemical reactions are often very difficult to reverse. For example a
cake cannot be unbaked and the milk and flour separated.
Sometimes we rely on both the physical and chemical properties of a
substance. The hair dye example has important chemical properties,
however the resultant physical property of colour is also important.
Can you think another example of a substance you use due to its chemical
properties?
_________________________________________________________
Part 1: The substances you use
7
Mixtures
Mixtures consist of more than one substance. Air is a mixture of gases
such as oxygen, nitrogen, carbon dioxide and hydrogen. The substances
you use will fall into three categories.
1
2
Use the code table below to determine the three types of mixtures.
a) solutions
_______________
b) suspensions
________________
c) colloids
_______________
a
b
c
d
e
f
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Do you know what the above terms mean? Refer to the Glossary at
the beginning of this module to define each of the three types of
mixtures, from question 1.
a)
__________________________________________________
__________________________________________________
b)
__________________________________________________
__________________________________________________
c)
__________________________________________________
__________________________________________________
Check your answers.
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Solutions, suspensions and colloids
You might be wondering what solutions, suspensions and colloids are.
Their definitions are listed below.
Solution
Solutions contain dissolved substances that are uniformly spread
throughout the solvent. A true solution is transparent and may be
coloured. The solute is dissolved entirely in the solvent.
Suspension
Insoluble solids suspended in liquids are called suspensions.
The solids eventually settle upon standing.
Colloid
Mixtures where large molecules or small clusters of molecules are
dispersed through the liquid and do not settle out are colloids.
The particles in a colloid have the same electric charge on their surface.
This common electric charge repels the particles from one another and
keeps them dispersed and moving throughout the liquid. The particles
cannot join together to form a particle large enough to settle out. Fine
negatively charged clay particles and charged protein on the surface of
butter fat droplets in milk make fine clay in water and milk colloids. The
protein and nucleic acid molecules floating in the fluid of living cells are
colloids.
The table on the following page outlines the characteristics of each type
of mixture at a glance. You will notice that the particle size; settling of
particles to the bottom of the mixture; residue left after filtering; a light
beam visible in the mixture when shone though the mixture; and the
effect of an electric current or an electric field are all measurable
characteristics that define a mixture as a solution, suspension or colloid.
Part 1: The substances you use
9
Characteristics
Solution
Suspension
Colloid
particles smaller than 10-6 mm
✓
✗
✗
particles larger than 10-3 mm
✗
✓
✗
particles between 10-3 and 10-6 mm
✗
✗
✓
settling of particles
✗
✓
✗
residue left after filtering
✗
✓
✗
a light beam can be seen in the mixture
✗
✓
✓
affected by an electric current or field
✗
✗
✓
You should now be aware of the characteristics that define solutions,
suspensions and colloids
From the table above, record all the characteristics of each mixture type.
Some have been done for you as a guide.
a)
Characteristics that define a solution are:
•
particles smaller than 10-6 mm (0.000001 mm)
•
no settling of particles
•
__________________________________________________
•
__________________________________________________
•
__________________________________________________
__________________________________________________
b) Characteristics that define a suspension are:
•
particles larger than 10-3 mm (0.001 mm) and can be seen under
a light microscope
•
__________________________________________________
•
__________________________________________________
•
__________________________________________________
•
__________________________________________________
__________________________________________________
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c)
Characteristics that define a colloid are:
particles are between 10-3 mm and 10-6 mm (0.001 mm and
0.00001 mm)
•
•
_________________________________________________
•
_________________________________________________
•
_________________________________________________
•
_________________________________________________
_________________________________________________
Check your answers.
You can use the characteristics that define solutions, suspensions and
colloids to determine which of the three categories some common
household substances belong to.
Predict the categories each of the following mixtures, based on your current
knowledge. (The object of this exercise is to start you thinking about the
properties of different substance. This does not mean you have to be right.)
Mixture
Solution/suspension/colloid
a)
sugar in water mixture
_______________________
b)
salt in water mixture
_______________________
c)
milk in water mixture
_______________________
d)
coffee in hot water mixture
_______________________
e)
flour in water mixture
_______________________
f)
soil in water mixture
_______________________
Are you ready to investigate which category those substances actually
belong to? The activity on the following page investigates the
characteristics of each substances above, helping you to identify each
mixture as a solution, suspension or colloid.
Part 1: The substances you use
11
Substance classification
Aim
To investigate the properties of mixtures and use these properties to classify the
mixtures as solutions, suspensions or colloids.
Apparatus
You will need to collect:
•
teaspoon
•
filter paper or paper towel or
coffee filters from supermarket
•
sugar
•
salt
•
two glasses or transparent cups
•
milk
•
funnel
•
coffee
•
•
flour
•
soil
pen-sized laser pointer (these
are class 1 or 2 lasers with a
power output of < 1 milliwatt)
OR a torch with scissors,
cardboard and rubber band
Method (best at night in a room which can be darkened)
You can use the pen sized laser pointer as your light source but
DON’T LOOK DIRECTLY AT THE LASER LIGHT BEAM.
If a laser pointer is not available prepare a torch as shown in steps 1 to 5.
torch face
cardboard
1
Place your torch face down on a
piece of cardboard and trace
around the torch face.
2
Draw a second circle outside the
first circle from step 1.
3
Cut around the larger circle.
Place a hole in the centre using a
pen.
4
Cut inwards towards the centre
circle to create tabs.
hole
12
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5
cardboard
torch
hole
rubber band
beam of light
Fold the tabs and place the
cardboard over the torch face,
securing it with a rubber band as
shown. When the torch is on, a
beam of light should come
through the hole in the
cardboard.
Record your observations in the table on page 12 as you work through
the method:
6
Place a teaspoon of sugar in half a glass of water and stir twenty
times. This prepares a mixture of about 1% concentration.
7
Shine the beam of light through the sugar solution. Looking from
the side can you see the light beam in the solution?
8
If you have round filter paper,
fold it in half as shown in the
diagram. If you are using
paper towel, cut it into a circle
shape with minimum diameter
of 15 cm, then fold it in half.
A coffee filter can be placed
over the top of a glass or cup.
9
Fold the filter paper (or paper
towel) in half again, then open
out the paper to form a cone
shape as shown. A coffee
filter is already made in a
cone shape.
10 Place the filter paper inside the funnel with a glass or cup underneath
to catch the filtered solution. You may need to moisten the funnel
with water to keep the filter paper inside the funnel. You will need a
new piece of filter paper or paper towel to filter each of the mixtures.
11 Filter the first substance by gently pouring the sugar mixture into the
filter paper, not allowing it to fill above the filter paper.
12 Leave the mixture to filter. Do any particles settle out? Is any
residue left on the filter paper?
13 Make and test mixtures: salt with water; milk and water; coffee and
water; flour and water; and soil and water using the mixing
directions from Step 6.
Part 1: The substances you use
13
14 Repeat steps 7-12 with salt mixture, milk mixture, coffee mixture,
flour mixture and soil mixture.
15 Identify each type of mixture as a solution, suspension or colloid.
Results
Record your observations below.
Solute
Light beam
Filtering
Settling
particles
Solution or
suspension
or colloid?
sugar
salt
milk
coffee
flour
soil
1
Look at the characteristics that define a solution, suspension and colloid
(on the previous pages). State which category each mixture belongs in.
Explain your answer based on your results.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
2
Can you give other examples of common solutions, suspensions and
colloids? (Remember they must have all the characteristics of a
solution, suspension or colloid)
a) solutions
__________________________________________________
b) suspensions
__________________________________________________
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c) colloids
_________________________________________________
Check your answers.
How do you think you could tell the difference between a solution,
suspension and a colloid?
•
Solutions appear clear, leave no residue when filtered and a light
beam cannot be seen in the solution.
•
Suspensions contain insoluble solids that will eventually settle,
forming layers upon standing. Residue is left when filtered and a
beam of light can be seen in the suspension.
•
Colloids are mixtures of large molecules or small clusters of
molecules dispersed in a liquid. Colloids are not clear, a beam of
light can be seen in the colloid, and no residue is left after filtering.
If the particles in these mixtures were magnified about one million times
they could look like this:
solution particles
suspension particles
colloid particles
edge of a round
suspension particle
The particles in a solution are much smaller than the wavelength of light.
The particles in a suspension and colloid are larger than or similar in size
to the wavelength of light and can scatter the light showing the beam.
You are about to classify some common substances as solutions,
suspensions and colloids. Use this information to help you classify.
Turn to Exercise 1.2 at the back of this part to classify some common
substances as solutions, suspensions or colloids.
Part 1: The substances you use
15
Colloid types
You already know that colloids are mixtures where the particles between
10–6 and 10–3 mm are dispersed in a liquid and don’t settle out. There are
several types of colloids. The main colloid types you need to study are:
•
solid-in-liquid such as water-based paint, ink, jelly, toothpaste
•
gas-in-liquid foams such as mousse, whipped cream
•
liquid-in-liquid emulsions such as oil-in-water or water-in-oil.
You may be surprised to find that some substances you commonly use fit
into one of these colloidal categories.
Often two different substances don’t mix well and require an
emulsifying agent or emulsifier. The added emulsifying agent produces
a stable dispersion of one liquid in another eg. soap added to oil and
water.
An emulsifier is a surfactant. It coats droplets of liquids eg. oil, causing
them not to stick to other oil molecules, therefore allowing them to be
dispersed through a liquid it is not soluble in directly.
emulsifier
oil
water
oil
Emulsifier stabilising droplets of oil in water
An emulsion is therefore a uniform mixture of two substances that are
normally immiscible. The term immiscible means unable to dissolve in
another substance eg. oil is immiscible in water.
Protein is often used as an emulsifying agent with food oils. In
mayonnaise the protein in egg coats food oil droplets, allowing the oil to
be dispersed through water.
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Detergents are emulsifying agents. They are attracted to the surfaces
between oil and water. As soon as oil is broken up into droplets the
emulsifying agent coats the droplets stopping them from joining together.
This disperses the oil in water rather than leaving oil attached to plates
and cups. The oil droplets do not join because of the emulsifier coating.
Think about oil and water. Oil usually floats on the surface of water.
An oil-in-water colloid has small oil droplets dispersed through water.
An emulsifying agent ensures the droplets are dispersed throughout the
water, at least for a short period of time depending on the properties of
the emulsifying agent.
Gas-in-liquid
Can you think of any substances that are foamy? Many of them are used
in the bathroom. These are all gas-in-liquid colloids.
Examples of gas-in-liquid colloids are:
•
soap suds
•
hair mousse
•
shaving foam
•
beer foam
•
soft drink foam
•
whipped cream.
The foam that forms on the top of beer and soft drink consists of bubbles
of carbon dioxide gas in liquid. As the bubbles burst the gas part is lost
to the air and the liquid part joins the rest of the liquid.
Liquid-in-liquid
A mixture of two liquids where one is dispersed in the other is a liquidin-liquid colloid or emulsion.
Examples of emulsions are:
•
milk
•
mayonnaise
•
coffee and tea with milk
•
cream.
Part 1: The substances you use
17
Two very common types of liquid-in liquid colloids are:
1
Oil-in water colloids such as:
•
water based salad dressings
•
some water-based moisturisers
•
sunscreen
•
milk and cream
2
Water-in-oil colloids such as:
•
oil-based moisturisers
•
oil-based salad dressings
•
butter
A way of distinguishing between oil-in-water and water-in-oil colloids
In an oil-in-water emulsion such as milk the oil droplets are dispersed in
water. If a drop of water soluble dye is added to an oil-in-water emulsion
the dye colour spreads and the emulsion appears the dye colour.
water soluble dye
water
oil
In a water-in-oil emulsion such as butter the water droplets are dispersed
in oil (butter fat in the case of butter). Here the water soluble dye will not
be able to spread its colour throughout the emulsion.
water soluble dye
oil
water
.
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Other ways of distinguishing between the two main types of liquid-inliquid use the temperature feel of skin and electrical conductivity.
Oil-in-water colloids like cold cream feel cold to the skin. Water has a
high capacity for absorbing heat. Heat moves quickly from the skin into
the water and so the oil-in-water cream feels cold. By contrast water-inoil colloids like ointments do not feel cold. The oil does not absorb
much heat from the skin.
Oil-in-water colloids are better electrical conductors than water-in-oil
colloids
Colloid classification
Remember that all water-in-oil emulsions and all oil-in-water emulsions
are also liquid-in-liquid emulsions. For example, milk is a liquid-inliquid emulsion and an oil-in-water emulsion. Butter is a water-in-oil
emulsion and a liquid-in-liquid emulsion
1
Classify the following liquid-in-liquid emulsions as oil-in-water
emulsions or water-in-oil emulsions. To do this, you will have to
determine if the substance consists primarily of oil or water. If the
emulsion is primarily oil it would be a water-in-oil emulsion.
a) milk
__________________________________________________
b) mayonnaise
__________________________________________________
c) coffee or tea with milk
__________________________________________________
2
Use the information on the previous pages to match the products in the
Appendix 1 with the types of colloids below. Cut out the products in the
Appendix 1 and stick them in the appropriate colloid column below.
Part 1: The substances you use
19
Liquid-in-liquid colloid
Oil-in-water
Gas-in-liquid colloid
Water-in-oil
Check your answers.
You will now create your own colloids and suspensions. This is not as
difficult as it sounds. You don’t need complicated scientific equipment
or chemicals. Almost every time you cook something in your kitchen
where at least one ingredient is a liquid eg. milk, oil, melted butter,
water, cream, juice, honey or vinegar, you make a colloid or suspension.
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Making colloids and suspensions
Are you ready to turn your kitchen into a laboratory? Are you a good
cook? You should enjoy eating your results!
Your aim is to produce a range of colloids and suspensions.
Look up recipes for:
•
meringues
•
salad dressing with oil and vinegar
•
mayonnaise
•
smoothies.
Recipes for the foods listed are available in Appendix 2. If you are not
satisfied with these recipes, you may choose to use other recipes from
cook books at home or ask your family and friends for recipes.
Each of these recipes will demonstrate one form of colloid or suspension.
You must:
•
find and record recipes
•
record the equipment and ingredients you will need
•
make the mixtures from the recipes
•
identify the type of colloid or suspension for each mixture.
One of the above recipes will settle out suspended solids if left standing
for a period of time, indicating it is a suspension. State which mixture is
a suspension in your conclusion.
Turn to Exercise 1.3 to plan, carry out and report on your experiment.
Advantages
Why do you put sugar in your tea instead of consuming it separate to the
tea? Why do you mix ingredients together, making a cake rather than
eating them separately? You answers are probably because they taste
better. There are advantages to sugar dissolving in tea, forming a
solution; and making a suspension such as a cake mixture.
What advantages do solutions, suspensions and colloids have?
Part 1: The substances you use
21
List three advantages for each of the following solutions, suspensions and
colloids. It may help you to think about the different products that can be
made in each case eg. suspending sand and gravel in liquid cement helps the
cement become firm when dry.
1
Dissolving sugar in water to form a solution.
______________________________________________________
______________________________________________________
______________________________________________________
2
Suspending solid particles in a liquid to form a suspension.
______________________________________________________
______________________________________________________
______________________________________________________
3
Mixtures of substances being even throughout by forming a colloid.
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
Medicines in suspension form
Some medicines contain fine, undissolved particles suspended in a liquid
base e.g. calamine lotion. The particles settle to the bottom of the
containers after prolonged standing. It is important to shake a suspension
well before use to evenly distribute the drug particles.
Any medicine labeled suspension, lotion or emulsion should be checked
for an instruction to shake well before use.
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Summary
1
Match the following substances with the category it belongs to by
drawing a line from the right column to the left column. You may use
Exercise 1.1 as a guide.
detergent
moisturiser
lubricant
Brasso®
pesticide
dishwashing liquid
solvent
engine oil
metal cleaner
turps
body hygiene chemicals
fungicide
cosmetics
shampoo
2
You are now aware that substances you use regularly are solutions,
colloids or suspensions. Refresh your memory by writing: solutions;
colloids; or suspensions above each of the following definitions.
a) ________________________
Mixtures where particles between 10–6 and 10–3mm are
dispersed through the liquid and do not settle out.
b) ________________________
Insoluble solids suspended in liquids. The solids settle upon
standing. Such substances require shaking before use.
c) ________________________
Mixtures containing dissolved substances that are uniformly
spaced throughout and appear clear. The solute is dissolved
entirely in the solvent.
Part 1: The substances you use
23
3
a) What are three different types of mixtures?
__________________________________________________
b) What are the main types of colloids?
__________________________________________________
__________________________________________________
c) Name two common liquid-in-liquid colloids.
__________________________________________________
__________________________________________________
Check your answers.
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Appendix 1
butter
mayonnaise
milk
skin moisturiser
hair styling
mousse
French dressing
beer
sun protection
cream
Part 1: The substances you use
25
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Appendix 2
Meringue
Ingredients
11/2 cups of castor sugar
1 teaspoon cornflour
2 egg whites
1
1 teaspoon vinegar
4 tablespoons of water
/2 a teaspoon of vanilla
Method
1
Preheat the oven at the lowest possible temperature (80–100°C).
2
Place all ingredients in a bowl and beat with an electric mixer until
shiny. This is as far as you need to go to do Exercise 1.3. To make
the cooked meringue continue with steps 3 and 4.
3
Desertspoonfuls of mixture may be placed onto a greased or lined
tray or the mixture may be placed in a piping bag and piped onto a
greased or lined baking tray.
4
Bake in a slow oven for one and a half hours or until dry and crisp.
Salad dressing
Ingredients
1
/2 a cup of vinegar
1
/2 a teaspoon of vanilla
3
/4 of a cup of vegetable oil
1
/2 a teaspoon of mustard
1
/2 a teaspoon of salt
pinch of black pepper
1
/2 a teaspoon of sugar
1 clove of garlic or half a
teaspoon of crushed garlic
Part 1: The substances you use
27
Method
Blend all ingredients with a blender, food processor or hand mixer or
place all ingredients in a jar and shake.
Mayonnaise
Ingredients
11/2 teaspoons of mustard
1 cup of vinegar or lemon juice
400 g can of sweetened
condensed milk
1 teaspoon of salt
1 egg
Method
Beat all together with a whisk, electric beaters or hand blender until well
mixed. It will thicken in the refrigerator.
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Suggested answers
Substance use in retail
1
a) Hair salon: hair spray; hair gel, shampoo and conditioner are
some other substances.
b) Cafe: milk for coffee and tea; and breads, fruit and vegetables
are some other substances.
c) Service station: diesel fuel; and natural gas are some others.
Mixtures
1
a) solutions
b) suspensions
c) colloids
2
a) Solutions contain dissolved substances that are uniformly spread
throughout, are transparent and may be coloured.
b) Mixtures where insoluble solids are suspended in liquids are
suspensions. The solids eventually settle to the bottom upon
standing.
c) Colloids are mixtures of solute and solvent where large
molecules or small clusters of molecules are dispersed through
the liquid and do not settle out.
Solutions, suspensions and colloids
a)
Characteristics that define a solution are:
•
particles smaller than 10-6 mm (0.000001 mm)
•
no settling of particles
•
an electric field has no effect on the solution
•
no residue is left after passing through filter paper
•
a light beam shone through a solution cannot be seen in the
solution.
Part 1: The substances you use
29
b) Characteristics that define a suspension are:
c)
•
particles larger than 10-3 mm (0.001 mm)
•
particles settle out on standing
•
an electric field has no effect on the mixture
•
residue is left after passing through filter paper
•
a light beam can be seen when shone through the mixture.
Characteristics that define a colloid are:
•
particles are between 10-3 mm and 10-6 mm (0.001 mm and
0.00001 mm)
•
particles do not settle out on standing
•
an electric field will cause some particles to move to one
electrode
•
no residue is left after passing through filter paper
•
the path of a light beam can be seen when shone through the
mixture.
Substance classification
1
Sugar and salt in water are solutions because they are both clear,
transparent and leave no residue when filtered. Soil and flour in
water are both suspensions as a layer of solids settles out over a
period of time. Milk in water and coffee in water are typically
colloids as neither will settle out solids over time and no residue is
left after filtering (although this depends on the type of coffee you
used; ground coffee will usually settle out a solid layer indicating it
is a suspension).
2
a) Some common solutions are wine; spirits; and nail polish
remover.
b) Some common suspensions are tea leaves in water; ground
coffee in water; liquid cake mix.
c) Some common colloids are milk; mayonnaise; egg white in
water; and cream.
Classifying colloids
1
a) Milk is an oil-in-water colloid.
b) Mayonnaise is a water-in-oil colloid (the oil-based variety).
c) Coffee or tea with milk are both oil-in-water colloids.
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2
Liquid-in-liquid colloid
Oil-in-water
Gas-in-liquid colloid
Water-in-oil
French
dressing
butter
hair styling mousse
sun protection
cream
skin
moisturizer
beer
milk
mayonnaise
Advantages
1
Dissolving sugar in water can make a drink sweeter, or into a toffee
or a syrup.
2
Advantages of suspending solid particles in a liquid are: small solids
can be used in cosmetics as exfoliants; solid particles in liquids can
provide the basis for coatings such as nail polish; and toothpaste
contains fine solid particles as abrasives to remove plaque from
teeth.
3
Advantages of mixtures that are even throughout are: oils used for
cooking, vitamins and proteins are available to skin in moisturisers;
oil droplets in milk help it taste better; and hair gel contains
substances which help hair styling.
Part 1: The substances you use
31
Summary
detergent
dishwashing liquid
lubricant
engine oil
pesticide
fungicide
solvent
turps
metal cleaner
Brasso®
body hygiene chemicals
shampoo
cosmetics
moisturiser
2
a) Mixtures where particles between 10–6 and 10–3mm are
dispersed through the liquid and do not settle out.
b) Suspensions are insoluble solids suspended in liquids. The
solids settle upon standing. Such substances require shaking
before use.
c) Solutions are mixtures containing dissolved substances that are
uniformly spread throughout and appear clear. The solute is
dissolved entirely in the solvent.
3
a)
Three types of mixtures are solutions, suspensions and colloids
b) The main types of colloids are gas-in-liquid; liquid-in-liquid;
solid-in-liquid.
c) Two colloid types that are liquid-in-liquid colloids are: oil-inwater and water-in-oil emulsions.
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Exercises - Part 1
Exercises 1.1 to 1.3
Name: _________________________________
Exercise 1.1
Are you ready to investigate the chemicals behind the substances you
commonly use?
Look for examples of the following substances in your home. If you
cannot find all of these substances at home, are you able to visit a cousin,
friend or neighbour? Perhaps a visit to your local supermarket might be
quicker.
In this task you must observe the labels for ingredients and safety
precautions for each of the eight substances listed in the table on the
following page.
You need to record:
•
the trade name eg. Sunlight“ dishwashing liquid
•
the number of different chemicals listed in the substance. (Count the
ingredients from the label)
•
record the main ingredient (the first one on the ingredients list) or the
active ingredient(s)
•
precautions required for handling the substance.
Some items may have only an active ingredient on the label, others may
have no ingredients listed. Do your best to fill the entire table on the
following page, then answer the questions that follow.
Part 1: The substances you use
33
Substance
detergent
lubricant
Examples
Trade name
Number of
chemicals
listed
Main
ingredient
Active
ingredient
Precautions
for use
dishwashing
or laundry
detergent
(without
enzymes)
Vaseline or
engine oil
solvent
pesticide
fungicides
nail polish
remover or
turps
cosmetics
body hygiene
chemicals
metal
cleaner
Brasso® or
silver cleaner
34
shampoo,
soap or
deodorants
moisturiser,
foundation, or
lipstick
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1
What substances appear to contain the greatest number of
ingredients?
_____________________________________________________
_____________________________________________________
2
Which substances have detailed precautions for use?
_____________________________________________________
_____________________________________________________
3
Choose two substances with safety precautions listed on the label.
What effect could these substances have if the precautions were not
followed?
_____________________________________________________
_____________________________________________________
_____________________________________________________
Exercise 1.2
Are you ready to classify some common substances as solutions,
suspensions or colloids? You may refer to the information on pages 9 to
15 to help you determine which classification each substance belongs in.
You are to:
•
find, observe and classify six of the following substances: soft drink;
shaving foam; nail polish remover; nail polish; turps, deodorant or
antiperspirant; after shave or perfume; paint; moisturiser; and hair
conditioner
•
observe and classify two other items at home as solutions,
suspensions and colloids.
If you cannot find these substances at home, can you visit a supermarket,
cousin, friend or neighbour?
An example is provided on the following page as a guide.
Part 1: The substances you use
35
Substance and
trade name
Observations
Solution,
suspension or
colloid
orange juice
•
not clear
suspension
•
can see a beam of light in substance
•
particles have settled to the bottom,
forming a layer
Today’s Fresh®
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Exercise 1.3
Normally you do not taste chemicals or mixtures of chemicals. However
when you use Appendix 2 you make colloids and suspensions that you
can taste. Plan and carry out your tasty experiments on making colloids
and suspensions.
Aim
State what are you trying to do.
_________________________________________________________
_________________________________________________________
Apparatus
Ingredients
Equipment required
salad dressing
mayonnaise
meringue
Recipe
Record the equipment and ingredients you will require while making the
three recipes below. Appendix 2 contains recipes for each. If you use an
alternative recipe indicate the different ingredients and equipment.
Part 1: The substances you use
37
Method
Record, or stick in copies of each recipe. If your recipes are larger than
the spaces provided, you may copy them onto sheets of paper, fold them
and stick them in the spaces below.
Meringue
Mayonnaise
Salad dressing
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Results
Classify each mixture prepared as a:
•
suspension or
•
colloid:
–
gas-in-liquid
–
liquid-in-liquid
–
solid-in-liquid
Recipe
Suspension or colloid classification
meringue mix before
cooking
meringue mix after
cooking
mayonnaise
salad dressing
You may wish to take photos of your creations and attach them with this
exercise.
Conclusion
Use the criteria of colloids and suspensions to explain why each recipe
mixture is classified as you indicated above.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Part 1: The substances you use
39
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Senior Science
HSC course
Stage 6
Lifestyle chemistry
Part 2: Mixing it up
0
20
I
er
b
to T S
c
O EN
g
in D M
t
a
r EN
o
p
or AM
c
n
2
Senior Science Stage 6 HSC Course
Lifestyle Chemistry
•
The substances you use
•
Mixing it up
•
Your skin
•
What’s growing on your skin?
•
Dissolve it!
•
Good medicine
Medical Technology – Bionics
Information Systems
Option
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Contents
Introduction ............................................................................... 2
Surface tension ......................................................................... 4
Walking on water..................................................................................5
Water drops on leaves .........................................................................6
Why are water drops spheres?............................................................6
Optional activity ....................................................................................9
Water under gravity............................................................................11
Menisci................................................................................................11
Surfactants .............................................................................. 13
Use or surfactants ..............................................................................14
Emulsions................................................................................ 17
Emulsifiers ..........................................................................................19
Emulsion types ...................................................................................21
Biodegradability....................................................................... 22
Soaps and detergents........................................................................23
Summary................................................................................. 24
Appendix 1 .............................................................................. 25
Appendix 2 .............................................................................. 27
Suggested answers................................................................. 29
Exercises – Part 2 ................................................................... 33
Part 2: Mixing it up
1
Introduction
If you have ever wondered why water beads on polished cars; how some
insects walk on water; why detergents clean grease off plates; and what is
really meant by ‘biodegradable’, you will find out in Part 2. Don’t be
surprised to find the reasons why substances you use, do what they do.
In Part 2, you will be given opportunities to learn to:
•
explain surface tension in terms of the forces experienced by
particles at the surface of a liquid
•
describe surfactants as substances that affect the surface tension of a
liquid
•
state the relationship between the properties of an emulsion and the
types of molecules present
•
outline the purpose of the emulsifying agent in a range of consumer
cleaning products
•
identify that soaps and detergents are emulsifying agents and
surfactants
•
explain why cleaning agents must be surfactants and emulsifiers
•
define the term biodegradable
•
discuss the biodegradability of soaps and soapless detergents
In Part 2, you will be given opportunities to:
•
2
perform first-hand investigations to demonstrate the effect of surface
tension and:
–
the shape of liquid drops
–
the formation of menisci
–
the ability of some insects to walk on water
•
process and present diagrammatic information to describe the effects
of soaps, skin cleansers and shampoos on the solubility of oil
•
perform a first-hand investigation to prepare an emulsion and
compare its properties to those of a solution and suspension
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•
plan, choose equipment or resources for, and perform a first-hand
investigation to gather information about the properties of different
emulsions and use available evidence to compare those properties
Extract from Senior Science Stage 6 Syllabus © Board of Studies NSW,
October 2002. The most up-to-date version is to be found at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html
Part 2: Mixing it up
3
Surface tension
Water molecules are strongly attracted to each other. Water molecules
on the surface of water are strongly attracted to the surrounding surface
molecules and the molecules beneath the surface. This strong attraction
causes the surface of the water to resist attempts to increase its surface
area, thus allowing objects denser than water to sit on the surface. This is
a physical property of water. Refer to the diagram below.
the water molecules
are strongly attracted
to each other
pin
force due to gravity
Surface tension resists the gravitational force of the pin.
1
Gently place a metal pin or a paper clip on the surface of a glass of
water. Try not to break the water surface with your fingers. Keep
trying until you float the pin or paper clip on the water surface.
If your pin or paper clip sinks, try again with another dry pin. Don’t
use pins with a pearl end as these tend to break the water surface and
sink.
Use the above information to explain why a pin, which is clearly denser than
water, is able to float on the surface of water.
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
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Walking on water
Water spiders rely on surface tension for mobility. They literally walk
on water.
Do you live near a waterway, lake, dam or other still water body? If so, you
are able to observe the ability of some insects to walk on water.
Aim
To observe the variety of organisms that can walk on water.
Method
Go to your nearest water body. Walk along the edge of the water body,
observing the insects that walk on water. Walk slowly so as not to
disturb the insects. Record the number of different species you observe
walking on water over a fifteen minute period.
Results
Make a tally of the different species of insects walking on water.
_________________________________________________________
_________________________________________________________
Record the total number of species observed walking on water.
_________________________________________________________
_________________________________________________________
Conclusion
Fill in the blanks below. For example, ‘Six different species were
observed walking on water in the Darling River water course.’
___________ different species were observed walking on water in the
_________________________ water body/course.
Part 2: Mixing it up
5
Water drops on leaves
Go outside and try to collect three waxy leaves.
Use whatever method you can to place a single drop of water on the waxy
surface of each leaf – but be careful – the water may roll off. Draw what
each drop looks like on the leaf surface on the following page.
leaf 1
leaf 2
leaf 3
Cross sections of leaves
1
What was the general shape of the water on the leaves?
_____________________________________________________
2
Can you explain why the water formed that shape?
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answers.
Why are water drops spheres?
Each molecule of water is attracted to the surrounding molecules from
above, below and either side. On the surface of water, water molecules
are attracted only to the molecules on each side and underneath. Water
molecules on the surface are constantly being pulled towards the centre.
For this reason water drops tend to form a sphere, reducing its surface
area as much as possible.
A two dimensional analogy may help you understand the behaviour of
water drops. Imagine a president with twenty security guards.
The security guards surround the president to protect him. Each security
guard tries to stay close to other security guards. This represents the
forces of attraction between water molecules. The security guards don’t
want to expose the president to an assassin. For this reason they will try
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to reduce the surface area exposed to assassins as much as possible,
making a circle around the president. Water drops reduce their surface
area as much as possible, simply because the forces between the water
molecules in the drop of water are so strong – just like the forces between
the security guards and the president.
Modelling a water drop
You are about to make a model showing the internal forces of a water drop.
For this activity you will need:
•
toothpicks
•
jelly snakes
•
jelly lollies such as jellybeans or jelly babies
1
Break seven toothpicks into three even pieces. Each piece should be
about 2 cm long.
2
Cut four snakes into three pieces each. Each piece should be about
4-5 cm long.
3
Collect six jelly lollies. (For the rest of this experiment, jelly lollies
will be referred to as jellybeans because jellybeans were used for the
illustrations. If you chose jelly babies, wild raspberries or another
type of jelly lolly, these replace jellybeans throughout the
experiment.)
4
Stick three toothpick pieces into a jelly bean. Each toothpick piece
should be half sunk into the jelly bean and half sticking out. Refer to
the diagram below which represents steps 4, 5 and 6.
5
Stick a piece of snake end-on onto the toothpicks attached to each
jelly lolly. Refer to the diagram below, which also includes step 6.
6
Stick three more toothpick
pieces on each end of the
snake pieces as shown. Half of
each toothpick piece should be
showing.
A jellybean represents a water molecule (H2O). The snakes
represent the cohesive forces between water molecules. These are
the forces attracting water molecules to other water molecules. The
toothpicks only serve to join the jellybeans and snakes and are to
be ignored in the model.
Part 2: Mixing it up
7
7
Continue steps 4,5 and 6 until
your model resembles the
diagram opposite.
The jellybeans in a row on the previous page represent the water
molecules at the surface of water. The snakes represent the forces
between water molecules on the water surface. The snakes
pointing down represent the cohesive forces between water
molecules on the surface and those beneath the surface.
8
Join the two ends of the chain,
forming a circle. Attach the
five inside snakes to a jelly
bean in the centre as shown in
the diagram opposite.
Forces act between surface molecules and water molecules below
the surface. When there are fewer water molecules beneath the
surface, the surface molecules stick to those fewer molecules,
causing the water surface to become circular. Your model
demonstrates this with only one water molecule in the centre.
In reality, there are thousands of water molecules inside a water
drop, each with the cohesive forces described. In three dimensions,
these cohesive forces cause a small amount of water to become
spherical in shape.
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Explain how your model demonstrates why a water drop is spherical.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Check your answer.
Water drops are three dimensional. Do you want make your model three
dimensional? If so, take the challenge by doing the following optional
activity – but don’t dismantle your model – you will need it for the
following activity. If not, enjoy your model, but save some snakes,
toothpicks and jellybeans for an experiment later in this part.
Optional activity
1 Stick five toothpick pieces into
the centre jelly bean and two
toothpick pieces into the
outside jellybeans each, as
shown in the diagram opposite.
2 Attach a piece of snake to each
of the toothpick pieces from
above.
3 Attach another toothpick piece
to the end of each snake as
shown.
4 Join all the snakes with
jellybeans as shown in the
diagram opposite. (This may
be fiddly – but you can do it!)
Part 2: Mixing it up
9
5 Stick a single toothpick piece
into the five jellybeans from the
previous step. See the
diagram opposite.
6 Attach a piece of snake to each
of the toothpick pieces from
step five. Then attach all five
pieces of snake to a single jelly
bean on top. Your model
should look like the one
opposite.
7 Lastly, attach the top jelly bean
with the one in the center at the
bottom. This is shown in the
diagram opposite.
Congratulations! You just made a three dimensional model showing the
cohesive forces between water molecules. Your model should resemble
half a sphere. If you carried out the same steps on the other side of the
model, it would become a complete sphere. This would resemble a water
drop.
List any problems you had while constructing the three dimensional
model.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Don’t forget to save some snakes, jellybeans and toothpicks for later in
this part.
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Water under gravity
You may be wondering why a water drop from a tap is shaped like a tear
drop instead of a sphere. The answer is gravity.
The force of gravity causes the majority of water molecules to
accumulate towards the bottom of the drop, leaving fewer molecules at
the top. This causes the tear shape.
1
The diagram below shows a spherical water drop. Sketch over the top
of the drop to show the effect of gravity on the drop of water.
Spherical water drop.
2
Explain in your own words why falling water drops appear tear
shaped.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answers.
Other liquids such as oils, liquid mercury, alcohol and many more have
different forces acting between molecules. These forces determine their
surface shape.
Menisci
Have you ever noticed that the surface of water in a glass? The water
surface curves up at the edges. This curved surface is the meniscus
(plural: menisci). The water molecules are attracted to the glass through
adhesive forces. Cohesive forces between water molecules cause them
to ‘stick’ together.
Part 2: Mixing it up
11
The water prefers to ‘stick’ to the glass surface, however these water
molecules still attract other water molecules. The water molecules try to
adhere to more of the glass surface, thus moving up the side of the glass.
Other water molecules are attracted to these molecules and move with
them. Gravitational forces will only allow the water to move a short
distance. The result is the meniscus you see in a glass of water.
The diagram below shows a meniscus of water.
meniscus
beaker
water
Meniscus of water.
Turn to Exercise 2.1 at the back of this part to observe menisci.
You may be wondering what all this has to do with Lifestyle chemistry.
The forces acting on the surface of a liquid determine how it can be acted
upon by surfactants.
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Surfactants
Surfactants are molecules that act at the surface of a liquid,
lowering the liquid's surface tension.
Surfactants are shaped like tadpoles. The head is water soluble and the
tail is oil soluble. There are four different types of surfactants:
•
anionic (negatively charged head)
•
cationic (positively charged head)
•
non-ionic (no charge)
•
amphoteric (positive and negative charges depending on the pH of
the liquid).
Use the above information to identify each type of surfactant below.
Surfactant types.
Part 2: Mixing it up
13
Use of surfactants
Agricultural sprays
When you observed a drop of water on a waxy leaf, you should have
noticed the water beading or becoming a ball. If water is used as a
solvent for agricultural sprays, the water is likely to bead and roll off the
leaves with little effect on the plant.
Surfactants are added to the water to minimise its surface tension. The
surfactant molecules get between the water molecules at the surface.
This reduces the attraction between the water molecules so that instead of
having a strong outside layer able to form balls, the water spreads out.
The water spreading over the surface of a waxy leaf coats it with the farm
chemical. Refer to the diagram below.
leaf
Surfactants allowing chemical spray to spread over the surface of a waxy leaf.
Fire fighting
Silv-ex® foam is used to fight fires. The foam reduces the surface
tension of the water it’s mixed with. The foam sticks to the surface of
trees, grasses and other fire fuels, penetrating their surfaces and keeping
them wet, thus reducing the risk of ignition. It also prevents oxygen
from reaching the fuel.
Cleaning
Detergents, soaps, cleansers shampoo and many other cleaning products
are surfactants. Their action is described in the following section.
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Froth floatation
Froth floatation is used in mining. The crushed rock is mixed with water
and aerated from below. The air bubbles rise through the mixture.
The mineral particles are positively charged and readily stick to water
molecules.
When surfactants are added, the mineral particles stick to the negative
surfactants. The surfactant’s tails are more attracted to the air bubbles
(rising through the solution) than to water, thus attaching to air bubbles
and carrying the mineral particles to the surface. This separates the
mineral from its ore. See the diagram below.
froth
air buble
rising through
the liquid
negative
polar head
enlarged
view
metal ions
air pumped through pipes under pressure
Froth floatation of metal ions using air bubbles.
Part 2: Mixing it up
15
Imagine you are a teacher. Your students must learn about the use of
surfactants. Your students have the information on pages 13 and 14.
Write three questions about the use of surfactants. The questions must be
designed in a way that helps the students understand what surfactants do and
why they are used.
1
______________________________________________________
______________________________________________________
2
______________________________________________________
______________________________________________________
______________________________________________________
3
______________________________________________________
______________________________________________________
______________________________________________________
Many surfactants are also used in the home as emulsifiers. The next
section introduces you to the emulsifiers you use every day.
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Emulsions
You have already learnt about liquid-in-liquid colloids. All liquid-inliquid colloids are also emulsions. You may be wondering what the
exact definition of an emulsion is.
An emulsion is a mixture of tiny droplets of one liquid dispersed in
another in which it is immiscible.
Oil and water normally don’t mix, but oil may be emulsified to allow it
to mix with the water.
Emulsification is the process of dispersing a liquid in another liquid
in which it is immiscible as a stable colloidal dispersion.
Certain substances are used as emulsifiers to hold one substance in
another such as oil in water. Most, but not all, surfactants are
emulsifiers.
An emulsifying agent is a substance added to a mixture to stabilise
an emulsion.
The detergents you just learned about as surfactants are also emulsifiers.
However, not all surfactants are good emulsifiers. You have dealt with
surfactants with very polar heads. This means the heads have a charge
on them. Non-ionic surfactants do not have very polar heads. These
slightly polar surfactants do not emulsify well.
Part 2: Mixing it up
17
Oils do not dissolve in water well (they are immiscible). Emulsifiers
stabilise oil broken up into smaller globules when the oil is shaken with
water. The emulsifiers then hold the oil globules in water, preventing
them from forming larger globules or floating to the surface.
After reading the boxed text on the previous page, you should understand
that emulsifiers disperse an immiscible substance and hold it in colloidal
form – that is, dispersed in a liquid. If this seems too technical for you,
the following paragraph using water and oil as an example may help.
Understanding emulsification
If you are finding it difficult to understand the action of emulsification,
the following analogy may help.
Imagine a gang of criminals in a group as a large oil globule. Police are
the emulsifiers. They have the energy to hold one criminal each. A large
number of police surround the gang, separating them into smaller groups.
The police (surfactants) surround the smaller gangs, holding one criminal
each. The smaller gangs (oil globules) are unable to join back together
due to the force of the police (emulsifiers).
1
Can you think of another way to describe the action of emulsifiers?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
You should already know that cleaning agents contain surfactants.
Liquids containing surfactants are more able to wet and cover the surface
of immiscible liquids. Cleaning agents also need to be emulsifiers in
order to allow immiscible substances to be dispersed in colloid form.
2
Why must cleaning agents contain surfactants and emulsifiers?
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
18
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3
In a single paragraph, explain what emulsifiers do and their role in
forming emulsions.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answers.
Emulsifiers
Soaps, cleansers, shampoo and detergents are all emulsifiers. This means
that they all act on the surface of grease and grime to remove it.
You may have observed oil floating on the surface of water. Oil
molecules are not attracted to water and are less dense than water,
causing oil to float as oil slicks. So how do we get greasy dishes clean?
What do you add to water when washing dishes, your hair, skin or face?
You add emulsifiers. Detergents, soaps, cleansers and shampoos have
molecules with polar heads. This means that one end of each emulsifier
is hydrophilic and attracted to water molecules; the other end is
hydrophobic, repelling water, attracting it to oil molecules.
Emulsifiers work on dirty dishes in the ways described below.
1
Detergent is added to warm water. The hydrophilic ends of each
emulsifier are attracted to and dissolve in water.
2
The surface tension of the water is reduced, allowing water to spread
over the surface of the grease on a plate. The hydrophilic ends are
attracted to the water molecules and the non-polar ends are attracted
to oil.
3
The hydrophobic ends of emulsifiers dissolve in the oil, helping
dislodge it from the plate.
