Chemical Bonds
Process objectives: 1. To analyze data and rank substances according to melting points.
2. Observe compounds for solubility or insolubility.
Learning objectives: match ionic and covalent bonds to types of compounds.
Introduction:
Chemical compounds are combinations of atoms held together by a type of chemical bond.
These bonds may be ionic or covalent. Ionic bonds result when one or more electrons from one atom
or group of atoms are transferred to another atom. Positive and negative ions are created. In
covalent compounds the electrons are shared by the bonded atoms.
The curls and waves of your hair are the result of the many ionic, covalent and hydrogen
bonds between the chains of atoms that make up each hair follicle. Hydrogen bonds are the result of
hydrogen atoms being attracted to unshared pairs of electrons on other compounds. Styling hair by
wetting it or heating it with a curling iron is an attempt to change the hydrogen and ionic bonds so
they will form a desired shape. The changes are temporary, and as soon as you wash your hair, the
style is gone. The solutions in a “permanent,” however, break and reform the covalent bonds. A
permanent wave does not wash out when you shampoo your hair.
The physical properties of a substance such as melting point, solubility, and conductivity tell us
a lot about the type of bond in a compound. In this experiment you will conduct tests on these
properties and compile data enabling you to classify compounds as ionic or covalent.
SAFETY
Take the necessary precautions before beginning this experiment. Wear safety goggles, and
apron. Read all safety cautions, and discuss them with your teacher. It is important to use
good safety techniques while conducting experiments.
Apparatus
Tin can lid
2 thin stem pipettes
Marker
Materials
Sucrose
Sodium chloride
iron ring stand and ring clamp
conductivity apparatus
Phenyl salicylate
Calcium chloride
Potassium iodide
Citric acid
24 well microtitration plate
Bunsen burner
ethanol
Procedures
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Procedures
1. Draw the safety symbols in the appropriate places before starting the lab. Get approval from your
teacher before you start.
2. Record a brief description of each substance in your Data Table.
3. Set up the ring stand and clamp. Do NOT light the Bunsen burner yet! Make sure to follow the
three finger rule.
Caution: Before lighting the burner, check to see that loose clothing and long hair have been
confined.
4. Obtain a tin can lid, and label 6 spots. Place a FEW crystals of sucrose in spot 1, a FEW crystals
of sodium chloride in spot 2, a FEW crystals of phenyl salicylate in spot 3, a FEW crystals of calcium
chloride in spot 4, a FEW crystals of citric acid in spot 5, and a FEW crystals of potassium iodide in
spot 6. Do not allow the samples of crystals to touch.
5. Light the burner, and watch carefully. Some of the samples may not melt. Do NOT let the burner
run for more than 2 (two) minutes. Record the order of melting in your Data Table. Record an “n” for
any substances that do not melt. Allow the lid to cool while completing the rest of the experiment
6. Take the microtitration plate, and make sure that the row of 6 (six) wells is horizontal. Put a FEW
crystals of sucrose in well 1, a FEW crystals of sodium chloride in well 2, a FEW crystals of phenyl
salicylate in well 3, a FEW crystals of calcium chloride in well 4, a FEW crystals of citric acid in well 5,
and a FEW crystals of potassium iodide in well 6. Repeat this procedure in the second row of wells.
7. Add 10 drops of distilled water to the top row. Record the solubility of each substance in the Data
Table. You may want to stir each well with a different toothpick to be sure it is/not soluble. Use “Y”
for soluble, and “N” for not soluble.
Caution: Ethanol is flammable. Be sure all burners are extinguished before you begin.
8. Add 10 drops of ethanol to each well in the second row of the microtitration plate. Record the
solubility of each substance in the Data Table. Use “Y” for soluble, and “N” for not soluble.
9. Test the conductivity of each water solution by dipping both electrodes into each well of the
microtitration plate. Be sure to rinse the electrodes and dry them with a paper towel after each test.
If the bulb of the conductivity apparatus lights up, the solution conducts electricity. Record “Y” or “N”
in the Data Table.
10. Clean the microtitration plate by rinsing it with water. If any wells are difficult to clean, use a
cotton swab. Clean the tin can lid by rinsing it with water, and drying it with a paper towel. Leave
these pieces of equipment out for the next hour.
11. Define Soluble:_____________________________________________________________
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Data Table
Description
Melting Solubility
Conducts
Order
water ethanol
________________________________________________________________________________
1.Sucrose
________________________________________________________________________________
2.Sodium chloride
________________________________________________________________________________
3.Phenyl salicylate
________________________________________________________________________________
4.Calcium chloride
________________________________________________________________________________
5.Citric acid
________________________________________________________________________________
6.Potassium iodide
________________________________________________________________________________
Questions
1. Group the white substances into two groups according to the properties you find useful. Give a
reason for each group.
2. Explain how you can group elements when sometimes all the elements in a group do not exhibit
exactly the same properties.
3. Identify which group is ionic and which group is covalent.
4. Summarize the properties of ionic and covalent compounds
5. Why don’t permanents wash out of your hair?
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright