Name(s):
Period:
Date:
Determining Bonding Types
HASPI Medical Chemistry Lab
Background/Introduction
Electrolytes
How do you feel? No, really, how is it that when you touch something your
brain immediately knows something about it? The texture, the temperature,
even the size without even looking at it?
This is due to electrical impulses that pass through your body, known as an
action potential. This works because your neurons are full of electrolytes.
Electrolytes are any ion that dissociates in water, allowing the solution to
conduct electricity. Sodium, chloride, potassium and calcium ions are all
essential parts of this process. All along the neuron, specific electrolytes are
pumped on to either side of the cell membrane, and to send a signal,
electrolytes rush across the membrane, allowing the signal to move. The ion
pumps then re-set these ions so that the next signal can be sent.
http://www.bem.fi/book
/03/03.htm
http://webspace.ship.edu/cgboer/the
neuron.html
When you are low in electrolytes your body can’t communicate with your brain as well
and your muscles may cramp. You may feel more fatigue when you are low on
electrolytes. You might even crave salty foods, because table salt contains sodium ions,
which are a key component needed for nerve signals. Your sweat is full of electrolytes,
which is why you need to drink fluids rich in potassium, calcium and sodium when you
work out. Sports drinks also contain large amounts of sugar to help give you extra
energy when you drink them.
When a patient has diarrhea, one of the key things they lose is electrolytes.
For this reason, it is important to drink more than plain water when you have diarrhea,
because you need to replace your electrolytes to keep you strong. You also need to have
electrolytes to help you absorb water because your body absorbs water through osmosis,
which means that water follows the electrolytes. Pediatricians recommend that kids drink
Pedialyte when they are sick so that they get the right mix of electrolytes in their liquids, but
this works for any age. If you don’t have Pedialyte then you can use Gatorade or another
sports drink, however the large amount of sugar is not always a good idea when you’re sick,
so drink sports drinks in moderation or pick up some Pedialyte liquid or freezer pops!
http://canigivemyb
aby.com/pedialyte/
The Chemistry
Ionic, Covalent & Metallic compounds each have physical properties that relate to
their structures, so there are some tests we can do to help identify the type of
bonding in a substance.
Melting Points
An ionic bond is made when ions of opposite charges come together to create a
http://www.bbc.co.uk/schools/gcsebit
esize/science/add_ocr_21c/natural_en
crystal lattice structure. In order to melt an ionic compound the temperature has
vironment/hydrosphererev2.shtml
to rise until the ions move with enough force to break away from the oppositely
Student Handout – Pennium, an Isotopic Discovery, HASPI Medical Chemistry
1
charged ions around them. For table salt, this means you would need a temperature of 801°C to hit the
melting point (that’s over 1,000°F!).
Covalent compounds don’t break apart when they melt, so they only have to
reach a temperature strong enough to pull them away from the other molecules
to melt them. This is why most small covalent molecules are liquid or gas at room
temperature because they have such low melting points.
http://www.utdallas.edu/~brikowi/Teachin
g/Field_Methods/Lab_3_Background.html
http://zube.brinkster.net/SCH3U21/Reac
tions/Reading/stateparticles.jpg
Solubility & Conductivity
Ionic compounds dissolve very easily in water to create an aqueous solution.
Since water is a polar molecule (meaning it has partial charges) it attracts the
ions and surrounds each one as the compound dissociates in the water. Once
water is full of charged particles it can conduct electricity very easily. This is
why tap water conducts electricity the chemicals used to treat the water are
ions, so it makes the water into a conductor.
Non-polar covalent compounds do not dissolve well in water. They have
no charges on their outsides, so they are not attracted to the polar water.
Some polar-covalent compounds do dissolve well in water; however they
do not conduct electricity in the water because they do not have charges.
By testing a substance’s melting point, solubility and conductivity you
will be able to predict what type of bond it has.
https://chemistry11mrstandring.wikispaces.co
m/The+Conductivity+of+Aqueous+solutions
PreLab
Define the following terms on a separate sheet of paper
Electrolyte
melting point
Conductivity
Solubility
ionic
action potential
covalent
neuron
polar
1. List some examples of electrolytes.
2. What are two causes of low electrolytes?
3. List the expected physical qualities of an ionic
substance
4. List the expected physical qualities of a covalent
substance
Research these chemicals and fill out the data table
Ionic, Polar Covalent or Chemical Formula
Non-Polar Covalent
Paraffin Wax
Molar Mass
Medical Use
Fructose
Sodium
Bicarbonate
2
Student Handout – Pennium, an Isotopic Discovery, HASPI Medical Chemistry
Name(s):
Period:
Date:
Determining Bonding Types
HASPI Medical Chemistry Lab
Scenario
Today you will test substance A, B and C to determine which are paraffin, fructose and sodium
bicarbonate based on some of their physical properties. In the pre-lab, you researched these chemicals so
you know which one is ionic, which one is covalent, and which one is polar covalent.
As you complete each part of the lab, record your findings. At the end of the lab you will be asked to look
at your compiled data and determine the identity of each substance.
Safety
Wear your lab goggles and closed toed shoes at all times in the lab.
Part 1: Modeling
It’s important to understand what is happening at the atomic level when you are doing a lab. Think about
what you already know about each type of compound and draw what you think is happening. Use a pencil
so you can revise your drawing.
Draw an example of what you think an
ionic compound looks like at an atomic
level
Draw an example of what you think a
covalent molecule looks like at an
atomic level
Draw an example of what you think a
polar covalent molecule looks like at an
atomic level
Once you have drawn your models, discuss them with a partner. Look back over the prelab pictures and
see if you can gather more information from those pictures. Look in your notes or textbook to see if you
can refine your drawing to be more accurate.
