Lab Investigation
Comparing Ionic and Molecular Substances
Akshana Wettewa
9/30/2011
Comparing Ionic and Molecular Substances
By: Akshana Wettewa
Introduction: There are two kinds of ions; positive ions and negative ions. Positive ions are called
Cations. Negative ions are called Anions. When an atom becomes an ion it wants to go back to neutral
form so it makes bonds with other elements. One type of bond is an ionic bond. In ionic bonds it
involves a transfer of electrons from a non-metal atom to a metal atom. Another type of bond is a
covalent bond. A covalent bond is when a non-metal atom and another non-metal atom. An electrolyte
is a substance that dissolves in water to produce ions. To find out if the compound is an electrolyte I
tested it in water with a conductivity tester. If the LED light lights up then it is an electrolyte.
Purpose: The purpose of the experiment is to examine the solubility in water and conductivity of ionic
and molecular (covalent) bonds and also to find out what the unknown substances are.
Hypothesis: If water is added, then the ionic mixtures will conduct electricity, since ionic compounds are
made up of a metal atoms which is a good conductor of electricity. If water is added, then the molecular
compounds will not conduct electricity, since molecular compounds are made up of non-metal atoms
which are not good conductors of electricity. I think that the solubility for the ionic substances and
molecular substances will change for each substance.
Materials:
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Watch Glass
Stir Rod
Conductivity Tester
Sample Beaker
Wooden Splint
Distilled Water Bottle
Waste Beaker
Ionic Substances
 Salt (NaCl)
 Potassium Chloride (KCL)
 Copper (II) Sulfate (CuSO4)
Molecular Substances
 Simple Sugar (glucose)
 Starch
 Oil
Unknown Substances A and B
Procedure:
Step 1: Using the bottle of distilled water add enough water droplets to the watch glass.
Step 2: Take the wooden splint and place a small amount on to it, then drop it in the water.
Step 3: Working with the glass stirring rod mix the water and the substance together. Give it
some time to dissolve.
Step 4: Put the conductivity tester into the solution to assess whether or not it conducts
electricity. Record your observations.
Step 5: Clear the waste out of the watch glass and drop it into a waste beaker. Make sure to
rinse and dry the stir rod, watch glass and the conductivity tester before going to the next
station.
Independent Variable: Water
Dependant Variables: Ionic substances, Molecular Substances
The controlled variables are how much water and how much of the substances are put in.
Observations:
Table 1: Solubility and Conductivity of Ionic and Molecular Substances
Substance Name
Type of
Substance
(Ionic or
Molecular)
Solubility in
Water
(dissolved
well/partially
dissolved/did
not dissolve)
Observation
when testing for
Conductivity
(light off/ light
on steadily/light
flashing)
Conductivity
(did not
conduct/
conducted well/
conducted very
well)
Conducted very
well
Conducted very
well
Salt(NaCl)
Ionic
Dissolved well
Light on steadily
Potassium
Chloride (KCL)
Ionic
Partially
dissolved
Light on steadily
Copper (II)
Sulfate (CuSO4)
Ionic
Dissolved well
Light off
Did not conduct
Simple Sugar
(glucose)
Molecular
Dissolved well
Light off
Did not conduct
Starch
Molecular
Light on
Conducted well
Oil
Unknown A
Unknown B
Molecular
Molecular
Ionic
Partially
dissolved
Does not dissolve
Dissolved well
Dissolved well
Light off
Light off
Light on steadily
Did not conduct
Did not conduct
Conducted very
well
Analysis:
Results: The salt and water mixture dissolved well and the light had stayed on steadily. This
means that it conducted very well. Also when we put the conductivity tester into the salt and
water mixture there appeared yellow and white fizz. The potassium chloride and water mixture
partially dissolved and the light stayed on steadily. This means that the mixture conducted very
well. The copper sulfate and water mixture dissolved well but the light was off. This means that
it did not conduct electricity. The simple sugar (glucose) and water mixture dissolved well but
the light was off. This means that the mixture did not conduct electricity. The starch and water
mixture partially dissolved and the light was on but not very bright. This means that the mixture
conducted electricity. Oil and water mixture did not dissolve and the light was off. This means it
did not conduct electricity. The unknown A mixture dissolved well but the light was off. This
means the unknown mixture did not conduct electricity. The unknown B mixture dissolved well
and the light was on steadily. This means the unknown B mixture conducted very well.
Error Analysis: In the experiment I think that there were some faults throughout the
experiment. To be more accurate we should have measured the water and the amount of
substance before mixing them. We may not have waited long enough for some of the mixtures
to dissolve therefore changing our outcomes.
Discussion:
1. The ionic substances for the most part dissolved fairly well. Salt and copper sulfate
dissolved well and potassium chloride partially dissolved. As for the conductivity for the
ionic substances it was different. Salt conducted very well because of the presence of ions.
Also potassium chloride conducted very well. However, copper sulfate did not conduct any
electricity. According to my results most ionic compounds dissolve well and conduct
electricity. Of course there are exceptions as well in this case it was potassium chloride.
2. The molecular compounds had various stages of dissolving. Simple sugar (glucose) dissolved
well were as starch only partially dissolved and oil did not dissolve at all. The molecular
compounds for the most part did not conduct electricity. Simple sugar and oil did not
conduct electricity. This is because simple sugar is an organic mixture therefore it does not
conduct electricity. However starch conducted very well. According to my results most
molecular substances do not conduct electricity but there always will be exceptions in this
case it was starch.
3. I think that using these properties I could tell if the substance was molecular or ionic. If the
unknown mixture conducted electricity well and dissolved well I would guess that it was an
ionic compound. If the unknown mixture did not conduct electricity well I would guess that
it was a molecular compound.
4. I think that unknown B mixture is potassium bromide because it dissolved well and
conducted very well. Both of these properties are properties of ionic mixtures. Since
potassium bromide is an ionic substance it has to be unknown B mixture. I think that
unknown A mixture is table sugar (sucrose) because it dissolved well but did not conduct
electricity. This was similar to simple sugar (glucose) which also had the same results. Both
of these are properties of molecular substances. Since table sugar is a molecular compound
it has to be unknown A mixture.
Conclusion: In conclusion I found out that the electrolytes were salt, potassium chloride,
potassium bromide and starch. The non electrolytes were copper sulfate, simple sugar
(glucose), table sugar (sucrose) and oil. Most ionic compounds dissolve well and conduct
electricity. Most molecular substances do not conduct electricity. In my hypothesis I was correct
about ionic compounds being good conductors and molecular compounds being poor
conductors.
References
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McCurry John and Fay Robert C. Chemistry third edition. United States.
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"Electrolytes." Welcome to Waterloo Science | UW Faculty of Science. Web. 29 Sept. 2011.
<http://www.science.uwaterloo.ca/~cchieh/cact/c120/electrolyte.html>.