SCH 4C
Unit 1: Matter
Qualitative Chemistry
Name: ___________________________
Date: ___________________________
Lab: Classifying Solids Using Qualitative Physical Properties
Introduction:
Recall that molecules are made of only non-metals that share valence electrons. This sharing of electrons is called
a covalent bond. Ionic compounds are held together by ionic bonds. These bonds are formed between positively
and negatively charged ions. Ionic compounds may be made up of the ions of a metal and a non-metal, a metal
and a polyatomic ion or two polyatomic ions.
Because they are held together differently, molecules and ionic compounds have different qualitative physical
properties. Here is a table showing some of these differences.
Conductivity
Solubility in Water
Hardness
Melting point
(Does the substance conduct
(Will the substance
of the solid
of the solid
electricity?)
dissolve in water?)
Ionic compounds will conduct
Most ionic compounds Ionic solids are hard
High – often 500oC or
Ionic
are at least a little bit
and often brittle.
higher.
compound electricity when they are
molecule
dissolved in water (this makes
them electrolytes) or are molten.
Their ions cannot move in the
solid state, though, so they
cannot conduct electricity as
solids.
Acids are the only molecules that
will conduct electricity when
dissolved in water. This means
that the majority of molecules do
not conduct electricity.
soluble in water.
Some molecules are
soluble in water, but
there are a great many
that are not.
Different molecular
solids have different
amounts of hardness.
Some are soft and
some are really hard.
The melting points of
molecular solids are
usually quite a bit less
than for ionic
compounds.
Question
How do ionic solids and molecular solids compare on the basis of conductivity, solubility in water, hardness and
conductivity?
Hypothesis:
If ionic solids and molecular solids have different qualitative physical properties then ________________________
_____________________________________________________________________________________________ .
Materials
Goggles
4 small beakers
Distilled water
Sucrose
Conductivity meter
Potassium iodide
Camphor
Sodium chloride
Stir stick
Beaker for waste
Method
Part 1: Testing for Water Solubility
1.
2.
3.
4.
5.
6.
7.
Gather enough small beakers so that there can be one different solid in each one.
Use tape and a pencil to label the small beakers with the identity of one of the solids.
Pour 10 mL of distilled water into each beaker.
Add a small amount (just enough to fill up the end of a wooden splint) of each solid to its labelled beaker.
Use a stirring rod to gently mix the contents of each beaker. Wipe the stirring rod with a piece of paper
towel between beakers so you do not contaminate samples.
Record whether or not each solid has dissolved in water in your observation table.
You need the beakers and their contents for the next part of the activity so do not discard anything.
Part 2: Testing for Conductivity
1.
2.
Test each sample for electrical conductivity in the manner demonstrated by your teacher. Be sure to clean
off the conductivity meter in distilled water before moving between beaker samples.
Discard each solution by pouring it into the waste beaker provided.
Part 3: Testing for Hardness
1.
2.
3.
4.
5.
Use a wooden splint or a plastic spoon to place a few small crystals of one of the solids on a watch glass.
Try to crush the crystals between the wooden splint and the watch glass. Record your results.
Discard the crystals in the waste beaker.
Repeat the above procedure for each of the other solids.
Rank the solids from the one that was easiest to crush (call it #1) to the one that was hardest to crush (call
it #4) in your observation table.
Part 4: Melting Point
Write the following melting points into your observation table.
Potassium iodide, 686oC.; Sodium chloride, 801oC; camphor 177oC and sucrose 186oC.
Part 5: Classifying an Unidentified Sample
1.
Your teacher will provide you with an unknown sample. S/he will tell you the melting point. You need to
test for the other qualitative physical properties of the substance and record them in your table.
Observations:
Property
Solubility in Water
Substance
Potassium iodide
Conductivity When in
Water
Hardness of the Solid
Melting
Temperature of
the Solid
Sodium chloride
Camphor
Sucrose
(table sugar)
Unknown
Substance
Analysis:
Put the underlined title “Lab: Classifying Solids Using Qualitative Physical Properties” at the top of a piece of
looseleaf. Put the title “Analysis” underneath that title. Answer each of the following questions in full and
complete sentences.
1.
2.
3.
4.
Identify whether each one of the four solids tested in parts 1 – 4 of the procedure is an ionic solid or a
molecule. Use full sentences to explain your reasoning for EACH ONE. The table in the “Introduction”
part of the lab will help you.
Is the unknown substance a molecule or is it an ionic compound? Explain the reasoning for your choice.
Although you do not have a record of the qualitative physical properties of the following substances,
decide if each one is an ionic solid or a molecule based on its formula. [The first paragraph of the
“Introduction” should help you to remember how to do this.]
a) CH4
b) Li2SO4
c) NH4NO3
d) BaCl2
e) C2H3OH
Here are the ways we represent the bonding in molecules and in ionic compounds.
i)
Molecules
ii)
Ionic compounds
Use this information to draw out the identity of the ? for each of the following. [HINT: Use your answers
from #3 above to help determine which substance is a molecule and which is an ionic compound before
you do the drawings.]
Conclusion:
Write the underlined title “Conclusion” after your answers to the Analysis section. Write a few statements relating
your hypothesis to what you found out in the lab.