Poly Vinyl Alcohol and Borax a High
Viscosity Solution A.K.A
Chemistry Department
Outreach Team.
Chemistry Of Slime
Slime has properties of both solids and liquids. It can be torn like a
solid but can also mould to the shape of it’s container.
Borate ions fit perfectly with the
hydroxyl groups on the polymer chains.
This process traps water within the 3D
lattice structure. The water constantly
evaporates keeping the slime cool.
Slime Viscosity
It can be made using
Poly Vinyl alcohol (PVA) and
Borax. Borax slowly creates
cross links between two PVA
polymer chains using weak
hydrogen bonds. This creates
a semi-rigid 3D lattice
structure.
Natural Slimes
H3C
CH3
HO
OH
HO
OH
B
HO
HO
-
OH
OH
OH
OH
Weak Hydrogen
Bonds
OH
OH
OH
OH
OH
OH
B
OH
H 3C
3ml
OH
OH
OH
C H3
Distance travelled by slime after 10 minutes
2ml
OH
-
The more Borax we add, the more cross links are formed between
the polymer chains, this makes the slime more viscous. Because of
this, slime containing more Borax (4ml) barely moves in 10
minutes, whereas the slime containing the least Borax (1ml)
reaches the bottom of the container.
1ml
Fish are very slimy
creatures, they use
their slime to regulate
body temperature and
to act as a barrier
against parasites and
germs.
OH
HO
HO
OH
OH
Slime occurs in nature and is also used synthetically. Snails and slugs are the
most commonly encountered slimy land based animal using slime to help
them move.
4ml
Poster produced by Year 10 Work Experience students between July 6th – 10th 2009
‘Killing’ Slime
The bonds formed when slime
is made are weak so when
acid is added they are easily
broken. The Borate associates
with acid instead of the
hydroxyl groups. The cross
links are destroyed and the
slime ‘killed’- becomes liquid.
Adding base to this liquid
neutralises the acid and
allows the Borate to reassociate with the polymer
chains. The slime is revived!
This process can be repeated
several times.
Olivia Sweeney
Waingels school
Universal indicator was
added to the slime to
monitor changes in the pH.
Piotr Gorski
Highdown School
My work experience week at Reading University chemistry department.
Chemistry Department
Outreach Team.
Harriet Wilkinson Highdown School and Sixth Form Centre, Reading 2008
During the work experience week in the chemistry department, I was responsible for the preparation of an iodine clock reaction. This was
going to be tested by a group of local A' level chemistry teachers as part of the departments chemistry demonstration evening on the
Wednesday evening - so no pressure there then !
I made four different solutions, each to a specific
concentration, by using my new found knowledge of what a
mole is. If I didn’t get the measurements correct, then the
experiment wouldn’t work. I used these solutions to prepare
five of the iodine clock reactions. These varied in size from
100 mL to 2 L The reaction systems had to be tested to
ensure that the time for the blue iodine colour to appear was
constant.
During the testing of this experiment, we found that the
mixture of chemicals could not be prepared and left to stand,
as this effected the time it took for the solution to turn
blue/black.
Preparing and testing the clock reaction
Success - it works for the teachers
Luckily, when the teachers performed their test, each solution
turned blue/black within seconds of each other.
This demonstration shows that it is the
concentration, and not the quantity of a substance
which is important in determining how long a
reaction will take.
Mixing chemicals was not all I did during this week, I also got the chance to visit the analytical equipment here at the University. I found this really
interesting and it amazed me that technology is so advanced and you can view things in such great detail. I had a great week at the University. I learnt lots
of new things and it was a really good work experience.
Some of the other interesting demonstrations prepared for the teachers.
Balloon tortureholding a balloon
over a candle
flame and it
doesn’t pop!
Plus some spectacular
reactions:
The visualisation
of convection
currents in a
large 10L beaker
aluminium and iodine
potassium permanganate
and glycerol (note the lilac
flame colour).
Aspirin synthesis for AS/A2 Level chemistry.
Chemistry Department
Outreach Team.
Charlie Archer, The Oratory School, Reading, 2008
Aspirin is one of the most commonly used drugs in the world, so why not bring chemistry out of the text books, and synthesise aspirin in the
undergraduate chemistry laboratory at Reading University. Using familiar A' level chemistry, you will produce aspirin using an esterification reaction
with ethanoic anhydride. The starting material, for this synthesis, is 2-Hydroxybenzoic acid (salicylic acid)., Salicylic acid is the naturally occurring
analgesic, that can be extracted from willow bark, but is very bitter and less effective than aspirin.