4
With some agitation, small globules of oil are lifted away from the
oil on the plate.
5
Emulsifiers surround oil globules, keeping them dispersed,
preventing them from joining up with other oil globules; as like
electric charges repel each other. Some surfactants remain as a thin
layer on the plate surface to help repel oils.
Part 2: Mixing it up
19
Cut out the diagrams and stages in emulsifier use in Appendix 1.
Stick them below in the correct order and with the correct diagram.
Role of emulsifier in detergent
Diagram
Check your answers.
20
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Turn to Exercise 2.2 to model emulsification.
Turn to Exercise 2.3 to prepare an emulsion and compare its properties with
solutions and suspensions.
Cleaning agents
Cleaning agents must be both surfactants and emulsifiers.
Being surfactants they concentrate at surfaces orientating their polar end
in the most polar liquid and their non-polar chain in non-polar liquid.
Being emulsifers, cleaning agents surround the liquid globules, keeping
them dispersed and stopping them from joining up with other globules.
This enables the dispersed globules to be washed away.
Emulsion types
Emulsion types are the colloid types that involve only liquids, that is,
they are liquid-in-liquid colloids. The two most common types of liquidin-liquid colloid are oil-in-water and water-in-oil. If you just completed
Exercise 2.3, you made an oil-in-water emulsion.
In oil-in-water emulsions, emulsifiers act on the oil, dispersing oil
through the water. In water-in-oil emulsions, the emulsifiers act on the
water, dispersing water through the oil.
How do you think you can tell the difference between a water-in-oil and
oil-in-water emulsion? This can be done by looking at the properties of
emulsions.
One way is to try to conduct electricity through each emulsion.
Oil molecules have a greater electrical resistance than aqueous solutions.
Water-in-oil emulsions conduct electricity poorly. Oil-in-water
emulsions conduct electricity much better than water-in-oil emulsions.
The subject of conductivity brings us to the second method of emulsion
identification. Just as water-in-oil emulsions resist conducting
electricity, so too do they resist heat conduction. For this reason waterin-oil emulsions feel relatively warm to touch. Oil-in-water emulsions
conduct heat quite well and feel cold to touch. Cold cream works on this
principal as it conducts heat away from your body where applied.
Part 2: Mixing it up
21
Biodegradability
Have you heard the term, biodegradable? The media and
advertisements often refer to biodegradability. What do you think of
when you hear the term biodegradable? Write your ideas below.
_________________________________________________________
_________________________________________________________
_________________________________________________________
So what does biodegradable really mean? Is the term as green as
marketing makes it appear to be?
Biodegradable means an organic substance capable of being
decomposed by the action of naturally occurring organisms.
Almost all organic substances are biodegradable. However, some
substances can take years to break down, while others take days.
Biodegradable substances often break down in steps forming
intermediates. Some of these intermediates can be harmful or
detrimental to living organisms eg. nonylphenol is suspected to mimic
hormones, disrupting normal hormonal processes in living things.
22
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Soaps and detergents
Read the information in Appendix 2 on soaps and detergents then answer
the questions following questions.
1
Draw a typical soap molecule below.
2
What substances can soap break down to form?
_____________________________________________________
3
Is soap biodegradable?
_____________________________________________________
4
Why was detergent produced?
_____________________________________________________
_____________________________________________________
5
What were first detergents made from?
_____________________________________________________
6
Explain the problem associated with the first detergents.
_____________________________________________________
_____________________________________________________
7
What problem was associated with second generation detergents and
what was the solution?
_____________________________________________________
8
Do the detergents we use today contain phosphates? Explain why or
why not.
_____________________________________________________
_____________________________________________________
9
What detergents do we use today? Are they biodegradable?
_____________________________________________________
_____________________________________________________
Turn to Exercise 2.4 at the back of this part to discuss the biodegradability
of soaps and detergents.
Part 2: Mixing it up
23
Summary
Use the clues below to fill in the missing words. The highlighted column
tells you what you will learn in Part 3.
1
2
3
4
5
6
7
8
9
10
11
12
13
1 surfactants are used in these to
encourage leaf coverage (two
words; 12,6)
2 water repelling
3 water drops are this shape
4 an organic substance capable of
being decomposed by the action of
naturally occurring organisms
5 made by the reaction of a
hydroxide and fat
6 attracted to water
7 the resistance of a liquid’s surface
to being broken (two words; 7,7)
24
8 surfactant with a negatively
charged head
9 molecule acting on the surface of a
liquid, lowering its surface tension
10 incapable of being mixed to form a
homogenous solution
11 a common liquid-in-liquid emulsion
12 mixture of tiny droplets of liquid
dispersed in another in which it is
immiscible
13 a synthetic surfactant and
emulsifier used for cleaning
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Appendix 1
Emulsifiers surround oil globules,
keeping them dispersed,
preventing them from joining up
with other oil globules; as like
electric charges repel each other.
Some surfactants remain on the
plate to help repel oils.
plate
The surface tension of the water
is reduced, allowing water to
spread over the surface of the
grease on a plate. The
hydrophilic ends are attracted to
the water molecules and the nonpolar ends are attracted to oil.
plate
With some agitation, small
globules of oil are lifted away
from the oil on the plate.
grease
plate
Detergent is added to warm
water. The hydrophilic ends of
each emulsifier are attracted to
and dissolve in water.
plate
The hydrophobic ends of
emulsifiers dissolve in the oil,
helping dislodge it from the plate.
grease
plate
Part 2: Mixing it up
25
26
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Appendix 2
Soaps and detergents
The following information has been sourced from:
Laidler, G. 1991. Environmental Chemistry – an Australian Perspective –
Second Edition. Pearson Education Australia.
Soap has been used as a cleaning agent for over 4500 years. A typical
soap would be sodium stearate C17H35COONa (carbon, hydrogen,
oxygen and sodium), shown in the diagram below.
H
C
H
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
O
C
O–Na+
Sodium stearate © Laidler, G. 1991 Environmental Chemistry An Australian
Perspective – Second Edition Pearson Education Australia.
The part of the soap with the long carbon chain is water repelling or
hydrophobic. The charged end of the soap is hydrophilic and attracts
water. The soap works because the carbon chain end of the molecule
dissolves in the grease or dirt, and the ionic end dissolves in the water.
Soap does not function as a cleaning agent in acidic environments.
Soap is made from renewable natural resource and is biodegradable, this
means it can be broken down into simple molecules (CO2, H2O) by
bacteria in the environment.
Detergents were introduced in the 1950s with better cleaning action than
soap. Their synthetic make up differed from soap, which is made from
the action of a hydroxide on a natural fat.
These branched alkyl benzene sulfonate detergents were too slowly
biodegradable, accumulating in lakes, rivers and sewage treatment
works. Such detergents were responsible for frothing and bubbling in
water ways in the 1960s and early 1970s. An example of these detergent
molecules is shown on the following page.
Part 2: Mixing it up
27
O
S O–Na+
CH3 CH CH2 CH CH2 CH CH2 CH
CH3
CH3
CH3
CH3
O
H
H
C C
represents a benzene ring H C
H
C H
C C
H
Branched alkyl benzene sulfonate (ABS) © Laidler, G. 1991 Environmental
Chemistry An Australian Perspective – Second Edition Pearson Education
Australia.
New (second generation) detergents were formulated. The straight chain
carbon molecules were more readily biodegradable. An example is
shown below.
O
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH
CH3
S O–Na+
O
Straight chain alkyl benzene sulfonate (ABS) detergent © Laidler, G. 1991
Environmental Chemistry An Australian Perspective – Second Edition Pearson
Education Australia
These detergents were expensive and phosphates were added to reduce
the expense. The phosphates could hold calcium, magnesium and iron
ions in suspension, preventing a scum from forming.
Disposal of phosphate detergents added a great deal of phosphate to
water courses, causing algal blooms and eutrophication. Third
generation detergents now contain straight chain ABS detergents as the
active ingredient. The bulk is added in the form of sodium carbonate,
sodium perborate, sodium sulfate or sodium metasilicate. They are
biodegradable, taking slightly longer than soap to degrade.
In domestic detergents, the surfactant molecules carry a negative charge
and are called ionic surfactants eg. alkyl benzene sulfonate. Surfactant
molecules can also be made with a positive charge. These surfactants are
more expensive, but are antibacterial, soften fabric and are therefore used
in nappy rinses and shampoos. Shampoos can also contain non-ionic and
amphoteric surfactants.
Soaps and detergents are emulsifying agents because they stabilise
mixtures of two immiscible substances, such as oil and water, after the
two liquids have been shaken together. Soaps and detergents are also
surfactants (surface active agents) because they have a hydrophilic part
and a hydrophobic part; this causes them to concentrate at surfaces such
as between water and air or between water and oil.
28
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Suggested answers
Surface tension
The forces of attraction between the water molecules on the water
surface cause surface area to be minimised. The surface resists any
attempts to increase its surface area, thereby allowing the pin to float
rather than break the water surface.
Water drops on leaves
1
Water drops are a spherical shape on a leaf’s surface.
2
The water molecules cling together, resisting the waxy leaf.
The outermost water molecules are pulled towards the centre,
therefore reducing the surface area of the water drop, causing a
spherical shape.
Modeling a water drop
The model shows the forces between the surface water molecules and the
water molecules beneath the surface. When less water molecules are
below the surface, the forces between the surface molecules and those
under the surface cause the surface to become spherical. (Other answers
are acceptable.)
Water under gravity
1
2
Part 2: Mixing it up
Falling water drops appear tear shaped because gravity causes most
of the water molecules to condense towards the bottom of the drop,
leaving fewer molecules at the top. (Other answers are acceptable.)
29
Surfactants
1
anionic
cationic
nonionic
amphoteric
Emulsifiers
Role of surfactant in detergent
Diagram
Detergent is added to warm water.
The hydrophilic ends of each emulsifier
are attracted to and dissolve in water.
grease
plate
The surface tension of the water is
reduced, allowing water to spread over
the surface of the grease on a plate.
The hydrophilic ends are attracted to
the water molecules and the non-polar
ends are attracted to oil.
grease
plate
The hydrophobic ends of emulsifiers
dissolve in the oil, helping dislodge it
from the plate.
plate
With some agitation, small globules of
oil are lifted away from the oil on the
plate.
plate
Emulsifiers surround oil globules,
keeping them dispersed, preventing
them from joining up with other oil
globules; as like electric charges repel
each other. Some surfactants remain
on the plate to help repel oils.
30
plate
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Understanding emulsification
1
An example analogy is: a group of star wars fighter craft represent
oil. They are attacked and broken up by enemy fighters. The enemy
fighters represent emulsifiers. The enemy surround small groups of
star wars fighters, preventing them from forming a group. The star
wars fighter crafts are effectively emulsified.
2
Cleaning agents must be surfactants to wet surfaces for dirt and
grease removal. They must also be emulsifiers to keep dirt and
grease from re-accumulating and re-coating surfaces.
3
Emulsifiers for example break up immiscible substances into smaller
globules and hold the globules in suspension in another liquid.
Soaps and detergents
H
1
C
H
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
O
C
O–Na+
Soap molecule.
2
Soap can break down to form CO2 and H2O.
3
Soap is biodegradable, breaking down within several days.
4
Detergent was produced to clean more thoroughly and function in
acidic environments.
5
The first detergents were made from alkyl benzene sulfonates.
6
The first detergents were too slowly biodegradable in the
environment.
7
Second generation detergents were costly. Adding phosphates
reduced the amount required for cleaning.
8
Today’s detergents do not contain phosphates because phosphates
added nutrient to water courses, causing algal blooms.
9
Today’s detergents are straight chain alkyl benzene sulfonates (ABS)
which are biodegradable, taking slightly longer than soap to break
down.
Summary
Answers provided on the following page.
Summary
Part 2: Mixing it up
31
1
A
4
6
H
G
B
R
I
32
C
U
L
T
U
R
A
L
S
P
R
A
Y
S
2
H
Y
D
R
O
P
H
O
B
I
C
3
S
P
H
E
R
I
C
A
L
O
D
E
G
R
A
D
A
B
L
E
5
S
O
A
P
S
I
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T
Y
D
R
O
P
H
I
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I
C
7
S
U
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F
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T
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N
8
A
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I
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N
I
C
9
S
U
R
F
A
C
T
A
N
I
M
M
I
S
C
I
B
L
E
11
M
I
L
K
N
10
13
I
D
12
E
M
U
L
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T
E
R
G
E
N
T
N
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Exercises - Part 2
Exercises 2.1 to 2.4
Name: _________________________________
Exercise 2.1
1
Observe a small amount of water in a small drinking glass. Draw
and label the glass and the meniscus below.
2
Pour a small amount of oil in a small, dry glass. Draw and label the
glass and the meniscus below.
Refer to the Science Resource Book if you are unsure how to draw
equipment scientifically.
This exercise continues on the next page.
Part 2: Mixing it up
33
3
Compare the strength of the adhesive force between water and glass
with the strength of the adhesive force between oil and glass.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
4
Justify the conclusion that the adhesive forces between water and
glass are stronger than the cohesive forces between water molecules.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Exercise 2.2
You should have jellybeans, snakes and toothpicks left over from a previous
experiment.
You will need:
•
2 snakes cut up into approximately 1 cm pieces (16 pieces in total)
•
4 jelly beans
•
16 toothpicks.
Follow the following steps to carry out the activity.
1
Draw a negative symbol “-” at one end of each of the 16 toothpicks.
The toothpicks represent anionic surfactants or emulsifiers with a
negative polar head.
Negative polar heads are attracted to water. The 16 pieces of snake
represent water molecules.
2
Stick a piece of snake on the polar (negative) end of each toothpick.
The result should be 16 surfactants (toothpicks) with their negative
polar heads buried in water (pieces of snake).
Draw one toothpick and snake pieces at this stage. Label the
toothpick as an emulsifier and the snake pieces as water molecules.
34
Part 2 Lifestyle chemistry
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3
Line up the four jellybeans end to end in a row. Their ends should
be touching. This represents oil smeared on a plate.
Draw your jelly beans below. Label them as an oil slick.
4
The non-polar end of each emulsifier is attracted to oil. Stick the
non-polar end of a toothpick into a jellybean. Repeat this with the
other three jellybeans.
The result should be four toothpicks (emulsifiers) with their polar
heads buried in pieces of snake (water) and their non-polar tails
buried in jelly beans (oil). The jelly beans should be arranged the
same as in step 3.
Draw your model at this stage (you should have used only four of
your sixteen toothpicks).
Imagine you agitate the oil, just as you do as you wash up dishes.
The agitation allows emulsifiers to surround the oil, breaking it into
oil globules.
Part 2: Mixing it up
35
5
Each jellybean represents an oil globule. Separate the four jelly
beans, sticking four toothpicks into each jellybean. Each oil globule
should be surrounded with toothpicks (emulsifiers).
If you have ever played with magnets, you will know that two negative
ends repel each other. This is exactly what happens to the negatively
charged heads of emulsifiers. The repelling action prevents the
surfactants from sticking together. For this reason, the oil globules they
are holding are unable to join together.
It is the repelling quality of charged emulsifiers that make them capable
of holding immiscible substances in suspension eg. oil in water.
6
On the diagram below:
•
label the toothpicks as emulsifiers, the jelly beans as oil globules
and the snake pieces as water
•
draw the negative charges where they belong on one end of each
toothpicks (emulsifiers)
•
draw the repelling forces between the negative ends of
toothpicks (emulsifiers). Zig-zag lines might represent this well.
Model representing emulsified oil.
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Exercise 2.3
You will now make your own emulsion.
Half fill a glass jar with warm water. Place a small amount of any oil in
the water and a small amount of detergent. Place the lid on the jar and
shake. You have just made an emulsion.
Tiny oil globules are held inside the liquid by the action of the
emulsifiers in the detergent.
Test the oil-in-water emulsion for the characteristics listed in the table
below. If the characteristic is present ÷ the box. If the characteristic is
not present ¥ the box. You may need to make similar observations to
those made in Exercise 1.2.
Characteristic
Solution
Suspension
settling of particles
¥
÷
residue is left after filtering
¥
÷
light beam shone through the
mixture seen in the mixture
¥
÷
1
Oil-in-water
emulsion
How did you determine if particles did or did not settle in the
oil-in-water emulsion?
_____________________________________________________
2
How did you determine if residue was left after filtering?
_____________________________________________________
3
How did you determine if a light beam could be seen in the
emulsion?
_____________________________________________________
4
Explain the different properties of a solution, a suspension and an
emulsion by using the information in the table above.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 2: Mixing it up
37
5
Refer to Part 1 and compare the properties of a colloid with those of
the emulsion in your table. Were they the same? Finish the
following sentence:
An oil in water emulsion is a ____________
Exercise 2.4
Read through Appendix 2 before attempting this exercise.
Compare the biodegradability of soaps to first, second and third
generation detergents. Present your answer as a scientific discussion.
(Use present or past tense language.)
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
38
Part 2 Lifestyle chemistry
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Senior Science
HSC course
Stage 6
Lifestyle chemistry
Part 3: Your skin
0
20
I
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to T S
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in D M
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Senior Science Stage 6 HSC Course
Lifestyle Chemistry
•
The substances you use
•
Mixing it up
•
Your skin
•
What’s growing on your skin?
•
Dissolve it!
•
Good medicine
Medical Technology – Bionics
Information Systems
Option
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Contents
Introduction ............................................................................... 2
The role of skin.......................................................................... 3
Investigating skin..................................................................................6
Hygiene products ...................................................................... 8
Open–ended investigation....................................................... 11
Summary................................................................................. 14
Appendix 1 .............................................................................. 17
Appendix 2 .............................................................................. 19
Appendix 3 .............................................................................. 21
Appendix 4 .............................................................................. 23
Suggested answers................................................................. 25
Exercises – Part 3 ................................................................... 29
Part 3: Your skin
1
Introduction
In Part 3 you will be given the opportunity to identify the three main
roles of skin, identify the parts of the skin and the common components
of products used on the skin.
In Part 3 you will be given opportunities to learn to:
•
•
identify the role of the skin as
–
an organ to separate the body from the external environment
–
an organ assisting in body temperature control
–
an organ to protect against entry by disease-causing organisms
identify and explain the use of common components of body soaps,
cleansers and shampoos and the reason for their use
In Part 3 you will be given opportunities to:
•
perform a first-hand investigation to examine prepared slides of
human skin
•
identify data sources, plan, choose equipment or resources for, and
perform a first-hand investigation to test a manufacturers’ claim(s)
on a commercial product such as soap, shampoo or shower gel and
use the available evidence to analyse the results and discuss the
validity of the claim(s)
Extract from Senior Science Stage 6 Syllabus © Board of Studies NSW,
October 2002. The most up-to-date version is to be found at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html
2
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The role of skin
The skin is the largest organ in your body. It covers you from head to
toe. Have you ever been frustrated with your skin’s appearance: pimples,
freckles, tan, lack of tan, dryness, stretch marks, sun burn, birth marks
and moles? When you discover the many functions of skin in
maintaining your health, you may feel differently about your skin.
Record as many functions of your skin as you can think of eg. protecting
your body tissues.
_________________________________________________________
_________________________________________________________
_________________________________________________________
The majority of information on skin is delivered on the audio tape Skin.
You are required to listen to each section before carrying out activities on
the following pages.
Listen to the Role of skin section of the Skin audio tape or internet audio files
(at www.lmpc.edu.au, go to Senior Science, go to Lifestyle Chemistry) and
summarise the role of the skin under each of the headings below. (Answers
are not provided to questions 1-3 to encourage you to complete your
summaries.)
1
Barrier
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 3: Your skin
3
2
Protection from disease
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
4
Temperature control
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
5
Listen to the Skin structures section of the Skin audio tape/internet audio
files to correctly label the diagram below.
Cross section of human skin
4
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6
Listen again to the same audio section that you used to label the
diagram on the previous page. Use the information to fill in the
blank spaces in the structure and function table for parts of human
skin below.
Structure
Function
top layers of the skin, protects the underlying tissue; forms a
barrier from heat loss, water loss and micro-organisms
sweat gland
traps heat on the surface of the skin
hair bulb
the under skin section of hair
muscles
dermis
produces and injects melanin into surrounding cells for skin
pigmentation
fibroblasts
subcutaneous
layer
produces oils to lubricate the hair and skin
sweat is released alongside coarse hair to help with
evaporation
Check your answers.
Turn to Exercise 3.1 to explain the three primary functions of the skin.
Part 3: Your skin
5
Investigating skin
Focusing a microscope
Do you remember how to correctly focus a microscope? Appendix 1
outlines the steps involved in focusing a microscope and a labelled
diagram of a light microscope for your review.
You are required to examine a prepared slide of human skin. To do this
you will need to correctly focus a microscope – or at least know how if
you do not have access to a microscope.
Order
Turn to Appendix 2. Cut out the steps involved in focusing a microscope
which appear in an incorrect order. Arrange the steps for focusing a
microscope in the correct order according to Appendix 1 and stick them in
the table below. (If you remember how to focus a microscope, you may not
need to refer to Appendix 1.)
Focusing a microscope
1
2
3
4
5
6
7
8
Check your answers.
6
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Viewing a prepared slide
You are required to examine a prepared slide of human skin.
•
If you have a microscope at home, your teacher may send you a
prepared slide of human skin for you to complete Exercise 3.2a.