Final Drawings:
Draw an example of what you think an
ionic compound looks like at an atomic
level when added to water
Draw an example of what you think a
covalent molecule looks like at an
atomic level when added to water
Draw an example of what you think a
polar covalent molecule looks like at an
atomic level when added to water
Student Handout – Pennium, an Isotopic Discovery, HASPI Medical Chemistry
3
Part 2: Melting Point
Look back to your pre-lab and think about which type of substance has a low melting point, which has a
very high melting point, then answer these questions to help you better understand what is about to
happen.
What kind of substance do you expect to melt first?
What kind of substance has a very high melting point?
Materials
Aluminum Foil
Step
1
2.
3.
4.
5.
6.
Hot Plate
Substance A, B and C
Small scoopula or ¼ tsp
Tongs
Procedure
Observations, Changes or Comments
Create a foil boat with 3 sections
Add ¼ tsp or small scoop of the each substance to
Note any differences in the three
different sections of your foil boat. Carefully wipe the
compounds
spoon out after each use to be sure no contamination
occurs but do not use any water.
Turn the hot plate to medium. Wait for your substances to melt. It they are not melting you can
turn the hot plate up.
When the first substance melts, record a 1 below.
Observations:
When the second substance melts, TURN OFF THE HOT
Observations:
PLATE and remove your foil boat using tongs. Record a 2
for the melting order
For the third substance you merely have to record that it
would melt 3rd. Do not attempt to melt it as the melting
point would be very high!
Data Table Part 2: Melting Points
Observations about the solid substance
Melting Order
Ionic, Covalent or
Polar Covalent?
Reasoning
Substance A
Substance B
Substance C
Part 3: Solubility in water
In the pre-lab you read that an ionic compound is very easily dissolved in water because the ions are
attracted to the polar water molecules and the compound will dissociate, or break apart, as it dissolves.
Polar covalent molecules are also fairly soluble because they are attracted to the water, although polar
covalent substances do not break apart as they dissolve. Non-polar covalent molecules are not soluble in
water because they are not attracted to the polarity of water, and they will either sink or float depending
on their density.
4
Student Handout – Pennium, an Isotopic Discovery, HASPI Medical Chemistry
Materials
Beaker A: Substance A in water
Step
1
2.
3.
Beaker B: Substance B in water
Beaker C: Substance C in water
Procedure
Pick up the first beaker labeled substance A in water. Write down
your observations. Do you see any solid remaining? Do you see any
liquid layers?
If the substance is fully dissolved, write SOLUBLE
If the substance is not dissolved, write INSOLUBLE
Repeat for remaining substances
Changes or Comments
Data Table Part 3: Solubility in water
Observations
Solubility
Ionic, Covalent or Polar
Covalent?
Reasoning for identification
Substance
A
Substance
B
Substance
C
Part 4: Conductivity
Look back at your pre-lab and think about which type of substance will conduct electricity. Do you expect
different results for each of the three substances? Which types of substances may have the same results?
Materials
Conductivity meter, Paper Towels, Pre-filled and labeled well plate with water, electrolyte solution, and
Substance A, B and C in water.
Step Procedure
Observations, Changes or Comments
1
Find your conductivity meter and turn it on. Look at the key on the back to see how you will
measure conductivity.
2.
Rinse the probes on the conductivity meter with DI water then dry them well. Now place the dry
probes into substance A. Record any conductivity.
3.
Use a paper towel to carefully clean the probes and ensure they are still dry. Now place the dry
probes into substance B. Record any conductivity. Repeat for substance C.
5.
You will now use the conductivity meter to test each What kind of bond does water have?
substance in an aqueous solution. Start by testing
the conductivity of pure DI water and the electrolyte What kind of bond do the atoms in the
solution
electrolyte solution have?
6
Use a paper towel to carefully clean off the probes on the conductivity meter. Now test each of the
substances, drying the meter between each test.
Student Handout – Pennium, an Isotopic Discovery, HASPI Medical Chemistry
5
Data Table Part 4: Conductivity
Conductivity in Ionic or covalent Reasoning
water
DI Water
Electrolyte
solution
Substance
A
Substance
B
Substance
C
Analysis & Interpretation
Compile your data from above to figure out which substance is which.
Analysis Data Table –Compiling & Interpreting Results
Melting Point
Order
Solubility
Conducts as a pure
substance?
Conducts when
dissolved in water?
Ionic, Covalent or Polar
Covalent?
Substance
A
Substance
B
Substance
C
1. What is the identity of substance A? What is your evidence and reasoning for this identification?
2. What is the identity of substance A? What is your evidence and reasoning for this identification?
3. What is the identity of substance A? What is your evidence and reasoning for this identification?
6
Student Handout – Pennium, an Isotopic Discovery, HASPI Medical Chemistry
Connections & Applications
Extensions:
Make your own conductivity meter:
http://scifun.chem.wisc.edu/homeexpts/CondTester/SolutionConductivity.htm
http://www.instructables.com/id/Conductivity-Meter/
Fructose Reading: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2467321/
Resources & References
References:
http://health.howstuffworks.com/wellness/diet-fitness/information/question565.htm
http://www.livestrong.com/article/268996-symptoms-of-low-potassium-of-electrolytes/
Images:
http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_21c/natural_environment/hydrospherere
v2.shtml
http://www.utdallas.edu/~brikowi/Teaching/Field_Methods/Lab_3_Background.html
http://zube.brinkster.net/SCH3U21/Reactions/Reading/stateparticles.jpg
http://webspace.ship.edu/cgboer/theneuron.html
http://www.bem.fi/book/03/03.htm
Student Handout – Pennium, an Isotopic Discovery, HASPI Medical Chemistry
7