O
OH
O
H 3C
O
OH
+
[H ]
O
O
H 3C
+
O
O
O
cat
OH
Reflux
+
H3C
OH
H 3C
2-hydroxybenzoic acid
salicylic acid
The reaction
The aspirin is formed when you reflux
ethanoic anhydride, phosphoric acid,
and 2-hydroxybenzoic acid together for
15 minutes. Quenching the reaction
mixture with cold water forces the crude
aspirin out of solution. This crude aspirin
can then be isolated by filtration.
aspirin
2-(acetyloxy)benzoic acid
Re-crystallisation
The crude aspirin obtained, is
purified by re-crystallisation from
a minimum volume of hot
aqueous ethanol. The pure aspirin
crystals formed are separated and
dried by vacuum filtration
ethanoic anhydride
2-(acetyloxy)benzoic acid
acetic anhydride
Testing the product
The purity of your aspirin sample
can then be assessed by using
both: thin layer chromatography
(TLC), with visualisation by U.V.
and determination of its melting
point.
What the students thought about the aspirin synthesis:
“Very interesting and fun to do”
“We used different types of equipment not available at school”
“It showed the usefulness of chemistry in real-life
situations”
aspirin
ethanoic acid
acetic acid
The pure aspirin
At the end, the
teacher may be
on their knees,
but they’re
still smiling.
Extraction of the Essential Oil Limonene from Oranges.
Chemistry Department
Outreach Team.
Ahmed Saleh, Denefield school, Reading 2008
The Distillation
Steam Distillation of Orange Peel
Low molecular weight water
immiscible compounds can
be separated from natural
products by steam
distillation. In this case steam
distillation is used to isolate
the essential oil limonene
from the orange peel.
Extraction of Limonene from the
Distillate
Initially an oily water / limonene mixture can be
seen condensing on the glassware at a
distillation temperature of 98 C. The
temperature will rise to 100oC as the distillate
composition approaches pure water.
The lower layer is the
remaining aqueous distillate
Limonene is concentrated in the peel of an
orange. The orange peel has two distinct layers,
the skin and the pith. Limonene Is not distributed
evenly between these two layers. Experimentation
has shown that only minimal quantities of
limonene can be extracted from the white pith.
Pith
Skin
Mass of Orange Peel
Limonene’s structure
This outer skin
accounts for two –
thirds of the mass
of the peel. The
best yields of
limonene are
obtained by using
only this outer skin.
The yield of limonene is about 1% using this
outer skin. This is a large yield compared to
other essential oil extractions, where yields
can range from 1-0.01 % by mass.
Orange peel cut into small pieces,
placed into 100 mL of water
Evaporation of the Solvent
Limonene can be
observed as an
oily suspension in
the final distillate
(80 mL).
Heat
Essential oils can be steam distilled from flowers, leaves, fruits, barks and woods
Essential oils are
found in many
household products,
ranging from high end
cosmetics to basic
cleaning materials.
Lavender
Patchouli
Limonene, an alkene, is
extracted into a low density
water immiscible solvent (ether).
Bergamot
Cinnamon
To finalise the
extraction, the ether
layer (b.pt. 37oC)
was evaporated on
a water bath to
leave the limonene
(b.pt. 176oC).
limonene (150mg)
obtained from 15 g
of orange peel skin.
The limonene has
an intense aroma of
oranges
The Emmbrook
Looking into invisible
Chemistry Department
Outreach Team.
Adam Young and Toby Parrott. Year 10 The Emmbrook 2009
Invisible inks have been used as a means of communicating secret messages for hundreds of years. These inks have been valuable for a wide range of uses, including
espionage, anti- counterfeiting, property marking, children’s games, within manufacturing and many more. There are many different methods available, and selecting the
right one is vital to the success of any secret communication.
The Chemical reveal
The heat reveal
Throughout history secret messages often needed to be
revealed rapidly and without arousing suspicion. For this
reason Invisible inks would often need to be written and
revealed with easily obtainable materials. A variety of
household products were tested for their suitability as
invisible inks and charring was used to reveal the messages.
Invisible
Some methods use reactions between the ink and another chemical to
develop the message. 1. Due to the pH of some inks, indicators can be
used to produce a colour change 2. The ink may simply react with
another chemical to give a coloured compound. Using an indicator,
particularly Phenolphthalein, with Ammonia gives excellent invisibility
and is non-permanent when revealed, making it an ideal method.
UV Visibility
UV visualised inks are commonly used today,
especially for security purposes. When using these
inks it is vital to take consider the paper used, as
many modern papers use optical brighteners,
which fluoresce under UV light.