•
If you do not have access to a microscope, it is suggested that you
complete Exercise 3.2b. However, it is suggested you view a
prepared slide when on site with your teacher.
Turn to Exercise 3.2a or 3.2b at the back of this part to draw and label a
prepared slide of human skin tissue.
Complete Exercise 3.3, stating the functions of parts identified in
Exercise 3.2.
Part 3: Your skin
7
Hygiene products
How often do you use body soap or shampoo? Do you use a facial
cleanser or do you know someone who does? Are they all emulsifiers?
Do you know what they are made of?
Soaps, shampoos and cleansers all contain emulsifying agents. Their
primary functions are to lift away oils and other contaminants, just as
described in Part 2. However, the components of shampoos, soaps and
cleansers can differ greatly.
General ingredients in shampoos, soaps and cleansers are displayed in
the Appendix 4. You are to compare your shampoo, cleanser and soap
ingredients to those listed in Appendix 4. You will need a list of
ingredients for the shampoo; soap; and cleanser you use at home. If you
do not have these products at home or the package listing the ingredients,
choose a brand of each at the supermarket to complete the following
questions or ask friends or neighbors for help. You will not need to buy
these products. Simply answer the questions based on the labels.
Ingredients are listed from most to least in volume used. If you buy
biscuits with the first ingredient as vegetable oil, you can be assured the
biscuits are fatty. The last ingredient on the ingredients list has the least
volume in the product eg. spices in biscuits. The exception to this is
water.
1
Compare the ingredients of your shampoo with those in the Appendix 4.
Record the ingredients in your shampoo that are the same as those listed
in Appendix 4: Main constituents of shampoo.
_____________________________________________________
_____________________________________________________
2
Use the information in Appendix 4 to state the functions of each of the
ingredients listed above.
_____________________________________________________
_____________________________________________________
_____________________________________________________
8
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3
Did your shampoo contain many other ingredients not listed in the
Appendix 4? Why do you think this is?
_____________________________________________________
_____________________________________________________
Many different substances can do similar things. Companies
producing hygiene products rely on this to create new shampoos
with different qualities. In each instance however, the function of a
shampoo is to emulsify oils and other contaminants, removing them
from the hair and scalp safely with no harmful effects.
4
List the ingredients in a cake of body soap at home.
_____________________________________________________
_____________________________________________________
_____________________________________________________
5
Refer to the Appendix 4: Main constituents of soap to record the
function of the ingredients above.
_____________________________________________________
_____________________________________________________
_____________________________________________________
6
Does your soap contain substances that are not in the Appendix 4?
_____________________________________________________
7
What functions do you think each of these other substances have?
_____________________________________________________
_____________________________________________________
8
List the ingredients in your cleanser that are also listed in the
Appendix 2 under Main constituents of cleansers.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Cleansers often contain many other substances to support claims
such as: antibacterial qualities, make-up removal, deep cleansing,
non-drying, moisturising, exfoliating and many more.
Part 3: Your skin
9
1
List the ingredient(s) that are common to cleansers and shampoos.
_____________________________________________________
2
What are the functions of these ingredients?
______________________________________________________
Soaps act in a similar way to the detergents you outlined above.
They are both emulsifiers.
3
What are the main functions of shampoos, soaps and cleansers?
______________________________________________________
______________________________________________________
Check your answers.
Manufacturers advertise desirable qualities in their hygiene products such
as: extra body shampoos, everyday use shampoos, colour protective
shampoos and pro-v shampoos for improving hair quality. You can
probably think of many more. Cleansers and soap manufacturers make
other claims to help sell their products.
10
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Open-ended investigation
You are required to carry out at least one open-ended investigation
during the HSC Senior Science course. In doing so, you must integrate
and demonstrate skills, knowledge and understanding. This might sound
difficult, but each time you design and carry out an experiment, you are
demonstrating skills and each time you draw conclusions based on your
results and knowledge, you are demonstrating understanding. This
particular open-ended investigation will be fun.
You are about to test the claims of a skin product or a product that comes
in contact with the skin or hair. This investigation is the largest and most
detailed investigation you will plan, carry out and report on in Senior
Science this year. Your teacher may use this open-ended investigation as
an assessment task.
Think about the products in your home. Is there a shampoo that makes a
claim that you have always wanted to test like ‘improved styling’. Have
you always wanted to test those soaps that claim to moisturise your skin?
Does your dishwashing liquid really lift grease well? Do skin firming
moisturisers really make your skin firm?
Can you think of a commercial product such as soap, shampoo or shower
gel, that comes in contact with the skin or hair that you could test? If you
cannot think of any, ask friends and family. You may need to test the
product against another (or several others) to gain results eg. a no-name
soap against Dove® soap; a pro-v shampoo against Pears® shampoo.
Alternative methodology could be for several people or subjects to use
the product. Their observations with regards to the manufacturer’s
claims can form your results.
Your investigation
How you approach, plan and present your investigation is for you to
decide. However, the use of headings such as: aim; apparatus; method;
results; discussion; and conclusion, is strongly recommended as a
framework for your scientific report.
Part 3: Your skin
11
In this section you will only plan your investigation. It is suggested you
plan your investigation in draft first before recording your plan for
Exercise 3.4.
Your plan should be sent to your teacher for review. When your
teacher is satisfied with your plan, you may begin your
investigation.
Your completed open-ended investigation should be handed in with
Part 6, unless another date is specified by your teacher.
Be aware that your teacher may use this open-ended investigation
as an assessment task.
It is essential that you contact your teacher as you complete Part 4 to gain
permission to go ahead with your plan and carry out your investigation.
Remember, you must submit your completed open-ended investigation
with Part 6 unless your teacher specifies a different date.
The time taken to complete the investigation is not included as part of
this module. Your open-ended investigation is homework.
Parts 4, 5 and 6 will contain the following reminder:
?
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
This reminder should prompt you to call your teacher to gain approval to
start your investigation, allowing enough time to complete the
investigation at the conclusion of Part 6.
Ideas to think about
When planning the investigation keep these questions in mind.
12
•
Will you test the product on several people?
•
How long will you need for results to be measurable?
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•
How often will you test the product eg. five times a day or once
only?
•
Will you test several different products and compare their effects?
•
How will you assess if the product does or doesn’t stand up to its
claims; will you record people’s comments on the product use, or
measure results such as relative hair volumes?
•
How will you present your results?
•
Will you graph your results or include photographs?
•
How will you ensure the variables remain constant such as the same
volume of shampoo, the same hair types (ie. straight hair) and the
same amount of rinsing time?
When you complete your discussion and draw your conclusions, will
you:
•
outline your results, relating them to what you have learned about
solutions, colloids, suspensions and emulsions and skin structure
•
relate your results to the ingredients in the substance tested
•
add additional information you have found on similar products
•
suggest improvements to your experimental procedure
•
suggest reasons for the experiment not working
•
suggest further investigations that could be carried out?
When presenting your report, take these suggestions into account.
•
Remember to use scientific language in your investigation.
•
Don’t be afraid to include pictures, diagrams, graphs and tables.
•
Contact your teacher as soon as you need help.
•
Refer to the Science Resource Book or contact your teacher if you’re
not sure how to approach the discussion and conclusion.
•
Enjoy the activity.
Turn to Exercise 3.4 at the back of this part to record your plan for your
open-ended investigation.
Part 3: Your skin
13
Summary
Briefly write what you have learned under each syllabus point below.
Extracts from Senior Science Stage 6 Syllabus © Board of Studies NSW,
originally issued 1999. The most up-to-date version is to be found at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html
•
identify the role of the skin as:
–
an organ to separate the body from the external environment
______________________________________________________
______________________________________________________
______________________________________________________
–
an organ assisting in body temperature control
______________________________________________________
______________________________________________________
______________________________________________________
–
an organ to protect against entry by disease-causing organisms
______________________________________________________
______________________________________________________
______________________________________________________
•
identify and explain the use of common components of body soaps,
cleansers and shampoos and the reason for their use
______________________________________________________
______________________________________________________
______________________________________________________
14
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•
perform a first-hand investigation to examine prepared slides of
human skin. (This section is left blank for you to draw a diagram.)
•
identify data sources, plan, choose equipment or resources for, and
perform a first-hand investigation to test a manufacturers’ claim(s)
on a commercial product such as soap, shampoo or shower gel and
use the available evidence to analyse the results and discuss the
validity of the claim(s).
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 3: Your skin
15
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Appendix 1
Focusing a microscope
eyepiece
tube
nosepiece
objective lens
stage clip
coarse focus knob
stage
condenser
mirror
fine focus knob
condenser adjustment knob
Light microscope.
1
Plug in and turn on a lamp.
2
Face the lamp to the mirror.
3
Turn the nosepiece to set the objective lens on required
magnification eg. x10.
4
Look down the tube through the eyepiece and adjust the mirror to
allow sufficient light through the tube.
5
Place a prepared slide on the stage, clipping it into place with stage
clips.
6
While looking from the side, wind down the tube using the coarse
focus knob till the objective lens is almost touching the slide.
Part 3: Your skin
17
18
7
Look through the eyepiece, down the tube and slowly wind back the
coarse focus knob until the image comes into focus. If an image is
not seen, steps 6 and 7 should be repeated.
8
Adjust the fine focus knob to clearly focus the image.
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Appendix 2
Cut out the following steps involved in focusing a microscope and stick
them in the correct order on page 6.
Adjust the fine focus knob to clearly focus the image.
Turn the nosepiece to set the objective lens on required magnification
eg. x10.
Plug in and turn on a lamp.
Place a prepared slide on the stage, clipping it into place with stage clips.
Look through the eyepiece, down the tube and slowly wind back the coarse
focus knob until the image comes into focus.
While looking from the side, wind down the tube using the coarse focus
knob till the objective lens is almost touching the slide.
Look down the tube through the eyepiece and adjust the mirror to allow
enough light through the tube.
Face the lamp to the mirror.
Part 3: Your skin
19
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Appendix 3
Cross section of human skin as seen under a light microscope.
Magniification x 100 (Scanned from a prepared slide © Selby. Australia.)
Part 3: Your skin
21
22
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Appendix 4
Main constituents of shampoo
Ingredient
Function
methylparaben
preservative
lauramide DEA
foam stabiliser
hydrolysed animal protein
conditioner/stabiliser
propylparaben
preservative
cocamide DEA
foam booster
ammonium lauryl sulfate
detergent
sodium lauryl sulfate
detergent
triethanolamine lauryl sulfate
detergent
propylene glycol
coupling agent
sodium laureth sulfate
detergent
glycol stearate
thickener/pearling agent
hydroypropyl methyl cellulose
thickener
quanternium - 15
conditioner
imidazolidinyl urea
antimicrobial
amphoteric – 2
detergent/conditioner
DMDM hydantoin
antimicrobial
panthenol
vitamin source
© ICI Australia, Chemical Fact Sheets, ICI Australia, Melbourne.
Part 3: Your skin
23
Main constituents of soap
Ingredient
Function
oil (palm oil)
reacts with sodium hydroxide to form soap and
glycerol
sodium hydroxide
reacts with oil to form soap and glycerol
glycerine (glycerol)
formed in the reaction of sodium hydroxide and
oil; thickener
water
used to rinse the soap
sodium chloride
separates glycerol from the soap
fragrance
fragrance
Other substances are present or absent in different soaps to alter texture;
give foaming action; moisturise; have antibacterial qualities; impart
odour; act as abrasives; act as preservatives and many more. Shower
gels and liquid soaps contain similar ingredients to cleansers.
Main constituents of cleansers
Ingredient
Function
water
solvent
sodium lauryl sulfate
detergent
cocamide DEA (and many other
varieties)
foam booster
glycerine
thickener
citric or lactic acid
pH balance
fragrance
fragrance
Other substances are present or absent in different cleansers to alter
texture; give foaming action; moisturise; have antibacterial qualities;
impart odour; act as abrasives and many more.
24
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Suggested answers
The role of skin
5
hair
sebaceous gland opening
opening of
sweat gland
sebaceous
gland
melanocyte
basal layer
epidermis
apocrine
sweat gland
muscle that
pulls on the hair
dermis
hair follicle
hair bulb
subcutaneous
layer
nerve fibre vein
artery
eccrine sweat
gland
Labeled cross section of human skin.
Part 3: Your skin
25
6
26
Structure
Function/s
epidermis
top layers of the skin, protects the underlying
tissue; forms a barrier from heat loss, water
loss and microorganisms
sweat gland
to excrete saline water, releasing body heat
through evaporation of sweat
hair
traps heat on the surface of the skin
hair bulb
site of hair growth
hair follicle
the under skin section of hair
muscles
cause hair to become erect, trapping warm air
close to the surface of the skin, helping
temperature regulation
dermis
middle layer containing skin fibres
melanocyte
produces and injects melanin into surrounding
cells for skin pigmentation
fibroblasts
maintains skin elasticity
subcutaneous layer
consists of larger connecting veins and arteries
and fatty tissue to help insulate the body
sebaceous gland
produces oils to lubricate the hair and skin
apocrine gland
sweat is released alongside coarse hair to help
with evaporation.
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Focusing a microscope
Focusing a microscope
1
Plug in and turn on a lamp.
2
Face the lamp to the mirror
3
Turn the nosepiece to set the objective lens on required
magnification eg. x10.
4
Look down the tube through the eyepiece and adjust the
mirror to allow sufficient light through the tube.
5
Place a prepared slide on the stage, clipping it into place with
stage clips.
6
While looking from the side, wind down the tube using the
coarse focus knob till the objective lens is almost touching
the slide.
7
Look through the eyepiece, down the tube and slowly wind
back the coarse focus knob until the image comes into focus.
If an image is not seen, steps 6 and 7 should be repeated.
8
Adjust the fine focus knob to clearly focus the image.
Hygiene products
1
Ingredients common to cleansers and shampoos are: sodium lauryl
sulfate and cocamide DEA.
2
Sodium lauryl sulfate is a detergent and cocamide DEA is a foam
booster.
3
The main functions of shampoo, soap and detergents are to emulsify
dirt and oils and remove them from the surface of skin or hair.
Part 3: Your skin
27
28
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Exercises - Part 3
Exercises 3.1 to 3.3
Name: _________________________________
Exercise 3.1
There are three main functions of skin. Provide a brief and concise
description of these three functions.
1
_____________________________________________________
_____________________________________________________
_____________________________________________________
2
_____________________________________________________
_____________________________________________________
_____________________________________________________
3
_____________________________________________________
_____________________________________________________
_____________________________________________________
Exercise 3.2
You must complete Exercise 3.2a if you have a microscope or 3.2b if you
do not have access to a microscope. Each activity is outlined on the
following page.
Exercise 3.2a
1
Part 3: Your skin
Focus a prepared slide of a cross–section of human skin tissue on
x100 magnification (this is x10 objective lens combined with the x10
magnification of the eyepiece).
29
2
Clearly draw what you see in the circle below. If you are unsure
how to present your drawing and in what detail, refer to the Science
Resource Book or contact your teacher.
3
Use the labeled diagram of the skin on page 25 to identify and label
your diagram of human skin tissue.
4
Write a title for the diagram and record its magnification next to the
cross on the bottom right corner.
Exercise 3.2b
1
Observe the diagram of a prepared cross–section of human skin
tissue under x100 magnification in Appendix 3.
2
Clearly draw what you see in the circle below. If you are not sure
how to present your drawing, and in what detail, refer to the Science
Resource Book or contact your teacher.
3
Use the labeled diagram of the skin on page 25 to identify and label
your diagram of skin tissue.
4
Write a heading for the diagram and record its magnification next to
the cross on the bottom right corner.
✗
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Exercise 3.3
Each part of human skin has a function. For three labels indicated in
Exercise 3.2, state their functions below.
Part
Function
Exercise 3.4
Plan your open-ended investigation below. You should make a rough
copy on separate paper first. Include attachments with this exercise if
this section is not large enough for your plan.
Keep a copy of your plan for you to follow as you carry out your
experiment over the coming weeks. Perhaps you could keep a
journal.
Aim
What are you trying to find out? What product(s) are you testing?
_________________________________________________________
_________________________________________________________
_________________________________________________________
Part 3: Your skin
31
Apparatus
What and or who will you need to carry out your investigation?
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Method
How will you carry out your investigation? Organise each step
sequentially and either number or dot point the steps. How will you
collect results? Will your data be quantitative (measured) or qualitative
(compared against each other)?
Indicate your dependent and independent variables. Outline how you
will ensure controlled variables are kept constant and what your control
will be. It is essential these points are covered. If you are unsure of these
terms refer to the Science Resource Book or contact your teacher.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
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Results
How will you present your results? Will you use a table? Will you
include photographs or draw a graph? Include a plan showing how you
will record your results. You may include a rough sketch of a graph you
are expecting to draw.
You must indicate if your results are to be quantitative (measured) or
qualitative (compared against each other). If you do not understand the
meaning of these terms, refer to the Science Resource Book or contact
your teacher.
Don’t forget to keep a copy of your plan. You will need to follow
it while conducting your open-ended investigation.
Part 3: Your skin
33
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Senior Science
HSC course
Stage 6
Lifestyle chemistry
Part 4: What’s growing on your skin?
0
20
I
er
b
to T S
c
O EN
g
in D M
t
a
r EN
o
p
or AM
c
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Senior Science Stage 6 HSC Course
Lifestyle Chemistry
•
The substances you use
•
Mixing it up
•
Your skin
•
What’s growing on your skin?
•
Dissolve it!
•
Good medicine
Medical Technology – Bionics
Information Systems
Option
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Contents
Introduction ............................................................................... 2
The microflora of skin ................................................................ 3
Microbe colonisation ............................................................................9
Breaking the barrier............................................................................10
Acidity and alkalinity ................................................................ 11
The pH scale ......................................................................................12
The pH of skin ......................................................................... 14
Skin and hair products .......................................................................16
Testing skin and hair products...........................................................17
Summary................................................................................. 20
Appendix 1 .............................................................................. 21
Appendix 2 .............................................................................. 22
Suggested answers................................................................. 23
Exercises – Part 4 ................................................................... 27
Part 4: What’s growing on your skin?
1
Introduction
Your skin is host to a great number of micro-organisms. They live on
skin oils, proteins and sweat. Your first instinct might be ‘Yuck! Get rid
of them!’ However, these microbes play an important role in body
defence. The skin and hair products you use must be compatible with the
skin’s natural defense or damage and infections can result.
In Part 4, you will be given the opportunities to learn to:
•
define the term microflora and discuss the role of the microflora on
skin in different parts of the body
•
discuss the term pH in terms of its ability to describe the acidity of a
substance
•
explain the relationship between the natural pH of the skin and the
action of
–
microflora
–
natural oil produced by glands in the skin
–
perspiration.
In Part 4, you will be given opportunities to:
•
perform first-hand investigations to measure the pH values of a
range of skin and hair products.
Extract from Senior Science Stage 6 Syllabus © Board of Studies NSW,
October 2002. The most up-to-date version is to be found at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html
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The microflora of skin
The term microflora is an odd term. You should understand the term
‘micro’. It means very small or microscopic in size. You are not able to
see micro-organisms with the naked eye. The second part of the term
microflora is ‘flora’. What would you normally associate the term flora
with? Think about florists, floral patterns, flora and fauna. Have you
decided what flora should mean? Your answer should have been
‘plants’. Automatically your brain should think that microflora means
microscopic plants, right? Wrong!
In this instance, flora appears to take on the meaning of an ecosystem or
a group of organisms surviving together. For this reason, the term
microflora is defined as microorganisms surviving as microscopic
communities.
1
Write the correct definition for microflora in the box below.
Your mouth, nose and ears all contain different varieties of microflora.
Most microflora on and in the body are bacteria. You will be researching
the natural microflora existing on the surface of your skin and what their
effects are.
Part 4: What’s growing on your skin?
3
2
Use the glossary to define the following terms as they will help you
understand the Microflora section of the Skin audio tape/internet
audio files.
bacteria _______________________________________________
______________________________________________________
staphylococci __________________________________________
______________________________________________________
cocci _________________________________________________
______________________________________________________
microbes ______________________________________________
______________________________________________________
micro-organisms ________________________________________
______________________________________________________
sebum ________________________________________________
______________________________________________________
epidermis _____________________________________________
______________________________________________________
keratin ________________________________________________
______________________________________________________
Think about the skin on different parts of your body. Colour the parts of the
body below where you think bacteria might exist. Remember, you are
focusing on where bacteria might exist on the surface of your skin.
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You will see how accurate your predictions were as you listen to the
following audio.
Listen to the Microflora section of the Skin audio tape/internet audio files,
then carry out the activities which follow. You may need to listen to the
tape several times in order to answer all the questions.
3
Why is skin not considered to be uniform?
_____________________________________________________
_____________________________________________________
4
What conditions favour the growth of micro-organisms?
_____________________________________________________
_____________________________________________________
5
All organisms require nutrients to live. What nutrients are available
on the skin surface for micro-organisms to utilise?
_____________________________________________________
6
Why is the skin an unstable site for microbes to colonise?
_____________________________________________________
_____________________________________________________
_____________________________________________________
7
What effects can the action of microflora have on the skin surface?
_____________________________________________________
_____________________________________________________
_____________________________________________________
Appendix 1 contains a species list of microflora found on the surface of
human skin. Use this list to help you spell the species names stated in the
audiotape for the following question.
