DAY 6
CONDUCTIVITY AND
CHEMICAL BONDING
Name_______________________________
In this experiment, you will measure the conductivity of several different compounds and solutions in
order to predict the bond type (ionic or covalent) in the substances tested. To understand conductivity, we
must first define electric current. An electric current is produced by the motion of positive or negative
particles. An electric current is measured in terms of the total number of positive or negative charges
passing a given point per second. In a solid, such as wire, only the negative charges (free electrons) are
able to move. Conductivity is a property that describes the ability of a substance to transmit an electric
current.
Experimentation has shown that pure water is a very poor conductor of electricity. The poor
conductivity of water can be attributed to its molecular bonding. When solid sodium chloride, an ionic
solid, is added to the water, a conducting solution is formed. The salt water solution is a good conductor
because the NaCI forms Na+ and CI- ions in solution. These ions migrate toward oppositely charged
electrodes. The moving ions complete the electric circuit. You can predict bond type in some solids by
dissolving some of the solid in water and measuring the conductivity of the resulting solution.
Objectives
In this experiment, you will
• test a number of different substances and solutions for their ability to conduct an electric
current, and
• predict the bonding nature of each substance, on the basis of your results.
EQUIPMENT
goggles and apron
conductivity apparatus
beakers (100 or 150 mL)
Solid-partially fill beaker with crystals. Test for
conductivity (see Step 4). Retain a small
amount for further testing; return the remainder
to the appropriate container.
PROCEDURE
1. Safety goggles and lab apron must be worn for this
experiment.
2. Support the conductivity apparatus as shown in
Figure 20-1. (As there are many types of conductivity
set-ups available, your teacher may provide one that
is not the same as the one pictured here.) CAUTION:
Dilute Water Solution-add a few crystals of
solid to 30 mL of distilled water.
Water Solution-add about 1 g of solid to 30
mL of distilled water.
Alcohol Solution-add about 1 g of solid to
30 mL of alcohol.
Acetone Solution- about 1 g of the solid to 30
mL of acetone.
CAUTION: Alcohols and acetone can be poisonous
There is danger of electrical shock; apparatus must be
turned off when placing it in or removing it from sample.
3.Obtain one of the compounds and prepare (one at a time)
the solutions listed in the table. Listed to the right are
general directions for each test condition. Use 100 or 150
mL beakers.
through skin absorption or inhalation. They are also
highly flammable. Keep away from flames; avoid
skin, eye, lung contact.
.
To test for conductivity lower the electrodes into the 4
material in the beaker. Rate the conductivity of each
test material as good, poor, or none. Record your
rating and any other observations.
The pure alcohol and all solids should be returned to
the reagent table. All water solutions may be rinsed
down the drain using plenty of water.
Test Material
Distilled water
Conductivity
Other Observations
Tap water
Alcohol – See CAUTION above
Acetone – See CAUTION above
NaCl solid
NaCl dilute water solution
NaCl water solution
NaCl alcohol solution
NaCl acetone solution
Sucrose solid
Sucrose water solution
Sucrose alcohol solution
Sucrose acetone solution
CaCl2 solid
CaCl2 water solution
CaCl2 alcohol solution
CaCl2 acetone solution
CONCLUSIONS
Answer the following using complete sentences on a separate piece of paper
1. Explain the similarities and differences in your conductivity results for NaCl and CaCl 2.
2. What was the purpose of using both water and alcohol as solvents?
3. Explain any differences in your results for distilled and tap water. Why is it important that laboratory solutions are
made with distilled water instead of tap water?
4. On the basis of this experiment, what conclusions can you draw concerning the bonding in the four solids tested?
5. What effect does concentration of a solution have on its conductivity?