Revealed
Tonic water
Persil detergent
Milk
Modern uses of invisible inks include security markings
on bank notes, passports and driving licenses.
The chemicals in the ink burn
at a lower temperature than
the paper, however, this can
easily lead to the paper
burning so heating must be
gentle!
Red cabbage can be used as an
indicator to reveal some acidic and
basic inks, however, ammonia, citric
acid and acetic acid proved
unsuccessful, with both the modern
and chromatography paper.
Determining Vitamin C levels in fruit using iodine titrations.
Chemistry Department
Outreach Team.
By Joshua Grant & Jacob Jolly
Natural sources of vitamin C
Plant source
Kakadu plum
Camu Camu
Rose hip
Acerola
Sea buckthorn
Jujube
Indian gooseberry
Baobab
Blackcurrant
Red pepper
Parsley
Amount
(mg / 100g)
3100
2800
2000
1600
695
500
445
400
200
190
130
What is vitamin C ?
Testing whole fruit
Vitamin C, also known as L- ascorbic acid, is
an essential nutrient to humans . The vitamin
protects the body from oxidative stress and
prevents scurvy. Plants can make it
themselves as can some animals, but humans
do not have the right enzyme.
In our diet citrus fruits are a
common source of Vitamin C
Filtering the liquidised
mixture
Testing fruit juices
Method
10 cm3 of each fruit juice was
pipetted into a conical flask
with 1 cm3 of starch indicator
solution. Each mixture was
titrated with iodine solution.
Cranberry juice
Iodine reacts with Vitamin C.
Initially no colour change is
seen. When all the Vitamin C
has reacted adding more
iodine gives an excess and the
cranberry juice turned purple.
Tropical juice
On titration with iodine the
tropical juice/ starch mixture
turned a dirty brown colour due
to the colour of the orange
juice mixing with the blue/
black colour of the iodine.
A known mass of fruit
was liquidised in a
measured volume of
water.
The liquidised sample
was filtered and the
filtrate titrated with
iodine solution.
Among the fruits tested
were apple, lime,
Grapefruit and
Oranges.
Fruit extract Vitamin C levels
per gram of fruit.
3.0
A titration
Fruit juice Vitamin C levels
2.5
25.00
2.0
20.00
1.5
15.00
1.0
10.00
0.5
5.00
0.0
0.00
Apple
Tropical Cranberry Tropicana Co-Op
Orange
The results: Unbranded orange juice was
found to have more vitamin C than the top
brand Tropicana orange.
Lime
Grape Orange
fruit
The results: For the whole fruits we tested
Grape fruit showed the highest levels of
vitamin C in it its extract.
Schools Analyst Competition 2009
Solvent a
K=
Solvent b
[NH3]a
[NH3]b
x
x
Then applying Beer-Lambert’s Law they
determined the concentration of the orange food
colouring in Irn-Bru using visible spectroscopy.
Comparing the value they obtained to the
manufacturer’s own stringent specification.
X
Absorbance
The first involved the determination
by
titration
of
the
distribution
coefficient (K) for ammonia between
two immiscible solvents.
Standards
Reading University hosts a South
East regional heat for 16 teams of
three students. The winning team from
the regional heats being entered into
the national final. The Reading heat
consisted of two tasks.
The second task was in
two stages. Initially the
teams
used
thin
layer
chromatography to identify
the orange food colouring
used in Irn-Bru. This was
achieved by comparison to a
given set of standard food
colourings.
Irn-Bru
The Schools' Analyst Competition
is a national competition run by the
Royal
society
of
Chemistry’s
Analytical Division, for first year sixth
form students studying AS level
Chemistry or equivalent.
A = Log
It
Io
X
X
X
X
Io
Source
X
It
Detector
Sample
Concentration
This years winners were:
Abingdon school
Abingdon
They will be representing the
Southeast region, in the national
final at The University of Plymouth.
Chemistry Department
Outreach Team.
2009
Chemistry Department
Outreach Team.
Salters’ festivals of Chemistry promote the appreciation of chemistry to young students and give them the opportunity to spend a day in a university
department. These activities are followed by a fun lecture and prize giving ceremony. Prizes are awarded to the winning teams in each challenge.
This year at Reading University, 15 Schools competed against each other in two exciting practical chemistry challenges.
The University’s Challenge:
The SALTERS’ Challenge:
Cool it ! on the Enterprise
Murder (?) at Saltmarsh Farm
In order to prevent the dilithium crystals aboard
the starship Enterprise from being destroyed,
the teams had to devise a chemical method to
cool the crystals to exactly 10.5oC in 1.5 minutes.
