Lab Investigation: Comparing Ionic and Molecular Substances
Purpose: To determine the solubility in water of ionic and molecular substances
and well as the conductivity.
Introduction: An electrolyte is a material that contains free ions that can
conduct electricity. Substances will be tested by a conductivity tester to see
whether or not electricity is conducted or not, when they are mixed in water.
Basically this experiment is based on whether ionic and molecular substances
given, mixed with water could conduct electricity.
Hypothesis: If the ionic substances are mixed with water then electricity will be
conducted somewhat or fully, depending on which substance is used. If
molecular substances are mixed with water, then electricity will not be
conducted.
Station Materials:
 Watch glass
 Stir rod
 Conductivity tester
 Sample beaker
 Wooden splint
 Distilled water bottle
 Waste beaker
 Tissue paper
Ionic Substances:
 Salt (NaCl)
 Potassium Chloride (KCl)
 Copper (III) Sulfate (CuSO4)
Molecular Substances:
 Simple sugar (gulucose)
 Starch
 Oil
Unknown Substances:
 A
 B
Procedure:
1. Make a small puddle (toonie sized) of distilled water on the watch glass
carefully.
2. Lay a small amount of the sample ionic or molecular substance on a
wooden splint then add it to the water.
3. Utilize the glass stirring rod to mix the substance with the water. After allow
it time to dissolve.
4. Make use of the conductivity tester to figure out if the water and
substance mixture conducts electricity. Record your observations.
5. Empty the mixture into the waste beaker when finished, rinse and dry; the
watch glass, conductivity tester and stir rod. Then clean up your area if
water spilled around with tissue paper.
Observations:
Substance
Name
Type of
Substance
Solubility in
Water
Salt (NaCl)
Ionic
Potassium
Chloride (KCl)
Copper (III)
Sulfate
(CuSO4)
Starch
Ionic
Did not
dissolve
Somewhat
dissolved
Somewhat
dissolved
Molecular
Fully Dissolved
Light off
Simple Sugar
(Glucose)
Oil
Molecular
Fully Dissolved
Molecular
Unknown A
-
Unknown B
-
Did not
dissolve
Somewhat
dissolved
Somewhat
dissolved
Light
on/flashing
Light off
Ionic
Observation
when testing
for
conductivity
Solid Light
Solid Light
Light off
Light off
Solid Light
Conductivity
Conducted
very well
Conducted
very well
Conducted
well
Did not
conduct
Conducted
well
Did not
conduct
Did not
conduct
Conducted
well
Analysis:
In my observation I realized that the ionic substances either conducted
electricity well or very well. Also molecular substances actually did the opposite,
and did not conduct electricity very well, either than simple sugar (glucose).
Sugar was the only molecular substance that had a flashing light on the tester. In
addition I noticed one of the unknown substances did conduct electricity and
one did not.
Sources of Error:
Unfortunately there were errors during the lab. People in the group forgot
to put on their safety goggles in most of the experiments. Possible explosions of
some sort or malfunctions could’ve occurred and there were possibilities of
injuries. Also in some experiments too much of either molecular or ionic
substance was placed on the watch glass with the water, which could’ve been
a major problem if that had a big effect on the results. In the future how these
flaws can be avoided is by, making sure you are secured and protected should
be your first priority, and also reading how much of the substance you place.
Discussion:
1.
When ionic substances are mixed in the water, electricity is given
off. Also these substances either partially mixed in the water, or did not
mix into the water. You could tell them apart when they were combined.
Therefore it either conducts well or very well and substances weren’t
completely mixed in water.
2.
When molecular substances are mixed in to the water mostly
electricity wasn’t conducted, except for glucose. Also when substance
was placed on the water it mixed very well together or partially dissolved,
except for oil. Therefore the majority of molecular substances mixed well
and did not give off electricity.
3.
Based on my answers in questions one and two I believe it is very
simple to tell apart which unknown substance is which compound. Since
ionic substances tend to give off electricity and either does not or partially
dissolve, I would predict the unknown substance closest to those two facts
is an ionic compound. Also the unknown substance that does not
conduct electricity and either mixes well or partially belong to the
molecular compound. This is how I would determine which substance
belongs to which compound.
4.
I strongly believe that potassium bromide is unknown substance B
and table sugar is unknown substance A. Potassium bromide is an ionic
compound since potassium (K) is on the metal side of the periodic table,
and bromide (Br) is on the non-metal side of the periodic table (above
staircase). Table sugar is a molecular compound since sugar as stated
before in the observation table is non-metal. This explains my answer
because as I stated before in question three, the ionic compound will
either partially dissolve or not dissolve, and conduct electricity. In my
observation substance B fell right into that analysis. On the other hand,
table salt is a molecular compound because it partially dissolved and did
not conduct electricity, which was the analysis for molecular compounds
according to the observations. Therefore potassium bromide, unknown
substance B, is an ionic compound, and table sugar, unknown substance
A, is a molecular compound.
Conclusion:
In conclusion I’ve acknowledged a lot of information during this experiment.
It was revealed that ionic compounds either partially mix into water or do not
mix at all. Also electricity is conducted with this compound. But molecular
compounds also either partially mix into water, but do mix completely too,
causing them not to conduct electricity. In addition a mystery was solved,
discovering that unknown substance A is a molecular compound (non-metal
and non-metal) and unknown substance B is an ionic compound (metal and
non-metal). Therefore there is a big difference between ionic and molecular
compounds and what they can/cannot do.
References:
 Ionic and Molecular compound package given by teacher
 Periodic table of elements