Word processed genus and species names are italicized
eg. Staphylococcus aureus. The first name is the genus name and must
start with a capital letter. The second name is the species name and
begins with a lower case letter. You might remember from preliminary
work that when hand writing genus and species names, you must
underline each separately eg. Staphylococcus aureus. Do this for the
species column for question 8 on the following page.
Part 4: What’s growing on your skin?
5
8
List the species of microflora in the table below and indicate where
they are commonly found on the body. Disregard the centre column
as you will complete this with question 9. The first one has been
done for you.
Species of microflora
Staphylococcus epidermidis
6
Group
Part of body found
upper body
9
Classify each of the micro-organisms identified above into groups.
The classifications are: bacteria, fungi and mites. Write these names
in the middle column in the above table. All cocci and bacilli are
forms of bacteria. Mould and yeast are forms of fungus. Refer to
Appendix 1 to help you classify each species.
10
Look at the diagrams of cocci, bacilli and moulds on the following
page, then answer the following questions.
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coccus
diplococcus
staphlococcus
Examples of cocci bacteria viewed under a high
powered microscope.
Examples of bacilli bacterium under a high powered
microscope.
Example of a mould under a light microscope (not as
high powered).
10 a) What do the diagrams of cocci bacterium look like to you?
_________________________________________________
_________________________________________________
b) Describe what bacilli look like in one sentence.
_________________________________________________
_________________________________________________
Part 4: What’s growing on your skin?
7
c) Explain the difference between moulds and bacteria when
viewed under a microscope.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
11 For each of the body parts inhabited by microflora in question 8,
indicate the microflora present on the diagram of a person on the
following page.
The places where particular species of microbes are found on human skin.
Check your answers.
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Microbe colonisation
More recent studies have found that microflora of the skin can be divided
into two groups: resident microflora and transient microflora.
Resident microflora are found on the skin surface and are thought to
reside in the sebaceous glands under the skin. Bacterial counts are higher
where more oil is being produced by sebaceous gland activity. Resident
bacteria such as Staphylococcus epidermidis are thought to play an
important role in protecting the individual from more pathogenic or
disease-causing bacteria. It has been found that an area of skin colonized
by relatively harmless bacteria inhibits the growth of other microbes. In
this way, the body is protected from skin diseases and disorders by the
microbes living on the skin surface.
Transient microflora have two sources. The first source is the external
environment eg. soil, water and air. Contact with soil, water and air
transfers any microbes present to the skin surface. The second source is
the natural microflora that comes out of body orifices such as the nasal
passages, ear canals and anus. Micro-organisms are transferred to
various parts of the body by the hands. Once these organisms are
transferred to a suitable site, they can flourish. Transient microbes can
cause diseases such as diarrhoea and meningitis.
Washing with soaps and detergents removes many surface microbes,
along with a great deal of the oily protective layer. However the
remaining resident microbes quickly grow and reproduce to colonise the
‘clean’ skin, restoring the natural microflora of the skin.
Part 4: What’s growing on your skin?
9
Breaking the barrier
Have you ever had a rash or skin irritation? Your skin defence could
have been breached. Have you ever had tinea on your feet? If so, your
skin defence has been breached. There are many ways your skin defense
can be broken. You may have recently broken your skin defense barrier
without realising.
Have you burnt or cut yourself recently? You may have shaved an area
of skin; grazed yourself; or handled chemicals such as turps without
gloves. All these common activities can alter the protective layer of skin.
A change in diet can cause a change in skin acidity, lowering your
defense to harmful micro-organisms. Even washing can remove natural
microflora, allowing more harmful microbes to colonise the area.
Has your skin become damaged over the last two weeks? Record the
damage, how it occurred, the part of the body and any resultant infections or
skin irritations that occurred.
Damage to skin
How the skin
was damaged
Part of the body
Resulting
infections or
irritations
As you have seen, the protective skin barrier is easily damaged. Harmful
microbes living on the skin surface can easily penetrate a wound, causing
an infection.
The use of products that are incompatible with the skin surface can cause
skin damage, alter the natural acidity of the skin or alter the natural
microflora of the skin.
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Acidity and alkalinity
Carry out the following activity to review pH in terms of acidity and
alkalinity.
1
a) Write the numbers 0 to 14 on the scale below.
b) On the line next to ‘7’, after the arrow, write neutral pH.
c) On the line next to ‘1’, write strongly acidic.
d) On the line next to ‘14’, write strongly alkaline.
e) Next to the arrow pointing up, write increasing acidity.
f)
Next to the arrow pointing down, write increasing alkalinity.
0
__________________________________________
14
≠
____________________________________
Æ
____________________________________
Ø
____________________________________
__________________________________________
Well done. You just created a pH scale.
Part 4: What’s growing on your skin?
11
The pH scale measures acidity and alkalinity from 0 to 14. From the
previous activity you should understand that a pH number lower than 7
indicates an acid and a number greater than 7 indicates an alkali. A pH
of 7 is neutral. Most organisms prefer to live in pH neutral conditions (7)
as acids and alkalis tend to damage cells and destroy tissue.
A pH of 4 is more acidic than a pH of 6. A pH of 10 is less alkaline than
a pH of 12. The stronger the acid or alkali, the more dangerous it is as it
has the ability to corrode substances.
0-2 is a strongly acidic; 3-4 is an acid; 5-6 is weakly acidic; 7 is
neutral; 8-9 is weakly alkaline; 10-11 is alkaline; and 12-14 is
strongly alkaline solution.
2
Indicate the acidity or alkalinity of the following pH values using the
above information.
a) 4 _________________________________________________
b) 6 _________________________________________________
c) 13 ________________________________________________
d) 10 ________________________________________________
e) 7 _________________________________________________
f)
9 _________________________________________________
g) 1 _________________________________________________
Check your answers.
The pH scale
You may have received some pH paper from your teacher with this part.
pH paper turns a different colour depending on the acidity or alkalinity of
the substance it is testing.
You will be investigating the pH range 1 - 11. You will need to match
your pH paper with a colour to determine the pH of the substance you are
testing.
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Colour
maroon
red
deep orange
orange
light orange
yellow/mustard
light green
grass green
dark green
deep blue/green
dark blue
Shade
You are about to create a colour scale by which you can gauge colour
changes in the pH paper. Use coloured pencils or textas to colour in the
blank boxes below with the shade indicated below each box. You may need
two different colours to create the correct shade in each box.
pH
1
2
3
4
5
6
7
8
9
10
11
You will be using the colour scale you just made for experiments later in
this part. You may need some practice to read the correct pH from the
scale and determine if it indicates acidity or alkalinity or neutrality.
State the pH of the following shades of pH paper and the acidity or
alkalinity they indicate. You may use the boxed information on page 12 to
help you determine acidity and alkalinity. The first one has been done for
you as a guide.
Shade of pH paper
dark green
pH
Acidic/alkaline
9
weakly alkaline
orange
deep blue/green
deep orange
light green
maroon
yellow/mustard
Check your answers.
Part 4: What’s growing on your skin?
13
The pH of skin
Do you recall seeing lipsticks in shops that are green or blue, but change
colour when you apply them? The lipsticks change colour due to the
acidity of the skin.
Often two people can apply the same lipstick, but it will turn a different
colour on each person due to the different acidity levels of each person’s
skin. This lipstick is not to be confused with normal lipstick which stays
the same colour when applied.
Many factors can affect the pH of your skin.
Listen to the Skin pH section of the Skin audiotape/internet audio files. You
may need to listen to the tape several times to answer the following
questions.
1
What is the normal pH range of human skin?
_____________________________________________________
2
Explain the normal pH range in terms of acidity and alkalinity
eg. strongly acidic to alkaline.
______________________________________________________
3
What main factor causes skin to become acidic?
______________________________________________________
______________________________________________________
4
What parts of the body have different pH values?
______________________________________________________
______________________________________________________
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5
Are the pH values that are commonly associated with the parts of the
body outlined in question 4 higher or lower than the rest of the
body? Does this mean they are more acidic, more neutral or more
alkaline?
_____________________________________________________
6
_____________________________________________________
Are more or fewer microbes associated with the underarms,
forehead, toe webs and the soles of the feet?
_____________________________________________________
_____________________________________________________
7
There are two theories why the underarms, forehead, toe webs and
the soles of the feet have higher pH values. Explain those two
theories below.
a)
_________________________________________________
_________________________________________________
_________________________________________________
b)
_________________________________________________
_________________________________________________
_________________________________________________
8
What is the acid mantle?
_____________________________________________________
_____________________________________________________
9
What is thought to be the function of the acid mantle?
_____________________________________________________
_____________________________________________________
10 Some scientists believe that the acid mantle has little to do with the
microflora of skin. What do they suggest has a greater impact on
microbe populations on the skin surface?
_____________________________________________________
_____________________________________________________
Check your answers.
Part 4: What’s growing on your skin?
15
Turn to Exercise 4.1 at the back of this part to discuss the role of microflora
in different parts of the body.
?
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
Skin and hair products
1
Fill in the missing words in the passage below.
Imagine you are a microbe living on a person’s face. You are
comfortable living with a pH of 6.
Suddenly, the person
_______________ their face with a substance that has a pH of 8.
The skin has changed from weakly _________________ to weakly
____________________. You and your friends cannot survive above a
pH of 7.5. You die, along with your friends. The skin surface is no
longer acidic. The ______________ mantle has been altered. Different
___________________ are more able to colonise the area you were living
on. They may cause _____________________ on the skin surface.
Write the questions for the following answers.
2
______________________________________________________
______________________________________________________
Your clean skin could become colonised by different, microbes if the
pH was changed. These microbes could cause disease.
3
______________________________________________________
______________________________________________________
Products used on the skin should have a similar pH to that of skin to
minimise disruption of the acid mantle. The acid mantle protects the
skin from colonisation by harmful organisms.
4
______________________________________________________
______________________________________________________
Substances that are acidic or alkaline have the ability to destroy
living tissue. Products used on the skin with a pH below 5 or above
9 have the ability to damage the skin. The protective layer of skin
can allow the entry of harmful organisms once damaged. Rashes,
skin irritations, infections and disease can result.
Check your answers.
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Testing skin and hair products
1
Next to the bullet points below, write down all the skin and hair
products you have at home. Include as many as you can such as: soaps;
cleansers; shampoos; deodorant, hair spray; ointments; heat rub;
shaving cream; moisturisers; perfume; sunscreen after shave; and
lipsticks. You may need to ask your family what products they use on
their skin.
Do not include dry substances such as eye shadow and blusher as they
are not moist enough to change the colour of the pH paper.
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Were you surprised at the range of hair and skin products in your house?
Did you have enough room to record them all?
Skin and hair products are used by people on a daily basis. Have you
ever thought about how compatible these substances are with your skin?
Do you think they could have the ability to damage your skin or lower
your defence to infection?
You are about to test the pH of skin and hair products in your home and
evaluate their compatibility with skin pH.
Aim
To measure the pH values of a range of skin and hair products.
Apparatus
•
Approximately 20 cm of universal pH paper from your teacher.
•
The pH colour scale from page 13 or the one supplied with pH paper
•
Ten skin and/or hair products.
•
Ten cotton buds or pop sticks (ice cream sticks).
Part 4: What’s growing on your skin?
17
Method
1
Collect ten or more skin and hair products from around the house.
You listed these earlier. Record the product type and brand for each
of the substances.
2
Being careful not to wet or contaminate the pH paper, roll it out on
top of a sheet of paper or absorbent paper. The paper will protect the
table surface.
You may need to weigh
down each end of the pH
paper to keep it flat. If you
have pieces of pH paper
instead of a length of paper,
place these on a clean A4
sheet of paper.
You will need to keep track
of what substance is being
tested on what part of pH
paper. Write the substance
on the paper next to the pH
paper. Refer to the diagram
opposite.
3
Dip a cotton bud or a pop stick into the first substance to be tested.
Remove any excess and dab the substance onto the place allocated
on the pH paper. Be careful to apply only a small amount of the
substance as the substance may spread, contaminating other sections.
Use a different cotton bud or pop stick for each substance being
tested.
Some substances may need to be wetted first or lathered before
sampling eg. soap. If so, be careful not to contaminate the pH paper
with water drops or wet hands.
4
Repeat step three with the remaining substances.
5
When all substances have been applied, use your pH colour scale
from page 13 to determine the pH of each substance. Record these
in the results table.
Some substances such as foundation may mask the pH colour.
Try turning the pH paper over to observe the colour absorbed
underneath.
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Results
Complete your results in the table below. An example is provided.
Skin or hair product
Brand
pH colour
soap
sunlight
yellow/mustard
pH
6
Discussion
Fill in the missing pH values and product names based on your results.
a)
The substances tested ranged from ________ to ________ in pH.
b) ______________________________ was the most acidic substance
with a pH of ________ and ______________________________
was the most alkaline substance with a pH of ________.
c)
Generally the hair products tested range in pH from ________ to
_______.
d) pH values of the skin products tested range from _______ to
_______.
Turn to Exercise 4.2 at the back of this part to draw your conclusions on the
pH values of a range of skin and hair products.
?
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
Part 4: What’s growing on your skin?
19
Summary
1
Write three things you are unsure of about skin microflora
______________________________________________________
______________________________________________________
______________________________________________________
2
What do you need to do to gain an understanding about those points
outlined in question 1?
______________________________________________________
______________________________________________________
3
Write three questions you would ask your teacher about the pH of
skin if you were in class and did not fully understand the concept.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
4
What do you need to do to gain an understanding about those points
outlined in question 3?
______________________________________________________
______________________________________________________
5
a) What pH ranges do the skin and hair products have that you
tested?
__________________________________________________
b) How compatible are these pH ranges with skin pH?
__________________________________________________
__________________________________________________
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Appendix 1
Microbes commonly detected on human skin
Gram-positive cocci
Gram-positive bacilli
Staphylococcus aureus
Corynebacterium jeikeium
Staphylococcus auricularis
Corynebacterium urealyticum
Staphylococcus capitis
Corynebacterium minutissimum
Staphylococcus cohnii
Propionibacterium acnes
Staphylococcus epidermidis
Propionibacterium avidum
Staphylococcus haemolyticus
Propionibacterium granulosum
Staphylococcus hominis
Brevibacterium epidermidis
Staphylococcus saccharolyticus
Gram-negative bacilli
Staphylococcus saprophyticus
Staphylococcus simulans
Acinetobacter calcoacaticus
Yeasts (Fungi)
Staphylococcus warneri
Staphylococcus xylosus
Malassexia furfur
Moulds
Micrococcus luteus
Micrococcus lylae
Micrococcus nishinomiyaensis
Trichopyton mentagrophytes
Mite
Demodex folliculorum
Micrococcus kristinae
Micrococcus sedentarius
Micrococcus roseus
Micrococcus varians
Part 4: What’s growing on your skin?
21
Appendix 2
Example answer to Exercise 4.2
1
Include your used pH paper as shown above.
3
The skin and hair products tested ranged in pH from 5 to 7. Products
within a pH range of 4 to 8 are compatible with skin as skin has a pH
range of 4 to 8, however most skin has a pH of 5.5 to 6. The
moisturisers, deodorants, soaps and hand creams tested are
compatible with skin. Any substances used on skin with pH values
below 4 and above 8 have the potential to change skin pH, thus
altering the acid mantle. This could allow colonisation of the skin
surface by harmful micro-organisms and result in skin irritation or
infection.
This answer is fictitious and does not indicate actual pH ranges of skin and hair
products.
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Suggested answers
The microflora of skin
1
Microflora means micro-organisms surviving as microscopic
communities.
2
Bacteria: single-celled procaryotic organisms belonging to the protist
kingdom.
Staphylococci: cocci bacteria appearing in grape-like formations.
Cocci: sphere-shaped bacteria.
Microbes: micro-organisms.
Micro-organisms: microscopic, often single-celled, organisms.
Sebum: oil produced by sebaceous glands in the dermis.
Epidermis: outermost layer of the skin which protects the underlying
tissue, forms a barrier from heat loss, water loss and
micro-organisms.
Keratin: tough protein present in the epidermis of vertebrate
organisms.
3
Skin varies from dry areas to moist areas and wet areas, therefore
conditions on the skin surface are not uniform.
4
Micro-organisms prefer moist environments.
5
Sweat from sweat glands contains sodium chloride and lactate.
Sebum, an oily substance from sebaceous glands next to hair
follicles, also provides nutrients that encourage micro-organisms.
6
The skin surface is constantly losing clumps of dead skin. Any
microbes on the skin surface are lost. The pH of skin is slightly
acidic – at 5.5 pH. Most microbes prefer a pH neutral environment
of 7. For these reasons, only specific microbes are able to survive on
the skin surface.
7
The action of microflora on the skin causes the oil on the skin to
become acidic. Microbial action on sebum releases smelly gases,
commonly referred to as body odour.
Part 4: What’s growing on your skin?
23
8,9
Species of microflora
Group
Part of body found
Staphylococcus epidermidis
bacteria
upper body and face
Staphylococcus hominis
bacteria
legs and arms
Micrococcus luteus
bacteria
head, legs and arms
Corynebacterium jeikeium
bacteria
arm pit
Propionibacterium acnes
bacteria
face and shoulders
Propionibacterium avidum
bacteria
arm pit
Propionibacterium granulosum
bacteria
side of nose
Brevibacterium epidermidis
bacteria
in between toes
Acinetobacter calcoaceticus
bacteria
groin and front of elbow
Malassezia furfur
fungus
scalp, ear and back
Trichophyton mentagrophytes
fungus
feet
Demodex folliculorum
mite
face
10 a) Cocci look like small round spheres like ball bearings.
Staphylococci resemble a bunch of grapes. (Other answers are
acceptable.)
b) Bacilli look like small rods. One bacillus resembles a chain
with rods linked together. (Other answers are acceptable.)
c) Moulds have threads joining each mould head containing
spores. Bacteria are much smaller, needing a higher power
microscope for viewing and are individuals or groups of spheres
or rods.
11 Refer to the table above to locate areas particular species of
microbes are found.
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Acidity and alkalinity
1
0
strongly acidic
1
2
3
≠
increasing acidity
Æ
neutral pH
Ø
increasing alkalinity
4
5
6
7
8
9
10
11
12
13
14
2
strongly alkaline
a) 4 is acid
b) 6 is weakly acidic
c) 13 is strong alkaline
d) 10 is alkaline
e) 7 is neutral
f)
9 is weakly alkaline
g) 1 is strongly acidic
The pH scale
Shade of pH paper
pH
Acidic/alkaline
orange
4
acidic
deep blue/green
10
alkaline
deep orange
3
acidic
light green
7
neutral
maroon
1
strongly acidic
yellow/mustard
6
weakly acidic
Part 4: What’s growing on your skin?
25
The pH of skin
1
The normal pH range of human skin is 4 – 8.
2
The normal pH range of human skin is acidic to weakly alkaline.
3
Sweat released from sweat glands is released at a pH of 5, causing
the skin to have an acidic surface.
4
The underarms, forehead, between the toes and the soles of the feet
have different pH values than the skin on the rest of the body.
5
The underarms, forehead, between the toes and the soles of the feet
have slightly higher pH values, meaning they are more neutral than
the rest of the body.
6
More microbes are associated with the underarms, forehead, toe
webs and the soles of the feet than the rest of the body.
7
a) The high microbe populations metabolise sweat, sebum and
keratin. Their wastes cause the higher pH levels.
b) Sites such as the underarm are moist and separate to the rest of
the body. For this reason, the pH is higher and more microbes
are able to survive there as a result.
8
The acid mantle is the protective layer on the surface of the skin.
9
The acid mantle is thought to prevent more microbes from
colonising the skin surface, as most microbes prefer a neutral pH.
10 Some scientists suggest that electrostatic forces between the skin
surface and microbes determines skin microflora populations more
than the acidity of skin.
Skin and hair products
26
1
Imagine you are a microbe living on a person’s face. You are
comfortable living with a pH of 6. Suddenly, the person washes
their face with a substance that has a pH of 8. The skin has changed
from weakly acidic to weakly alkaline. You and your friends cannot
survive above a pH of 7.5. You die, along with your friends. The
skin surface is no longer acidic. The acid mantle has been altered.
Different microbes are more able to colonise the area you were
living on. They may cause disease on the skin surface.
2
What could happen to your skin if the pH was changed due to
cleaning products?
3
Why is it important that products used on the skin be a similar pH to
the skin surface?
4
What result could products used on the skin have if they have a pH
lower than 5 or greater than 9?
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Exercises - Part 4
Exercises 4.1 to 4.2
Name: _________________________________
Exercise 4.1
Choose two of these body parts:
•
face
•
arm
•
underarm
•
scalp
•
back
•
feet (and toes).
For each of the two body parts you chose:
•
state all the species of microflora present on the skin in that part of
the body (if you chose the arm, you must include the species existing
on the inside of the elbow)
•
clearly draw an example of one of those species, indicating the
species name (the species name must be scientifically written)
•
explain the source of nutrients for the micro-organisms on that part
of the skin
•
explain the effects of microorganism activity eg. smell, acid
environment.
a)
•
body part
_________________________________________________
•
species of microflora present
_________________________________________________
_________________________________________________
•
diagram and label of one microorganism present at this site.
Part 4: What’s growing on your skin?
27
•
source of nutrients
__________________________________________________
__________________________________________________
•
effects of micro-organism activity
__________________________________________________
__________________________________________________
__________________________________________________
b) •
body part
______________________________________________________
•
species of microflora present
______________________________________________________
______________________________________________________
•
diagram and label of one microorganism present at this site
•
source of nutrients
______________________________________________________
______________________________________________________
•
effects of micro-organism activity
______________________________________________________
______________________________________________________
______________________________________________________
?
