Experiment 8 – Electrical Conductivity and Chemical Bonding
INTRODUCTION
Electricity was discovered even before John Dalton set forth the modern concept of the atomic
nature of matter. The observation that electricity can travel through matter such as wires suggests
that matter might be electrical in nature. In fact, later in the 19th century, scientists by probing the
nature of electrical beams were able to demonstrate that atoms of all elements are composed of
electrically charged particles called protons and electrons.
For an electric current, there must be a flow of charge. In solid conductors such as copper wire
which have metallic bonding, some electrons are held very loosely in the d sub-orbitals and are
relatively free to flow. A current, however, does not consist of continuous movement of the same
electrons, but is more like a domino effect where one electron moves a short distance before colliding
with and transfering its energy to the next electron. Once this electron domino effect is set in motion
by an energy source such as a battery or a generator, the flow continues with only a little resistance in
metals. Nonmetals do not have loose electrons. They impede electron flow and are electrical
insulators.
Passage of a current through a solution occurs in a rather different way. Pure water only conducts
very slightly but aqueous solutions containing ions can be good conductors. For conduction to occur
in solution, cations must migrate to the negative electrode (cathode) and accept electrons while
simutaneously anions migrate to the positive electrode (anode) and deposit electrons. The net result
of the double migration is a flow of electrons from the anode to the cathode and completion of the
circuit. More dissolved ions allows for a greater flow of electrons.
Generally, only two types of compounds will dissolve in water. These are many ionic compounds
and some covalent compounds. When ionic compounds dissolve in water, dissociation occurs, forming
aqueous cations and anions. Dissociation is the separation of the positive and negative ions in an ionic
compound:
NaCl(s)  Na+(aq) + Cl-(aq)
If an ionic compound dissociates (dissolves) sufficiently in water, then the solution will conduct
electricity and the compound is called an electrolyte. The dissolving of covalent compounds in water
does not normally result in the formation of ions except for certain acids and bases.
In this experiment, you will study the conductance of several solutions to determine if the type of
bonding present in the compound is ionic or covalent. In addition to studying the conductivities of solids
and aqueous solutions containing single compounds, you will do some studies monitoring conductivity as
a second solution is added.
PRE-LAB QUESTIONS
1. Name the four compounds for which no name is given in the directions below except for NH3. NH3 is
named ammonia.
a.
c.
b.
d.
2. Which will cause higher conductivity: more dissociation or less dissociation? How do you know?
PROCEDURE
1. Study the back of the conductivity apparatus to discover the relationship between the
brightness of the red and green lights and conductivity.
2. Using the conductivity apparatus provided, test the conductivity of the solids.
3. Using the digital Vernier conductivity probe, compare the conductivity of the solutions.

Be VERY careful not to cross-contaminate any of the solutions!

Make sure the Vernier meter is set to 200 μs/cm.
RESULTS:
Material
aluminum
copper
glass rod
carbon (graphite/pencil
lead)
plastic strip
silicon
wood splint
0.1 M NaCl
0.01 M NaCl
0.001 M NaCl
distilled water
tap water
0.1 M glucose
0.1 M ethanol
0.1 M NaOH
0.1 M NH3
0.1 M HCl
0.1 M HC2H3O2
Observations & Conductivity
QUESTIONS
1. Compare the conductivities observed for the solid substances.
a. Everyone knows that metals conduct electricity and nonmetals do not. Does your data
support this statement? Were there any exceptions to the rule? If so, which solid(s)?
b. What did the metalloid do?
2. Compare the conductivities observed for the three different concentrations of NaCl (aq). Which
has more dissolved ions? How do you know?
3. What do your results for distilled water and tap water tell you about the dissolved ions present
in each?
4. Compare the conductivities for 0.1 M NaCl, 0.1 M glucose and 0.1 M ethanol.
a. Which one contains the most dissolved ions?
b. Which one(s) are unlikely to contain ionic bonds?
5. Compare the conductivity of 0.1 M NaOH versus that of 0.1 M NH3 (both are bases). Which
solution contains more dissolved ions?
6. Compare the conductivity of 0.1 M HCl versus that of 0.1 M HC2H3O2 (both are acids). Which
acid dissociated the most?
7. Acids that dissociate completely are called strong acids. Acids that do not dissociate completely
are weak acids. Between HCl and HC2H3O2, which is a strong acid and which is a weak acid?