In this activity teams took on the role of forensic
scientists, and used chemical techniques to analyse
evidence collected from the scene of a grisly crime.
Their task was to identify the prime suspects.
Close scrutiny of the university challenge was the order of the day
Accuracy and precision were key as pupils examined the evidence
In the afternoon, teams were entertained with an exciting demonstration
lecture by Dr David Watson (Reading University). The lecture explored
temperature and featured dry ice (solid CO2 -78oC) and liquid nitrogen
(-196oC) - not forgetting the balloons, bananas, Blu-Tac and ice cream !!
Members of this years’ winning teams in action.
Salters’ Challenge:
Queen Anne’s school, Caversham
No shortage of volunteers – to taste Dr Watson’s Ice cream
Thanks to Parniyan Salar and Anne Romero, Reading Girls’ School 2009 work placement students for their help with this poster.
University’s Challenge:
The Abbey School, Reading
Preparation of a ferrofluid for AS/A2 students.
Chemistry Department
Outreach Team.
Francesca Churchhouse, The Piggott School, 2008
Synthesis of nano-sized magnetite
2FeCl3 + FeCl2 + 8NH3 +4H2O
Iron (III) chloride
Fe3O4 + 8NH4Cl
Iron (II) chloride
Magnetite
A ferrofluid is a stable colloidal suspension of magnetite nano-particles. These nano-particals (1 to 30 10 -9 m) become strongly polarised in the presence of a magnetic field. This
gives the ferrofluid the appearance of a ‘solid’, but they revert to their liquid state when the magnetic field is removed. NASA has exploited this technology to manipulate fluids in the
low gravity environments encountered in space.
Oleic acid (0.5ml) is
added to the magnetite
suspension and the
mixture heated to 90 C.
Green
Ferrous Chloride
As the oleic acid is
adsorbed onto the
surface of the nanoparticles, the surface
becomes considerably
more hydrophobic.
Brown
Ferric Chloride
Add the FeCl3 solution (2 ml 2 M,
in 2 M HCl ) to the stirred FeCl2
solution (1 ml 2 M, in 2 M HCl) at
room temperature.
Slowly, over 5
minutes, add NH4OH
solution (13 ml 2 M)
using a burette.
An initial brown
precipitate turns black
as the magnetite nanoparticles are formed.
Stabilisation of magnetite nano-particles with a surfactant.
This causes the nano-particles to ‘precipitate out’
of the aqueous phase. Clear aqueous phase is
visible when the nano-particles are attracted to a
magnet.
The ammonia is
vapourised, and the oleic
acid binds to the surface
of the nano-particles.
Interaction of the ferrofluid with a
magnetic field.
Oleic acid
(Z)-octadec-9-enoic acid
Before the addition of
the oleic acid the
synthesised
magnetite nanoparticles are
suspended in the
aqueous phase but
are ‘insoluble’ in
decane.
Decane
Aq.
Magnetite
10-30 nm
Agglomeration of these
nano-particles will occur
over time, if no
surfactant is added.
This will give
aggregates in the m
size range. These
larger particles will not
act as a ferro fluid.
Nano-particles
are susceptible
to agglomeration
Aggregate particle size >> 1.0 m
Addition of oleic acid
causes the nano-particles
to be stabilised by less
favourable interaction
between the hydrocarbon
tails of the surface bound
oleic acid.
Unfavourable
hydrocarbon
interactions
Picture 1 - The decane
based ferrofluid is a low
viscosity liquid.
These hydrocarbon tails
enables the oleic acid
stabilised nano-particles
to be readily extracted by
organic solvents.
Picture 2 –However, in the
presence of a magnetic field
the ferrofluid is constrained
and no longer free flowing.
1
Decane
10-30 nm
water
2
Picture 3 - Shows a
commercial ferrofluid in
the presence of a very
strong magnetic field, -impressive spikes form
inline with the magnetic
field.
3
Justice is not always black and white.
Stephen Penney, Little Heath School and Jack Stanford, St. Crispin‘s school - work placement 2009
Chemistry Department
Outreach Team.
It was not until the early 1900’s that the United Kingdom Fingerprint Bureau was founded at Scotland Yard, where they pioneered the use of fingerprints in
criminal investigations. Since then, forensic scientists have worked continuously to develop the technology behind fingerprint visualisation.
Fingerprint powders come in ‘all’ colours.
Developing a latent fingerprint.
Grease, oil and sweat from fingers are transferred
to the surface being touched. This leaves a latent
print, mirroring the ridge pattern present on the
finger. Latent prints can be barely visible. They are
made visible by dusting with very fine powders.
Evidence found at the scene of a crime is not always white. Forensic scientists have developed
a wide range of different coloured fingerprint powders. The powder is chosen to give the best
contrast between the print and the background. This contrast can be enhanced by irradiation of
the fluorescent fingerprints with ultra-violet light.
Fluorescent green
Powder Adsorption
Mechanisms
Metallic Gold
on glass
Fluorescent green
under UV light
Held in place by
surface tension
Fluorescent
red
Static charge attracts the
powder to the latent print.
Oily deposit left behind on a non-porous surface
The powder binds to the oils and sweat of the latent finger
print, but not to the underlying surface. This makes the
unique ridge pattern of the fingerprint visible.
Types of fingerprint ridge pattern.
Fingerprint patterns can be categorised into 3 main types.
The most frequently encountered being Loops (60-70%).
Whorls account for 25% and are subdivided further into:
double loops, plain and central pockets. The final type,
Arches, are the rarest accounting for only 5%.
Fluorescent red
under UV light
Evidence comes in all shapes and colours, with a powder for each!
One powder two colours ?
Loop
Whorl
Double Loop
Arch
Classic black on white
fingerprints.
These two prints have both been dusted
with the same bi-chromic powder. The
fingerprints appear dark on a light surface
and metallic on a dark surface.
bi-chromic powder fingerprints
Joseph Reed
The Piggott School
Synthesis of the Analgesic: Lidocaine
Chemistry Department
Outreach Team.
Lidocaine is a common local anaesthetic used to relieve pain and itching, injected in dental surgery and used for minor operations. Lidocaine can be synthesised
from 2,6-dimethyl-nitrobenzene [1] in three consecutive reaction steps: The first is a reduction, converting the nitro group into an amine. The second converts
this amine to an amide. The final step involves the substitution (SN2) of a alkyl halide substituent by an amine to give the target compound lidocaine.
Step 1- Nitro Reduction
2,6-dimethylnitrobenzene [1] is
reduced by stannous chloride,
Sn(II)Cl2 in acidic conditions to
form the aniline hydrochloride
salt. The initial product, 2,6dimethylaniline [2] is liberated
as an oil, on treatment of this
salt with a base (pH 10-12).
ON+
O
H
Step 1 Reduction
H
Step 2- Amide bond [3] formation
-
N
O
O
(i) SnCl2/HCl/CH3COOH
(ii) KOH
R1
70%
2,6-dimethylnitrobenzene
[1]
2,6-dimethylaniline [2]
Step 2 Amide Formation
The rotary evaporator
CH3COOH
70%
(i) ClCH2COCl
(ii) CH3CO2Na
Step 3 Substitution
H
(CH3CH2)2NH
N
ΔR Toluene
41% crude 21% pure
Lidocaine [4]
Cl
+
Base
The amine group (NH2)
acts as a nucleophile,
attacking the carbon of the
polarised carbonyl group in
the acid chloride.
This gives a tetrahedral
intermediate which breaks
down to form the new
amide [3] and release a
chloride ion.
Cl
H2N
R1
R
O
Cl
HN
-
R1
R
Lidocaine
Cl
O
Chloro-2,6-dimethylacetanilide
2-(diethylamino)-N-(2,6-dimethylphenyl)-acetamide
The rotary evaporator
removes solvents at a low
temperature by heating
the solution under a
vacuum. In addition the
solution is rotated in the
flask to increase
efficiency. In the flask is
the 2,6-dimethylaniline [2]
which was isolated using
a rotary evaporator.
‡
[3]
Step 3- SN2 Substitution of an alkyl halide.
The amine attacks the polarised C-Cl bond at the carbon. The C-Cl bond breaks as the new
N-C bond forms. The chloride ion released can deprotonate the nitrogen of the amine to
generate Lidocaine and hydrochloric acid.
The overall yield for the three
stages was 17.9% crude and
8.7% re-crystallised. The final
step gave the lowest yield.
This step requires further
optimisation.
Analysis of the final product by accurate mass
spectroscopy, showed that a very pure sample of
lidocaine had been synthesized.
C14H22N2O
R3
H
R4 N
H
H
Cl
R4
‡
R3
Cl
H
Acc. Mass:
234.3406
Det. Mass:
235.1799
R3
H + HCl
H
H
SN2 intermediate
Special thanks to Reading School pupils; Adam Wright, Daniel Rowlands & Alex Brown: for their help with the Lidocaine synthesis.