28
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
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Exercise 4.2
a)
Attach your pH paper with this section complete with product
names. Appendix 2 includes a graphic showing what your teacher
expects. Put the pH next to the name of each substance tested or
include a results table with this information.
b) Comment on the accuracy of your pH readings of different
substances used on the skin given that you made your own pH scale.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
c)
Most skin has a slightly acidic pH of 5.5 or 6. You have tested the
pH values for a range of skin and hair products. In the space
provided:
•
outline the range of pH values you observed
•
discuss the compatibility of skin and hair products with regards
to pH
•
outline possible consequences of skin and hair products that are
too acidic or too alkaline.
You may refer to Appendix 2, which provides an example answer to
this exercise.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 4: What’s growing on your skin?
29
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Senior Science
HSC course
Stage 6
Lifestyle chemistry
Part 5: Dissolve it!
0
20
I
er
b
to T S
c
O EN
g
in D M
t
a
r EN
o
p
or AM
c
n
2
Senior Science Stage 6 HSC Course
Lifestyle Chemistry
•
Common substances
•
Mixing it up
•
Your skin
•
What’s growing on your skin?
•
Dissolve it!
•
Good medicine
Medical Technology – Bionics
Information Systems
Option
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Contents
Introduction ............................................................................... 2
Solvents .................................................................................... 3
The universal solvent ...........................................................................4
Alcohol as a solvent .............................................................................8
Solvent properties ..............................................................................11
Cosmetics and external medications....................................... 12
Subdermal implants ...........................................................................14
The digestive system............................................................... 16
Summary................................................................................. 19
Appendix 1 .............................................................................. 21
Appendix 2 .............................................................................. 23
Appendix 3 .............................................................................. 25
Suggested answers................................................................. 27
Exercises – Part 5 ................................................................... 31
Part 5: Dissolve it!
1
Introduction
Have you ever wondered why some substances dissolve in water whilst
others do not? In Part 5 you will be given opportunities to learn the
chemistry behind the solubility of substances; the common substances
that contain solvents; and how different types of tablets and medical
implants regulate the released of medication over time. The nature of the
digestive system is also outlined.
In Part 5 you will be given opportunities to learn to:
•
identify water and alcohol as commonly used solvents
•
explain the relationship between the properties of solvents and their
use in cosmetics and external medication
•
identify cosmetics and external medications where water is the
solvent
•
identify cosmetics and external medications where alcohol is the
solvent
•
identify the parts of the digestive system
•
outline the role of the stomach and the small intestine in breaking
down food
•
discuss the difference in pH of the stomach and the small intestine.
In Part 5 you will be given opportunities to:
•
identify data sources, gather, process, analyse and present
information from secondary sources to identify how subdermal
implants release their medication into the body.
Extract from Senior Science Stage 6 Syllabus © Board of Studies NSW,
October 2002. The most up-to-date version is to be found at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html
2
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Solvents
?
1
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
Do you remember the term solvent from Part 1? Write the definition
for a solvent below.
_____________________________________________________
_____________________________________________________
You may not realise that you rely on solvents every day. You wouldn’t
be able to make a cup of tea or a milkshake or toffee without a solvent.
You wouldn’t be able to wash your paintbrushes or take medicine
without it. Soft drink wouldn’t even exist without a solvent.
2
There are two common solvents. Use the clues below to identify the
two solvents.
a) This solvent can dissolve sugar and salt, is very common and
quenches your thirst. Without this solvent, you wouldn’t be able
to make a cup of tea or swim in a pool.
_________________________________________________
b) This solvent is found in nail polish remover and methylated
spirits. It can cause people to act strangely and is regularly
consumed at parties. It begins in a and ends in l.
_________________________________________________
Check your answers.
Part 5: Dissolve it!
3
The universal solvent
Have you ever wondered why water is capable of dissolving same
substances and not others? The chemical concept is not as hard to
understand as it seems.
Water is the universal solvent. It has the ability to dissolve many
substances.
You should be familiar with the chemical formula for water, H2O.
This means that each water molecules contains two hydrogen atoms and
one oxygen atom.
1
On the diagram of a water
molecule opposite, draw a ‘+’
next to each hydrogen atom and
a ‘–’ next to the oxygen atom.
O
H
H
Check your answer before moving on.
2
a) Draw an oval shape
around the water molecule
opposite.
b) Outside the circle on the
side with the oxygen
molecule, write a ‘–‘
symbol. This side of the
molecule has a slightly
negative charge.
O
H
H
c) On the side with the
hydrogen atoms, write a
‘+’ symbol. This side of
the water molecules has a
slightly positive charge.
Check your answer before moving on.
You have just drawn a water molecule with polar ends. This means that
certain ends of the molecule contains a positive or negative charge.
Water molecules are polar.
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3
Imagine a water molecule is like a magnet. One end is positive and
the other end is negative. If you have five magnets, the positive end
of each magnet will be attracted to the negative end of another. The
water molecules below are attracted to each other like magnets.
Some charges are displayed on the molecules. Write in the
remaining charges. (Remember positive and negative charges are
attracted to each other.)
Check your answer before moving on.
If water molecules did not have polar ends, water molecules would not
stick together and life as we know it could not exist.
The strong forces between water molecules are called cohesive forces.
When another substance is added to water with stronger attractive forces
than the water molecules themselves, the water molecules will be
attracted to the new substance, thus dissolving it. This can be likened to
a group of girls at a disco.
Imagine a group of girls sticking together at a disco as water molecules.
The forces holding them together are cohesive forces of positive and
negative attraction. When a group of guys are added to the disco, the
girls might be more attracted to them than each other. If you still
imagine the girls as polar water molecules, they disperse, each becoming
attracted to a boy.
Sugar like water has OH groups. Parts of the molecule is polar.
Therefore, sugar can dissolve in water.
Non polar substances dissolve in other non-polar substances. polar
substances dissolve in polar substances.
Are you confused? If so, you are about to carry out an activity that
should help.
Part 5: Dissolve it!
5
4
Cut out the girl water molecules and boy sugar molecules from
Appendix 1. The girls have their arms out representing the polar ends of
a water molecule. One arm represents the positively charged end and
the other represents the negatively charged end of a water molecule.
The boys also have their arms out, representing the polar parts of sugar
molecules.
The positive ends of water molecules (girls) are attracted to the negative
part of sugar molecules (boys) and vice versa.
Two girls (molecules of water) are attracted to each end of a boy (sugar
molecule). This causes each boy to be surrounded by a ‘jacket’ of four
girls.
Remembering positive and negative charges attract, arrange the water
and sugar molecules from Appendix 1 so that four water molecules
(girls) are holding onto each sugar molecule (boy).
Check your answer before moving on.
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By now, you should understand that:
•
each water molecule contains two hydrogen atoms and one oxygen
atom
•
water molecules are polar with one end positively charged and the
other end negatively charged.
•
water molecules are attracted to each other with cohesive forces
•
polar substances will dissolve in water
•
the polar ends of a substance are attracted to the polar ends of water
molecules, causing the substance to dissolve in the water.
•
a substance that is not polar will not dissolve in water.
If you do not understand the points outlined above, contact your teacher for
help before moving on.
Cordial, sugar in water, salt in water; tea and most disinfectants are
examples of substances with water as a solvent. It is also used to
dissolve acids and alkalis. Your swimming pool uses water as a solvent,
salt and/or chlorine is dissolved in the water.
Even though water is referred to as the universal solvent, it is not as easy
to think of examples where water is used as a solvent only. You could
probably think of many examples where water is used as a base for
colloidal mixtures and suspensions. Water is used in soft drink as a
solvent.
5
Identify four substances where water is used as a solvent.
_____________________________________________________
_____________________________________________________
Check your answers.
?
Part 5: Dissolve it!
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
7
Alcohol as a solvent
There are many different forms of alcohol. You may have heard of
glycerol, ethanol, methanol and phenol. These are just a few forms of
alcohol. The alcohol you are probably the most familiar with is in beer,
wine and spirits. These all contain ethanol. Methylated spirits is mainly
ethanol but is rendered undrinkable by the addition of methanol which is
poisonous in small quantities.
You have learnt about the polar nature of water and why it dissolves
polar substances. The alcohols you will be investigating are mainly
ethanol and methanol. These alcohols differ greatly from water as they
are only slightly polar at one end and non-polar at the other end. This
means that one end of the molecule possesses a charge and the other end
of the molecule has no charge.
List as many substances containing alcohol that you know of. For example,
your list may contain alcoholic drinks or substances used on the skin.
_________________________________________________________
_________________________________________________________
_________________________________________________________
Ethanol and methanol
Ethanol is a widely used solvent. Look at the structure of an ethanol
molecule below. ‘C’ represents carbon atom, ‘H’ represents a hydrogen
atom and OH represents oxygen and hydrogen combined as a hydroxide
group.
H H
H C C OH
H H
The chemical structure of ethanol.
The hydroxide (OH) end of an alcohol molecule is slightly polar, having
a slight charge. The other end is not polar, having no charge.
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1
Draw a molecule of ethanol below. On the hydroxide (OH) end of the
molecule write slightly polar. On the other end of the molecule, write
non-polar.
2
With one polar end and one non-polar end the alcohols, methanol
and ethanol have interesting capabilities. Break the code below to
determine these capabilities.
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
the polar end can dissolve in water and the non-polar end
can dissolve in oil
Write your complete answer in the box below.
Check your answers before moving on.
Larger alcohol molecules
Most of a larger alcohol molecule consists of a hydrocarbon chain made
up of carbon and hydrogen atoms only. This means that larger molecules
of alcohol such as cetyl alcohol are mostly non-polar. They can dissolve
non-polar molecules.
Because most of a larger alcohol molecule dissolves in oil and the rest
dissolves in water, alcohol can be used as an emulsifier between oil and
Part 5: Dissolve it!
9
water. This has many applications especially in the cosmetics industry.
These are discussed later in this part.
By now, you should understand that:
•
ethanol and methanol have a slightly polar end and a non-polar end
•
the polar ends of ethanol and methanol alcohols are able to dissolve
in water
•
the non-polar ends of ethanol and methanol alcohols are able to
dissolve in oil
•
in larger alcohol molecules the polar OH group is only a small part
of the larger alcohol molecule
•
polar substances can dissolve in small alcohol molecules like
methanol and ethanol but not larger alcohol molecules like cetyl
alcohol
•
substances that are weakly polar or non-polar will dissolve in
alcohols because most of any alcohol molecule is non-polar
•
substances dissolving in alcohol are dispersed through the alcohol.
If you do not understand the points outlined above, contact your teacher for
help before moving on.
Alcohols are used as solvents in textas, methylated spirits, stain
removers, imitation vanilla essence, antifreeze, enamel paints, varnishes,
mouth wash, cough mixtures, perfumes, after shave and nail polish
remover.
Identify four substances where alcohol is used as a solvent.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answer.
Turn to Exercise 5.1 at the back of this part to identify different solvents.
10
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Solvent properties
An interesting quality of the alcohols commonly used as solvents,
methanol, ethanol and propanol, is that they evaporate quickly. If an
alcohol is used on the skin surface, it feels cool and soothing. This is
because it removes body heat as it evaporates, leaving the skin with a
‘cool’ sensation. In high enough quantities, alcohol also has the ability to
dehydrate the cells of microbes, causing them to die. Antiseptics and
disinfectants rely on this property of alcohol to kill bacteria.
You have also already learnt that some alcohols can be used as
surfactants and emulsifiers as some have a polar and a non-polar end.
1
Use the points below to record three properties of alcohol from the
passage above.
•
__________________________________________________
__________________________________________________
•
__________________________________________________
__________________________________________________
•
__________________________________________________
__________________________________________________
Water has the ability to dissolve polar substances. You may only be
aware of table salt, however, there are many other salts that dissolve in
water. Acids, alkalis and the alcohols, methanol and ethanol, dissolve in
water. Water evaporates, however not as fast as alcohol, therefore the
cooling effect is not as noticeable. Water also is capable of hydrating
cells.
2
Record three properties of water from the passage above.
•
_________________________________________________
_________________________________________________
•
_________________________________________________
_________________________________________________
•
_________________________________________________
_________________________________________________
Check your answers.
The properties of solvents often determine their use. Some substances
you commonly use contain these solvents.
Part 5: Dissolve it!
11
Cosmetics and external medications
Almost all cosmetics and external medications such as creams, sprays
and ointments contain one or more solvents.
1
Record any cosmetic products or medications you have used on your
skin over the last two weeks. This includes: deodorants, moisturisers,
shaving cream, perfume, soap, after shave, ointment, rash or bite
treatments, burn treatments, heat rubs, disinfectants, nail polish, nail
polish remover and any others you can think of.
If you do not use many of these substances, you may question another
person.
_____________________________________________________
_____________________________________________________
_____________________________________________________
You may have found that you use more substances than you thought.
In most cases, the substance would not exist without a solvent.
Water may also be referred to as aqua in an ingredients list. Alcohol can
have many names. The term ‘alcohol’ or ‘alcohol based’ in a list of
cosmetic ingredients usually refers to ethanol. The following list of
names describe other forms of alcohol used:
•
cetyl alcohol
•
stearyl alcohol
•
cetearyl alcohol (also called cetostearyl alcohol)
•
denatured alcohol
•
lanolin alcohol
•
SD alcohol-A; SD alcohol 40
•
methanol/methyl alcohol.
This list of alcohols does not totally cover the alcohols you are likely to
find in cosmetics and medications, however it is a guide.
12
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Some substances contain water and alcohol. You already know the
properties of water and alcohol. The water is often used as a skin
hydrator as well as a solvent for acids, alkalis, salts and other polar
substances.
In most cases, alcohol is present to dissolve non-polar substances such as
oils. Once the alcohol has dissolved these substances, the alcohol may be
dissolved in the water.
You may find it strange that oils should be present in cosmetics such as
moisturisers, however they play an important role. Oils not only replace
natural oils stripped by washing with soap and cleansers, they coat the
skin surface, minimising the evaporation of water from the skin.
In other instances, alcohol may be present in such things as cleansers,
and toners. Their function here uses the non-polar property to dissolve
away non-polar skin oils. However, skin cosmetics should not contain
greater then the recommended 50% - 60% alcohol as it draws moisture
out of the skin, having a drying effect. Water is also often present in the
substances to help lathering and removal of oils and grime.
The non-polar nature of alcohol also dissolves non-polar molecules with
odours used in perfumes and after shaves. Once applied to the skin, the
alcohol evaporates, leaving a fragrant oil emitting an odour. This is left
on the skin, dissolved in non-ionic skin oils. These odours are quickly
destroyed through abrasion or excess heat.
Disinfectants and some cosmetics rely on relatively high concentrations
of alcohol to draw moisture out of skin micro-organisms, killing them
and reducing the risk of infection.
Are you ready to investigate the cosmetics and skin medications in your
home? If you don’t have many cosmetic products and external
medications in your home, can you visit a supermarket, friend or
neighbour?
Turn to Exercise 5.2 at the back of this part to investigate solvents used in
cosmetics and external medications
?
Part 5: Dissolve it!
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
13
Subdermal implants
Some medications can be placed under the skin surface. The medication
is released over a period of time.
Turn to Appendix 2 on Controlled release drug delivery. Read the entire
appendix then carry out the following activity.
The following diagrams demonstrate what is described in Appendix 2.
Use the information in Appendix 2 to explain what is occurring in each
diagram below.
Stage
1
1
Diagram of subdermal implant
Explanation
inner core with
hydrophobic film
outer core with
hydrophilic film
2
3
4
14
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2
What substance dissolves the outer film, causing medication in the
outer core to be released?
_____________________________________________________
3
Water alone will nor cause the inner film to degrade. What must be
in contact with the inner membrane to cause it to weaken, enabling it
to burst?
_____________________________________________________
4
Explain the function of subdermal implants currently used in
humans.
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answers.
The solubility of medication taken orally determines the absorption of
drugs. The nature of the digestive system determines the solubility and
absorption of drugs.
Turn to Exercise 5.3 at the back of this part to explain how body pH
influences the solubility of medication in subdermal implants.
?
Part 5: Dissolve it!
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
15
The digestive system
Are you able to identify parts of the digestive system? Can you recall the
roles of the stomach and small intestine in the digestion of food? This
section gives you opportunities to refresh your memory or learn about the
digestive system through fun activities.
Listen to the Digestive system section of the Skin audiotape/internet audio
files to guide you through the following activities.
1
Label the parts of the human digestive system using the labels in
Appendix 3.
The human digestive system.
Check your answers before moving on.
16
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2
State the three food types.
_____________________________________________________
3
Use the Digestive system information in the Skin audiotape/internet
audio files to complete the table below.
Organ
Role in digestion
stomach
duodenum
gall bladder
pancreas
small intestine
Part 5: Dissolve it!
17
4
Explain why the stomach and the small intestine have different pH
values.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
5
In general terms, explain the role of the stomach in breaking down
food.
______________________________________________________
______________________________________________________
______________________________________________________
6
In general terms, explain the role of the small intestine in breaking
down food.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
The substances you consume must become soluble through digestion to
be absorbed by the body and used for energy. How soluble a substance
is determines the rate at which it is absorbed by the body.
Turn to Exercise 5.4 at the back of this part to label and state the functions
of parts of the human digestive system.
?
18
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
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Summary
Below is a list of the contents for Part 5. Write three things you learnt
underneath each heading title. Keep your answers brief as they are they
are to represent key concepts only.
The universal solvent
_________________________________________________________
_________________________________________________________
_________________________________________________________
Alcohol as a solvent
_________________________________________________________
_________________________________________________________
_________________________________________________________
Solvent properties
_________________________________________________________
_________________________________________________________
_________________________________________________________
Cosmetics and external medications
_________________________________________________________
_________________________________________________________
_________________________________________________________
Part 5: Dissolve it!
19
Subdermal implants
_________________________________________________________
_________________________________________________________
_________________________________________________________
The digestive system
_________________________________________________________
_________________________________________________________
_________________________________________________________
?
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
Record five things you need to do in the next week for your open-ended
investigation.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
20
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Appendix 1
water
water
sugar
water
water
sugar
water
water
sugar
water
water
sugar
Part 5: Dissolve it!
21
22
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Appendix 2
Controlled release drug delivery
Subdermal implants in animals
An implant placed under the skin surface contains a compressed core and
two layers of film coating. The outer film is compatible with skin tissue
and degrades at a set rate when in contact with water from the body. The
dissolution of the outer membrane releases medication between the first
and second layers of film.
The inner core, protected by the hydrophobic film begins to swell as the
outer film degrades. The inner film is hydrophobic but dissolves at body
pH. Non-polar molecules inside the film become polar when in contact
with body pH. The polar molecules are then more able to dissolve in
body water. The swelling of the inner core, combined with the
dissolving of the inner film causes the inner film to rupture twenty one to
sixty days after implantation. In this way, the core medication is released
in a pulse. The medication is then able to travel through the bloodstream
to target cells.
The overall effect is similar to two injections of a drug with only one
veterinarian bill.
The above information has been adapted from:
Theil, W J. Panagiotidis, J. Controlled Release Drug Delivery,
<http://www.vcp.monash.edu.au/pharmaceutics/res-control.html>
(accessed 17 June 2000)
Subdermal implants in humans
Subdermal implants are currently being used to deliver steady doses of
hormones in females, replacing the contraceptive pill. Such implants are
effective for up to five years.
Part 5: Dissolve it!
23
The slow release of drugs work on similar principles to those outlined
above, however the chemistry behind the slow release of drugs is more
complicated.
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Appendix 3
Cut out the following labels for the human digestive system.
small intestine
stomach
liver
oesophagus
large intestine
duodenum
gall bladder
rectum
pancreas
mouth
Part 5: Dissolve it!
25
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Suggested answers
Solvents
1
Solvents are substances that will dissolve a solute.
2
a) water
b) alcohol
The universal solvent
1
O
H
H
2
O
H
H
3
4
sugar
sugar
sugar
sugar
Part 5: Dissolve it!
27
5
Water is a solvent in cordial, tea with sugar, disinfectants and
swimming pools. (Other answers are acceptable.)
Alcohol as a solvent
1
H H
non-polar
H C C OH slightly polar
H H
2
The polar end can dissolve in water and the non-polar end can
dissolve in oil.
Larger alcohol molecules
Alcohol is used as a solvent in methylated spirits, enamel paints,
after shave and perfumes. (Other answers are acceptable.)
Solvent properties
1
2
•
Alcohol evaporates quickly, having a cooling effect.
•
Alcohol is able to dehydrate living cells, killing them.
•
Some alcohols may be used as surfactants or emulsifiers due to
the polar and non-polar ends of the molecules.
•
Water is able to dissolve polar substances due to the polar nature
of water molecules. This includes acids, alkalis and some
alcohols.
•
Water is able to hydrate cells
•
Water evaporates causing a mild cooling effect.
Subdermal implants
1
28
Stage
Explanation
1
The subdermal implant contains an inner core and outer core.
The inner core is protected by a hydrophobic film and the outer core
is surrounded by a hydrophilic film
2
The outer film dissolves in body water, releasing medication to the
body. The inner core remains protected by the hydrophobic film.
3
As the outer core degrades, water moves into the inner core,
causing it to swell.
4
The inner core eventually ruptures, releasing a pulse of medication
to the body 21 to 60 days after initial implantation.
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2
Water dissolves the outer film, causing medication in the outer core
to be released into the body.
3
The inner core must be in contact with body pH for it to degrade,
allowing it to weaken and burst.
4
Subdermal implants are currently used in humans replacing the
contraceptive pill. The implants can protect females against
pregnancy for up to five years.
The digestive system
1
mouth
oesophagus
liver
stomach
gall bladder
duodenum
pancreas
small intestine
large intestine
rectum
2
3
Part 5: Dissolve it!
The three food types are carbohydrates, protein and fats.
Organ
Role in digestion
stomach
begins digestion of protein and churns food into a
paste; protease enzymes digest protein; the protein is
broken down into peptides; hydrochloric acid helps the
enzymes present to function and kills microbes.
duodenum
receives contents of stomach, bile from the gall
bladder and enzymes from the pancreas; the
digestion of fat which has been broken up into smaller
globules commences; acidic stomach contents are
neutralized so that ph rises to between 6 and 8
gall bladder
secretes bile into the duodenum; bile breaks oil
globules into smaller globules; bile also neutralises
stomach acids, causing the food to become more
alkaline
29
pancreas
enzymes further break down protein, carbohydrate
and starch which are more able to function in the
higher pH conditions
small intestine
the small intestine produces a fluid containing
enzymes to complete digestion of carbohydrates,
protein and fats; peptidase enzymes break down
proteins; lipase enzymes further digest fat; lactase
breaks down milk sugar (lactose) and other enzymes
break down other carbohydrates
carbohydrates have become glucose; proteins have
become amino acids and fats have become fatty acids
and glycerol; these are absorbed across the small
intestine wall into the bloodstream
30
4
The stomach and the small intestine have different pH values as
different enzymes function best in differing levels of acidity and
alkalinity eg. pepsin functions best in the stomach at a pH of 1 to 2
while other enzymes such as protease and lipase function best in a
pH range of 6 to 8.
5
The stomach churns food into a paste and begins to break down
proteins into peptides with protease enzymes.
6
The small intestine contains a mixture of enzymes from the gall
bladder, pancreas and small intestine. Bile breaks down fats into
small globules. Pancreatic juices and juices secreted from small
intestine walls digest proteins, carbohydrates and fats with enzymes.
Once soluble, the digested food may be absorbed into the
bloodstream.
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Exercises - Part 5
Exercises 5.1 to 5.4
Name: _________________________________
Exercise 5.1
The diagram below shows a shaded polar substance (solute) dissolved in
another polar substance (solvent).
1
Is the unshaded solvent in the above diagram water or alcohol?
Explain your answer.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 5: Dissolve it!
31
2
The diagram below shows water, oil and alcohol molecules.
a) Identify the water, oil and alcohol molecules in the legend
below.
b) Outline your reasons for molecule identification in the legend.
Legend
molecule
water/alcohol/oil
reason
c) Explain what is happening in the above diagram using the
words: polar, non-polar, solvent; emulsion; alcohol; water; and
oil. You may use more than one sentence.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
32
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Exercise 5.2
Collect six cosmetics and/or external medications from the following list:
•
deodorants
•
ointment
•
moisturisers
•
rash or bite treatments
•
shaving cream
•
burn treatments
•
perfume
•
heat rubs
•
after shave
•
disinfectants
•
nail polish
•
vapour rubs
•
nail polish remover
•
disinfectants.
Only choose products with ingredients listed on them. Some substances
may list the active ingredient only and are not recommended for your
investigation unless the active ingredient is a form of alcohol. Choose at
least one product that contains no alcohol.
Look at the list of ingredients on the package. Place a tick in the relevant
box to indicate the solvents present. If alcohol is present, place a tick in
the alcohol column. Remember, there are many names for alcohol listed
on page 12. Other alcohols may be present other then those indicated
earlier. If water (aqua) is present, place a tick in the water column.
Water
present
Alcohol
present
Cosmetic
External
medication
Substance
The first one has been done for you as a guide.
Lux® awaken moisturiser
Part 5: Dissolve it!
33
1
a) List the cosmetics and medications containing water only.
__________________________________________________
b) Place a small amount of one of those substances on your skin.
Describe how it feels eg. cold, warm, oily, slimy.
__________________________________________________
__________________________________________________
__________________________________________________
2
a) List the cosmetics and medications containing alcohol only.
__________________________________________________
b) Place a small amount of one of those substances on your skin.
Describe how it feels.
__________________________________________________
__________________________________________________
__________________________________________________
c) Use the information on the properties of alcohol on page 11 to
explain why the substance containing alcohol feels like it does.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
3
a) List the cosmetics and medications containing alcohol and
water.
__________________________________________________
b) Use the information on page 10 to explain why these substances
contain alcohol and water.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
34
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Exercise 5.3
Explain how subdermal implants rely on body pH to deliver medication
to body tissue. You may use diagrams in the space provided below to
help with your explanation.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
?
Part 5: Dissolve it!
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
35
Exercise 5.4
36
1
Label the parts of the digestive system identified with a line on the
diagram below.
2
Fill out the functions in digestion of those parts indicated with a box.
Include as much detail as possible. Show variations in pH.
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Senior Science
HSC course
Stage 6
Lifestyle chemistry
Part 6: Good medicine
0
20
I
er
b
to T S
c
O EN
g
in D M
t
a
r EN
o
p
or AM
c
n
2
Senior Science Stage 6 HSC Course
Lifestyle Chemistry
•
The substances you use
•
Mixing it up
•
Your skin
•
What’s growing on your skin?
•
Dissolve it!
•
Good medicine
Medical Technology – Bionics
Information Systems
Option
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Contents
Introduction ............................................................................... 2
Drug solubility............................................................................ 3
Addictive narcotics ...............................................................................4
Vitamins ................................................................................................5
Tablets ..................................................................................................6
Investigating the rate at which different drug forms dissolve .............8
Drug administration ............................................................................11
Drug action on the body.....................................................................12
Summary................................................................................. 13
Appendix 1 .............................................................................. 15
Appendix 2 .............................................................................. 17
Appendix 3 .............................................................................. 19
Suggested answers................................................................. 23
Exercises – Part 6 ................................................................... 25
Bibliography ............................................................................ 39
Part 6: Good medicine
1
Introduction
Medications can be administered to the body in many different ways.
The choice of administration can depend on the solubility of the drug.
How a drug acts on the body is also closely related to its solubility.
You will learn the differences between common forms of oral medication
and appreciate why water-soluble vitamins need to be a more regular part
of your diet than fat-soluble vitamins.
In Part 6 you will be given opportunities to learn to:
•
account for the absorption of a drug and its action on/in the body in
terms of its solubility
•
explain why a knowledge of the solubility of materials can be used
to design drugs for specific tasks
•
identify that the manner of administration of a drug may be related to
its solubility
•
identify vitamins that are water-soluble and those that are fatsoluble.
In Part 6 you will be given opportunities to:
•
perform an investigation to gather data comparing the rate at which
capsules, tablets, enteric coated tablets and slow-release tablets
dissolve
•
gather, process and analyse information from first-hand or secondary
sources to relate the significance of solubility of a medication to its
action on/in the body.
Extract from Senior Science Stage 6 Syllabus © Board of Studies NSW,
October 2002. The most up-to-date version is to be found at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html
2
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Drug solubility
Have you ever taken medication that made you feel drowsy? Have you
heard of medication that won’t make you drowsy? Drug companies
design their drugs to cause specific reactions such as relief from colds
and flus. How the drug acts on the body and the effects it causes is often
determined by the solubility of the drug.
You know that non-polar substances will dissolve in fats and polar
substances will dissolve in water.
Nerves in the brain are insulated with myelin which is made up of 80%
fat. Body cells are also surrounded by membranes containing fats.
Nerves throughout the body send messages across gaps between their
connecting nerve fibres. The signal between nerve fibres is transferred
by the movement of small polar molecules with positively charged
nitrogen atoms. The blood and lymph that circulates throughout the
body is mostly water and so readily carry water soluble polar substances.
Although the movement of messages across the gap from one nerve fibre
to the next involves polar molecules, some non-polar drugs can affect
transmission of nerve messages. Certain non-polar drugs coat the ends of
nerve fibres and slow or stop messages from getting through.
1
Circle the correct word in the following sentences based on the above
information.
a) A polar/non-polar drug will be absorbed more readily into brain
cells through fatty membranes.
b) A polar/non-polar drug could affect connections between nerves in
the body
Check your answers before moving on.
2
Reconstruct the following sentences.
a)
diffuse Non-polar drugs brain membranes cell will across easily.
b) drowsiness The cause may drugs.
_________________________________________________
Part 6: Good medicine
3
It is clear that a knowledge of drug solubility is essential for designing
drugs for specific tasks in the body. This is demonstrated by comparing
addictive narcotic drugs.
Addictive narcotics
Narcotics are drugs that produce general anesthesia (narcosis) of the
body. Whether drowsiness or unconsciousness or death occur depends
on the quantity, quality and extent of any previous intake of the drug.
Opium is a juice obtained from unripe
seeds of the oriental poppy plant. About
10% of the mass of opium is morphine.
Morphine injections are used to relieve
extreme pain in injuries and terminal
cancer patients. The morphine is carried
throughout the body in the blood and can
pass across the blood-brain barrier and
affect the brain. Morphine can relieve
pain from nerves at the site of an injury
as well as dull the pain receptors in the
brain.
Heroin is diacetyl morphine. Heroin is a
less polar molecule called an ester made
by reacting morphine, an alcohol, with
acetic acid. Because heroin is less polar
than morphine it passes through the fat
layers of the brain more quickly. Heroin
has similar effects on the human body to
morphine but produces a stronger
addiction, more difficult to cure.
Whereas morphine is a natural product
and heroin a slightly modified natural
product made by reacting morphine with
acetic acid, methadone is synthesised
from simpler chemicals. The synthetic
narcotic methadone is used to cure
heroin addiction. It is addictive like
heroin but does not produce a stupor like
heroin.
CH3
N
HO
OH
O
Morphine – the OH groups and
N atom make it polar enough to
dissolve in blood
CH3
N
O
O
CH3C O
O
O CCH3
Heroin (diacetyl morphine) –
less polar than morphine so
passes through fat layers of the
brain more quickly
CH3
N
CH
C
CH3
CH3
CH2CH3
O
Methadone – a synthetic
product made from chemicals
derived from petroleum
A person undergoing methadone treatment for heroin addiction is better
able to cope with work but it still an addict, possibly for life.
4
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The Centre for Green Chemistry at Monash University in Victoria is
doing research on producing non-addictive forms of morphine. Research
workers are adding highly polar groups containing N atoms to morphine.
These highly polar forms of morphine will stay in the blood and relieve
pain at the site of injury. The highly polar molecules are not able to
penetrate the fatty barriers between the blood and brain. It is hoped that
the patient will remain conscious as their brain is unaffected and they
will be relieved of pain coming from the site of injury.
Vitamins
How vitamins are absorbed and stored in the body is also dependant on
solubility.
Vitamins B and C are water-soluble and can easily ‘stick’ to water
molecules in the blood and be circulated to where they are needed in the
body. The polar nature of these vitamins however, also causes them to
be easily removed from the body in urine. These vitamins therefore need
to be consumed regularly, preferably each day.
Vitamins A, D, E and K are fat-soluble and can easily be absorbed into
cells through cell membranes. This can cause them to accumulate inside
cells. If too many of these vitamins accumulate in the body as a result of
taking too many vitamin supplements they can have a toxic effect. These
fat-soluble vitamins do not have to be consumed every day in a balanced
diet but should be part of the diet each week.
Many homes have at least one bottle of vitamins. Look for a bottle of
vitamins at home. If you don’t have any, again, ask a friend or neighbour.
Aim to find a multivitamin container, however any vitamins are fine such as
vitamin B complex.
1
Place a tick in the column below if your vitamin container indicates
any of the following vitamins.
Vitamin
Present in vitamin sample
A
B
C
D
E
K
Part 6: Good medicine
5
2
Write the instructions for adult use eg. ‘Take three times daily with
food.’
______________________________________________________
______________________________________________________
With your knowledge of water-soluble and fat-soluble vitamins, explain
why the dose must be taken as instructed. Outline the risks if not taken as
instructed.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Check your answers.
?
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
Tablets
Tablets can come in many shapes, sizes and colours, with and without
coatings. Capsules are another form of oral medication.
Use the space below to draw the shapes of four different tablets you have
seen eg. Disprin®, Asprin®, cold and flu tablets and vitamins.
1
6
Appendix 1 contains information about the solubility of tablets,
capsules, enteric coated tablets and slow-release tablets. Use the
information in Appendix 1 to fill in the following table.
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Tablet
Activity in the stomach
Activity in the small intestine
tablet
enteric
coated tablet
capsule
slow-release
tablet
Check your answers.
2
Write two exam type questions and their answers on the solubility of
different types of tablets from the information in Appendix 1.
a)
_________________________________________________
_________________________________________________
_________________________________________________
b)
_________________________________________________
_________________________________________________
_________________________________________________
Turn to Exercise 6.1 at the back of this part to demonstrate your
understanding of the solubility of different tablets.
?
Part 6: Good medicine
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
7
Investigating the rate at which
different drug forms dissolve
Aim
To compare the rate at which a variety of drug forms – capsules, tablets,
enteric coated tablets, and slow-release tablets – dissolve.
Apparatus
You will need to obtain a variety of drug forms such as:
•
capsules (these usually have a cylindrical shape with rounded ends,
the capsule is made of a hard jelly like material; do not get capsulets
which are tablets in the shape of a capsule)
•
tablets (typically hard, disc shaped)
•
enteric coated tablets (coated with a plastic looking material)
•
slow-release tablets (sometimes marked 12 hour or some other time
release)
Ideally they should be different forms of the same drug, containing about
the same amount of drug in each. However it is extremely unlikely you
will be able to find the same drug in the four drug forms listed. Aspirin
and paracetamol are two pain relief drugs that come in a variety of forms
but you may find it difficult to find more than three forms at a local
supermarket or pharmacy. You may be better off looking to see what
old, unwanted medications you have at home in the form of capsule,
tablet, enteric coated tablet and slow-release tablet.
Some changes should be observed in the first few minutes, other changes
within an hour. The last observations could be made after 24 hours.
8
•
You will also need a number of identical transparent containers to
hold liquid and the drug forms.
•
The liquid used to test solubility could be just water. Acid
conditions (as in the stomach) could be investigated by using vinegar
(about 5% acetic acid). Alkaline conditions (as in the small
intestine) could be investigated by using about 5% solutions of either
sodium bicarbonate (bicarb of soda) or sodium carbonate (washing
soda).
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Temperature of the solutions could be room temperature or could be kept
closer to human body temperature by placing containers in a warm place
(away from the reach of animals and children).
Method
When you have at least three of the four drug forms, set up your
equipment with suitable labelling, away from the reach of animals and
children.
•
Aim for valid (effective) results and reliable (trustworthy) data.
•
Modify procedures as needed and analyse the effect of these
modifications.
•
Repeat trials of experiments where appropriate.
•
If you investigate variables such as the acidity/alkalinity of the
solution make sure that you use a control such as water.
•
Where possible record quantitative, rather than qualitative, data.
If you cannot observe any change in the drug forms after a reasonable
time try stirring each container in the same way for the same amount of
time. This simulates what happens in the human stomach and small
intestine where muscular walls move to mix the contents.
If you are carrying out the activity in low room temperatures and not
observing much change transfer the apparatus to a warmer place. Most
chemical processes proceed faster at higher temperatures.
Results
Record these in a table.
Part 6: Good medicine
9
Conclusions
If you wish to see a HSC question based upon having done this
activity and to see the responses given by HSC candidates then use
the NSW HSC 2001 standards package CD-ROM 15340 for Senior
Science.
Refer to question 17 (6 marks) about assessing the validity of
conclusions drawn from this investigation. The three Band 5/6
responses provided for this question will show you what is required
for full, or close to full, marks.
If you do not have access to this standards package contact your
teacher for help.
10
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Drug administration
Have you ever had a needle? Did it hurt? Would you rather have taken a
tablet? Some drugs cannot be administered orally because they will be
destroyed be acids and enzymes in the digestive system or the drug
molecules are too large to be absorbed through the lining in the small
intestine. Tablets and injections are only two forms of medication.
Can you think of any other forms of medication? (You studied two of them
in the last part.)
_________________________________________________________
_________________________________________________________
Appendix 2 explains the use of different forms of medication. Read this
information, then carry out the following activity.
Use the information in Appendix 2 on Drug administration to answer the
following true/false questions. Write a ‘T’ or ‘F’ in the space next to each
statement.
1
Drugs can be administered orally.
2
The manner of drug administration can depend on the speed of
relief required.
3
Asthma medication in most commonly injected.
4
Medication cannot be administered through the skin.
5
Medication required to circulate around the body needs to be
polar.
6
Anaesthetic must be polar to remain inside localised cells.
7
The same drug may be administered in more than one way.
8
The nature of target cells is not important in the designing of
drugs.
9
Drugs in nasal sprays often circulate around the body once
administered.
10 Insulin is non-polar.
Check your answers.
Drugs that are injected often need to act on the body quickly and are
needed in a particular part of the body. Sometimes these medications
cannot be absorbed through the skin, stomach, nasal passages or lungs.
Part 6: Good medicine
11
Oral medications can be self administered and absorbed through the
digestive system.
Medications that use inhalers often work on the tissue immediately,
remaining in lung cells. Nasal sprays focus drugs in the cells in nasal
passages, also acting quickly.
Dermal patches are easy to use. They can concentrate their medication in
a particular area or administer soluble drugs to flow around the body.
You should understand from the information you just gathered that if
medication is to be absorbed into cells in the body through membranes
made of fats, the drugs must be fat-soluble. Do polar or non-polar
substances dissolve in fats? If you are unable to answer that question,
you should look up the answer in Part 4 now.
If medication is to be circulated around the body with the blood, it must
be water-soluble. Do polar or non-polar substances dissolve in water?
Again, if you cannot answer this question, find the answer in Part 4.
It is essential you understand the difference between fat-soluble and
water-soluble substances and their relationship between non-polar and
polar substances for you to understand the next section. If you are not
sure, revise Part 4 or contact your teacher for help.
Drug action on the body
Appendix 3 contains information on four different drugs used externally.
There are six essential points you need to know before gathering
information from Appendix 3 and carrying out Exercise 6.2.
•
polar substances will dissolve in water
•
non-polar substances will dissolve in fats
•
cells are surrounded by membranes made up of fats
•
blood flows through the body as a water based mixture
•
alcohol has polar and non-polar ends
•
water is polar
Miscible means ‘mixing’. Miscible substances such as ethanol C2H5OH
and water HOH mix freely with one another. A drug which is difficult to
dissolve in water can be dissolved in ethanol first and then water added.
This produces an alcohol based solution of the drug in aqueous alcohol.
Turn to Exercise 6.2 at the back of this part to relate the significance of
medication solubility and its action on the body.
12
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Summary
Complete the sample test in Exercise 6.3 to gauge your progress in Lifestyle
chemistry.
?
What progress have you made towards your open-ended
investigation from Part 3? Your report must be submitted
with Part 6 or by a date specified by your teacher.
Complete your open-ended investigation report in Exercise 6.4 at the back of
this part unless your teacher has specified a different date for its submission.
Part 6: Good medicine
13
14
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Appendix 1
Tablets, capsules, enteric coated tablets
and slow-release tablets
Tablets are typically broken down in the stomach. Some of the drug is
absorbed in the stomach, however, most is absorbed through the small
intestine. A spherical tablet has less surface area per volume than a disc
shaped tablet. Therefore, the shape of the tablet affects the rate of drug
dissolution and absorption.
Many drugs are destroyed in the low pH of stomach acid. Some drugs
can irritate or damage the tissue in the oesophagus or stomach.
Capsules and enteric coated tablets are designed to overcome such
problems. The coating surrounding each is not affected by strong acid.
This protects the drugs until they pass into the small intestine. Here, the
pH is at 6 – 8. Capsule and enteric coatings begin to dissolve here,
releasing the drugs within. This prevents the drug from irritating the
stomach and possibly causing bleeding. Capsule and enteric coatings
dissolve at different rates, therefore releasing their drugs at different rates
while in the small intestine.
Slow-release tablets often contain two or more films. The outer film
protects the outer core medication. The inner film protects the inner core
medication. As the outer film gradually dissolves, the outer core
medication is gradually released. Once almost all the outer core
medication is released, the inner film dissolves, gradually releasing
medication. Refer to the diagram below.
outer film
inner film
outer core
(containing
medication)
inner core
(containing
medication)
outer core medication
is released as outer
film dissolves
inner film dissolves,
releasing medication
after the outer core
has dissolved
The action of a slow-release tablet as it travels through the small intestine.
Part 6: Good medicine
15
Different slow-release tablets release their medication in different ways
however, slow-release tablets are generally taken once daily. One slowrelease tablet can release medication for as long as it remains in the
intestine.
Medication is absorbed into the body as a result of diffusion. The
concentration of a drug in the small intestine must be greater than that in
the body for the drug to be absorbed. For this reason, a great deal of
drugs taken orally are lost as waste.
Glossary of some solid dosage medication forms
If you look at a range of medications you will find that the
pharmaceutical industry has been creative in making up new words to
describe its products:
16
cap
abbreviation for capsule
caplet
tablet of capsule shape
capseal
gelatin coated tablet of capsule shape
capsule
cylinder shape with rounded ends, usually made
of gelatin and in two parts that can be opened
dispersable tablet
tablet containing soluble solid acid and a
carbonate that react with water breaking the
tablet apart as it efffervesces
effervescent tablet
same as dispersable tablet defined above
enteric
coating that is stomach acid resistant but
soluble in the alkaline small intestine
gelcap
gelatin coated tablet
meltlet
melt in mouth tablet
minicap
gelatin coated tablet or small capsule
slow-release
designed to provide slow release over time
tab
abbreviation for tablet
tabsule
capsule shaped tablet
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Appendix 2
Drug administration
Some medications are required to circulate around the body such as
antibiotics and insulin. There would be little use in taking antibiotics for
an infected cut in your foot if the antibiotics were not soluble enough to
get from your digestive system to your foot. Other medications are more
useful in specific cells.
Asthma medication often needs to remain in lung cells. Anaesthetic is
required to numb pain sensors in a specific area of the body.
Dermal patches for warts aim to deliver their medication to a localised
wart on the skin. Drugs present in nasal sprays generally remain in nasal
cells to minimise the build up of mucus.
There are two main rules for the designing of drugs.
•
If the drug is to enter cells and remain there, it must be non-polar
(or fat soluble) in order to cross the cell membrane then become
polar once inside the cell. A nitrogen atom in a drug can attract a
positive hydrogen ion and change the drug from slightly polar to
polar.
•
If the drug is to circulate around the body, it must be polar to be
carried by water in the blood.
Take a look at the medications discussed: antibiotics, insulin, asthma
medication, anaesthetic, wart patches and nasal sprays.
The administration techniques used for these drugs differ greatly.
Drugs may be administered orally, through the digestive system; injected
into the bloodstream or muscle; inhaled into the respiratory system;
absorbed through the skin; or absorbed through the nasal passages.
The manner of administration is dependant on four key elements.
•
the speed of relief required
•
the target cells and the ease of access
•
the solubility of the drug
Part 6: Good medicine
17
•
ease of administration.
Insulin is destroyed in the digestive system. For this reason it is injected
into the bloodstream where it can take immediate action. Ventolin® and
other asthma medications are inhaled to access the lung cells directly and
offer fast relief. Nasal sprays work in a similar way, remaining in nasal
cells. Antibiotics may be injected, however they are most commonly
taken orally for self administration purposes. Dermal patches can be
used to act on local skin cells only and can be easily administered.
The manner of drug administration is therefore clearly dependant on:
18
•
the action required on the body
•
the solubility of the drug
•
ease of administration
•
the speed of delivery.
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Appendix 3
The information below has been sourced from:
Orion Laboratories Pty Ltd., Western Australia. Material safety data sheets,
<http://www.orion.net.au/> (accessed 4 July 2000).
Surgical spirit
USES
For drying and astringent action on the skin or as a solvent.
PHYSICAL PROPERTIES
Description:
Clear, colourless, spiritous liquid with an odour of Methyl
Salicylate.
Solubility in Water:
Miscible
INGREDIENTS
Chemical Entity
Proportion
Methyl salicylate
<10%
Diethyl phthalate
<10%
Castor Oil
<10%
Methylated Spirit
to 100%
PRECAUTIONS FOR USE
PERSONAL
PROTECTION
Part 6: Good medicine
Avoid eye contact. If spillage or splashing are likely to occur
during handling, wear safety spectacles. Approved barrier
creams may prove useful in preventing dermatitis when
prolonged skin contact is unavoidable.
19
Benzoin compound tincture B.P.C.
USES
Benzoin Compound Tincture is used mainly as an inhalation
(5 mL to 500 mL of hot water) in bronchitis and acute
laryngitis. It may be applied undiluted as an antiseptic and
styptic to small cuts and to intact skin as a protective
dressing under occlusive plasters and bandages.
PHYSICAL PROPERTIES
Description:
A dark brown alcoholic liquid.
Solubility in Water:
Miscible
Pack Size:
50 mL
INGREDIENTS
Chemical Entity
Proportion
Ethanol (alcohol)
>70%
Benzoin
10%
Prepared Storax
7.5%
Tolu Balsam
2.5%
Aloes
2%
Water
<10%
PRECAUTIONS FOR USE
PERSONAL
PROTECTION
20
Avoid eye contact. If spillage or splashing are likely to occur
during handling, wear safety spectacles. Approved barrier
creams may prove useful in preventing dermatitis when
prolonged skin contact is unavoidable.
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Brilliant green and crystal violet paint B.P.
USES
Marking of skin prior to surgical procedures.
PHYSICAL PROPERTIES
Description
A dark coloured solution with an alcoholic odour.
Solubility in Water
Miscible
pH
Not known
Pack Size
25 mL
INGREDIENTS
Chemical Entity
Proportion
Ethanol
42 - 48%
Brilliant Green
0.5%
Crystal Violet
0.5%
Water
To 100%
PRECAUTIONS FOR USE
PERSONAL
PROTECTION
Part 6: Good medicine
Avoid eye contact. If spillage or splashing are likely to occur
during handling, wear safety spectacles. Gloves and protective
clothing may be worn as the product stains skin and clothing.
21
Gluticol
USES
As a test dose for Glucose Tolerance Testing in cases of
suspected glucose intolerance for Diabetes Mellitus, or as a
calorific supplement.
PHYSICAL PROPERTIES
Description:
An orange liquid with a characteristic orange odour.
Solubility in Water:
Miscible
pH:
1.5 - 3.5
INGREDIENTS
Chemical Entity
Proportion
Glucose Anhydrous B.P.
30 -60%
Citric Acid Anhydrous B.P.
< 10%
Methyl Hydroxybenzoate B.P.
< 10%
Benzoic Acid B.P.
< 10%
Colour
< 10%
Flavour
< 10%
Water Purified
to 100%
PRECAUTIONS FOR USE
PERSONAL
PROTECTION
22
Personal protection is not necessary. Spillage will be sticky and
may stain clothing.
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Suggested answers
Drug solubility
1
a) A non-polar drug will be absorbed more readily into brain cells
through fatty membranes.
b) Either answer could be correct:
A polar drug could affect connections between nerves fibres if it
interfered with the movement of small polar molecules
A non-polar drug could affect connections between nerves in
the body by coating the ends of the nerve fibres.
2
a) Non-polar drugs will diffuse across brain cell membranes easily.
b) The drugs may cause drowsiness.
Vitamins
Vitamins should be often taken with food and liquid to increase their
solubility for absorption. If too many vitamins are taken, it can have a
poisonous effect on the body. Other answers are acceptable.
Tablets
Tablet
Activity in the
stomach
Activity in the small intestine
tablet
the drug dissolves
and some is
absorbed
absorption
enteric
coated
tablet
drug is protected
by enteric coating
enteric coating dissolves; the drug then dissolves
and is absorbed
capsule
drug is protected
by capsule coating
capsule coating dissolves; the drug then
dissolves and is absorbed
slowrelease
tablet
drug is protected
by film coating
outer coating slowly dissolves, releasing outer
layer of medication; inner film then dissolves,
releasing inner core medication for absorption
Part 6: Good medicine
23
Drug administration
24
T
1
Drugs can be administered orally.
T
2
The manner of drug administration can depend on the speed of
relief required.
F
3
Asthma medication in most commonly injected.
F
4
Medication cannot be administered through the skin.
T
5
Medication required to circulate around the body needs to be
polar.
F
6
Anaesthetic must be polar to remain inside localised cells.
T
7
The same drug may be administered in more than one way.
F
8
The nature of target cells is not important in the designing of
drugs.
F
9
Drugs in nasal sprays often circulate around the body once
administered.
F
10 Insulin is non-polar.
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Exercises - Part 6
Exercises 6.1 to 6.4
Name: _________________________________
Exercise 6.1
Imagine you are a senior chemist in a leading drug company.
The research scientists in your firm have discovered a drug that will
target and destroy cancer cells in patients. They need a simple way of
administering the drug. They come to you for advice concerning oral
administration of the drug through tablets, capsules, enteric coated tablets
or slow release tablets.
You look at the structure of the drug. It could easily be destroyed in
stomach acid.
1
What three options for oral medication do you have knowing the
drug would be destroyed in the stomach? Explain your answer.
_____________________________________________________
_____________________________________________________
_____________________________________________________
2
You test the drug. It is non-polar. What does this tell you about the
drug and why is this important?
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 6: Good medicine
25
3
The structure of the drug is similar to other medicines which can
cause irritation in the small intestine. You know that the drug must
be released slowly throughout the small intestine to minimise
irritation. What form of oral administration do you suggest for this
drug and why?
______________________________________________________
______________________________________________________
______________________________________________________
4
Because the drug is non-polar, you know the drug will not be
adequately absorbed without some fats present. What would happen
if the drug was taken on an empty stomach and why?
______________________________________________________
______________________________________________________
______________________________________________________
5
What would you suggest be put on the label under in the ‘directions
for use’ to overcome this problem? Explain your answer.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Exercise 6.2
1
Draw up a table in pencil with six columns and five rows. You may
choose to draw a draft table first before recording your final version
on the following page.
2
Write these headings in each column from left to right: medication;
contains alcohol; contains water; water-soluble; fat-soluble; and will
cross cell membranes. You should now have all the headings filled
in.
3
The titles for each of the four remaining rows are: benzoin
compound tincture B.P.C.; brilliant green and crystal violet paint
B.P.; gluticol; and surgical spirit. Write these names in the far left
column. These names match the medications in Appendix 3.
Your table should now have labels across the top and down the left side.
26
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4
Use the data in Appendix 3 to place ticks or crosses in the relevant
columns eg. Surgical spirit contains alcohol and no water – place a
tick in the contains alcohol column and a cross in the contains water
column. Note that the names of alcohols usually end in –ol.
You will need to draw your own conclusions whether the drug will
cross cell membranes based on ingredient and solubility information.
5
After you have completed the table, create an appropriate title for the
table. Write this above the table then underline it.
Part 6: Good medicine
27
Use the information in the table to answer the questions on the following
page.
6
Which medication(s) will be absorbed by body cells? Explain why.
______________________________________________________
______________________________________________________
7
Which medication(s) will not be easily absorbed by cells in the
body? Explain why.
______________________________________________________
______________________________________________________
8
Some of the drugs outlined in Appendix 3 contain both water and
alcohol. Identify these drugs.
9
If drugs are transported through the blood to target cells in the body,
explain why is it important the drugs have non-polar and polar
characteristics.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Exercise 6.3
Complete the following practice test to gauge your progress in Lifestyle
chemistry.
Multiple choice questions (worth one mark each)
1
A colloid is a mixture that:
(A) leaves no residue when filtered
(B) a beam of light cannot be seen in
(C) contains particles smaller than 10-6 mm in diameter
(D) contains solids which settle out over time.
2
Some insect are able to walk on water because:
(A) water molecules have strong adhesive forces
(B) water molecules contain hydrogen and oxygen atoms
(C) water molecules have strong cohesive forces
(D) insects are not able to walk on water.
28
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3
Oil is immiscible in water unless an emulsifier is added.
The emulsifier holds oil globules in the water by:
(A) separating oil globules
(B) repelling other emulsifiers with the same charge
(C) surrounding oil globules
(D) all of the above.
4
Salad dressing made with half a cup of oil, a quarter of a cup of
lemon juice and a teaspoon of sugar is a colloid. Which of the
following colloid types best describes this colloid?
(A) oil-in-water colloid
(B) solid-in-liquid colloid
(C) water-in-oil colloid
(D) gas-in-liquid colloid
5
A solvent:
(A) is the liquid a solute dissolves in
(B) may be polar or non-polar
(C) may be water or alcohol
(D) all of the above.
6
Which of the following statements is not true?
(A) tablets without coatings mainly dissolve in the small intestine
(B) medication in enteric coated tablets is absorbed in the small intestine
(C) medication in capsules is protected while in stomach acid
(D) slow release tablets release their medication throughout the
intestines.
7
The diagram above could represent:
(A) a surfactant
(B) an emulsifier
(C) an alcohol molecule
(D) all of the above.
Part 6: Good medicine
29
8
Identify the parts of the digestive system labeled with the letters
W, X and Y respectively.
w
x
y
(A) oesophagus, stomach, small intestine
(B) stomach, gall bladder, pancreas
(C) liver, stomach, large intestine
(D) stomach, pancreas, liver
9
Vitamins A, B and C are respectively:
(A) water-soluble; fat-soluble; water-soluble
(B) water-soluble; water-soluble; fat-soluble
(C) fat-soluble; water-soluble; fat-soluble
(D) fat-soluble; water-soluble; water-soluble.
30
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10 The method used for drug administration depends on:
•
the speed of relief required
•
the target cells and the ease of access
•
the solubility of the drug
•
ease of administration.
A doctor gives a patient who is suffering an acute asthma attack an
injection of cortisone. Which of the four factors above is most important
in deciding the method of drug administration in this case?
(A) the speed of relief required
(B) the target cells and the ease of access
(C) the solubility of the drug
(D) ease of administration
Short answer questions (worth three marks each)
11 Briefly explain why water drops are spherical in shape.
_____________________________________________________
_____________________________________________________
_____________________________________________________
_____________________________________________________
12 a) Explain the role of the acid mantle on human skin.
_________________________________________________
b) Explain why skin and hair products must be compatible with
skin pH.
_________________________________________________
_________________________________________________
_________________________________________________
Part 6: Good medicine
31
13 Two common solvent are water and alcohol. List three properties of
each that make them useful in cosmetics.
a) water
__________________________________________________
__________________________________________________
__________________________________________________
b) alcohol
__________________________________________________
__________________________________________________
__________________________________________________
14 a) Give three examples of gas-in-liquid colloids.
__________________________________________________
__________________________________________________
b) You made some mixtures which were either suspensions or
colloids during this topic. Choose one of these and briefly
outline how it was made.
__________________________________________________
__________________________________________________
__________________________________________________
15 Explain why the solubility of a drug is important in designing a drug
for a specific task.
______________________________________________________
______________________________________________________
______________________________________________________
16 a) Shower gels, soaps and shampoos contain some similar
ingredients. Explain the main functions of shower gels, soaps
and shampoos.
__________________________________________________
__________________________________________________
32
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b) Define the term biodegradable and indicate the difference in the
biodegradability of soaps and detergents used today.
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
17
a) What pH value does the stomach have?
b) What pH value does the small intestine have?
c) Explain why the difference in acidity between the stomach and
the small intestine is important in the digestion of food.
_________________________________________________
_________________________________________________
_________________________________________________
18 Explain the role of the following organs in the digestion of food.
liver
_____________________________________________________
_____________________________________________________
gall bladder
_____________________________________________________
_____________________________________________________
pancreas
_____________________________________________________
_____________________________________________________
Part 6: Good medicine
33
19 The diagrams on the right show the stages of medication release
from a subdermal implant. Next to each diagram briefly explain
what is occurring in each stage.
a)
__________________________
__________________________
b)
__________________________
__________________________
c)
__________________________
__________________________
Extended answer questions (worth five marks each)
20 a) Underarm skin has different conditions to skin on the arm.
Explain the different conditions on these parts of the body.
__________________________________________________
__________________________________________________
b) Is the pH of skin in underarms more or less acidic than skin pH
on the arm?
c) The relationship between the pH, nutrients present, moisture
availability and the microflora present on under arm skin is a
controversial one. Discuss the various ideas on the relationship
that is thought to exist between the microflora found in under
arm skin, the skin pH and the conditions that exist there.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
34
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21
a)
Species of microflora
Part of body found
Staphylococcus epidermidis
upper body and face
Staphylococcus hominis
legs and arms
Micrococcus luteus
head, legs and arms
Corynebacterium jeikeium
armpit
Propionibacterium acnes
face and shoulders
Propionibacterium avidum
armpit
Propionibacterium granulosum
side of nose
Brevibacterium epidermidis
in between toes
Acinetobacter calcoaceticus
groin and front of elbow
Malassezia furfur
scalp, ear and back
Trichophyton mentagrophytes
feet
Demodex folliculorum
face
Use the information in the table above on skin microflora to label the
microflora present on the sites indicated on the diagram below.
Part 6: Good medicine
35
b) Explain what could happen to skin microflora and the skin if a
product was used with a pH of 9.
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
22 Draw five diagrams showing oil being acted on by an emulsifier.
Explain what is happening at each stage.
36
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Exercise 6.4
You should have made significant progress on your open-ended
investigation. Your completed report should be sent to your teacher with
this section, unless another date has been specified by your teacher.
Use your own paper to complete your report based on your plan from
Exercise 3.4.
The following information outlines what your teacher expects in your
report.
Aim
What are you trying to find out? What product(s) are you testing?
Apparatus
What and/or who will you need to carry out your investigation?
Method
How will you carry out your investigation? Organise each step
sequentially. How will you collect results? Will your data be
quantitative (measured) or qualitative (compared against each other)?
Indicate your dependent variable (what you are interested in measuring)
and independent variables (quantities that could affect the value of your
dependent variable measurement). Outline how you will ensure variables
are kept constant and what your control will be.
Results
How will you present your results? Will you use a table? Will you
include photographs or draw a graph? Indicate if your results are to be
quantitative (measured) or qualitative (compared against each other).
Discussion
Did the product match the claims? Did anything bias your results or go
wrong? How could the method have been improved? Would you
identify the product as a solute, solvent, solution, colloid or suspension?
What evidence do you base this on?
Part 6: Good medicine
37
Conclusion
Did the product match the product’s claims? Why or why not? Use your
results with your explanation. Can you relate this information to
anything you have learnt in Lifestyle chemistry eg. solubility, skin pH or
skin microflora?
When presenting your report:
•
Remember to use scientific language in your investigation.
•
Don’t be afraid to include pictures, diagrams, graphs and tables and
information from other sources – these will often attract extra marks.
•
Refer to the Science Resource Book or contact your teacher if you’re
not sure how to approach the discussion and conclusion.
Good luck with your report!
38
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Bibliography
•
Lewis, R and Evans, W. 1997. Chemistry. Macmillan Foundations,
Hong Kong.
•
Sharwood, J. 2000. Nelson chemistry. Nelson Thompson Learning,
Melbourne.
•
Selinger, B. 1989, Chemistry in the Marketplace, Fourth Edition.
Harcourt Brace Jovanovich Group Pty Ltd. Sydney.
•
Barker, A and Knapp, K. 1983. Chemistry - a practical approach.
Macmillan Education Limited, Hong Kong
•
Garnett, P. 1992. Foundations of Chemistry. Pearson Education
Australia.
•
Noble, W. 1993. The Skin Microflora and Microbial Disease.
Cambridge University Press. Victoria. Australia.
•
Tannock, G. 1995. Normal Microflora. Chapman and Hall.
London.
•
Laidler, G. 1991. Environmental Chemistry – an Australian
Perspective. 2nd Edition. Pearson Education Australia.
•
Chemical Fact Sheets. ICI. Australia. Melbourne.
•
Orion Laboratories Pty Ltd. Western Australia. Material safety data
sheets. http://www.orion.net.au/ (accessed 4 July 2000).
•
Conte, U and Maggi, L. Geomatrix® system• for controlled release of
drugs. Department of Pharmaceutical Chemistry. University of Pavia.
Italy. <http://www.unipr.it/arpa/dipfarm/conf/abstracts/conte.html>
(accessed 20 June 2000).
•
Prell, G. Drug absorption, Distribution and Elimination. Mount
Sanai School of Medicine. City University of New York.
<http://www.mssm.edu/pharmacology/ParmCourse/Syllabus1998/>
(accessed 18 June 2000).
•
Gabard B, Elsneer P, Surber C and Treffel P. 1999.
Dermatopharmacology of Topical Preparations. A productdevelopment oriented approach. Springer-Verlag. Berlin.
Part 6: Good medicine
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40
•
Uno, H. The Histopathology of Hair Loss. Wisconsin Regional
Primate Research Centre. University of Wisconsin.
<http://www.npntserver.mcg.edu/html/alopecia/documents/>
(accessed 1 May 2000).
•
Nursing Times. 4/10/1973 Noble, W. Commensal bacteria of
human skin.
•
Theil, W J and Panagiotidis, J. Controlled Release Drug Delivery.
Department of Pharmaceutics.
<http://www.vcp.monash.edu.au/pharmaceutics/res-control.html>
(accessed June 17 2000)
Lifestyle Chemistry
Student evaluation
Name: ________________________
Location: ______________________
We need your input! Can you please complete this short evaluation to
provide us with information about this module. This information will
help us to improve the design of these materials for future publications.
1
Did you find the information in the module clear and easy to
understand?
2
What did you most like learning about? Why?
_____________________________________________________
_____________________________________________________
3
Which sort of learning activity did you enjoy the most? Why?
_____________________________________________________
_____________________________________________________
4
Did you complete the module within 30 hours? (Please indicate the
approximate length of time spent on the module.)
_____________________________________________________
_____________________________________________________
5
Do you have access to the appropriate resources? eg. a computer,
the internet, scientific equipment, chemicals, people that can provide
information and help with understanding science
_____________________________________________________
_____________________________________________________
Please return this information to your teacher, who will pass it along to
the materials developers at OTEN – DE.
SSCHSC 43168 Lifestyle chemistry
Learning Materials Production
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NSW Department of Education and Training