Science 10 – Lab #1
Name: _______________
Properties of Molecular & Ionic Compounds
Purpose: To determine which compounds in this investigation are composed of molecules and which are
composed of ions.
Introduction: The forces of attraction between particles in a compound affect the physical properties of
the compound. Weak forces of attraction hold together the atoms in a molecular compound, while strong
forces of attraction hold together oppositely charged ions in an ionic compound. Thus, molecular and
ionic compounds have different physical properties.
Materials & Apparatus:
 hot plate
 aluminium foil
 conductivity tester (light
bulb, wire and a battery)
 magnifying lens
 scoopula
 eye goggles
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tongs
four plastic trays, labelled
five small (50 ml) beaker
stirring rod
distilled water
four unknown substances
Procedure:
1.
Examine a small sample of each substance
using a magnifying lens. Record its appearance.
Note, in particular, if the edges of the sample have
a characteristic shape.
2. CAUTION: Use the proper “wafting” technique to carefully smell each
compound. If you detect an odour, try to describe it in your table.
3.
Test the hardness of each substance by rubbing a small sample
between your thumb and forefinger. Use words such as “soft”,
“waxy”, and “brittle” to record your observations. Wash your hands
in between each substance and after you are finished testing all substances.
CAUTION: Normally you would NOT touch chemicals with your bare hands! These substances
are everyday substances that are non-toxic. So, for this case, gloves are not needed.
4.
Add a small amount of distilled water to each of five beakers. Add a small amount of each
substance to four of the beakers. Stir with a stirring rod and note whether the substance dissolves
completely. Make sure that the stirring rod is cleaned between each use.
5.
Test each of these solutions for conductivity, using a
conductivity tester (You may have to wait for this device,
so be patient). If the light goes on completely, it conducts
electricity, if not, it doesn’t. Clean the tips of the conductivity
tester between samples. Test the conductivity of the fifth beaker distilled water alone. (This is your control).
Science 10 – Lab #1
Name: _______________
6.
CAUTION: Using a clean scoopula, place a small amount of each substance on a piece of
aluminium foil. Then place the foil on the hot plate. If the substance melts easily, record the
melting point as “low” If it does not melt, record the melting point as “high”. If the substance is
already a liquid, then obviously, it has a low melting point! Use tongs to remove the foil from the
hot plate. Clean the scoopula between samples.
7.
Clean up your workstation, and ensure that all supplies are put back where you found them. If
your group has completed all steps to the lab, you may start working on your analysis questions.
Analysis Questions:
1.
Which substances have edges with a characteristic shape? What does this suggest about the
arrangement of their particles?
2.
Which substances have no odour, or are hard or brittle? What do these properties suggest
about the strength of the forces of attraction?
3.
Classify the test substances as electrolytes and non-electrolytes.
4.
Which of the substances are made of ions and which are made of atoms covalently bonded
to each other? Check your results with other teams in the class. Discuss any conclusions
that you disagree on.
5.
Why was a control needed for step 5 above?
6.
Why is it important to use distilled water in step 5?
7.
Define the term “aqueous solution”.
8.
Why is important to use separate trays and to not use materials without cleaning them in
between samples?
9.
Examine the table from your textbook on page 154. Indicate whether you think that the
substances listed have ionic or covalent bonds.
10.
Predict which compound would have the lower melting point: Na2S or NO2. Explain.
11.
Predict which compound is more soluble in water: I2 or CuCl2. Explain.
Create a table like the following in your notebook to record your observations.
Substance Appearance Odour Hardness
Solubility Conductivity Relative
in H2O
in aqueous
melting point
solution
A
B
C
D
Ionic or
Covalent?
To be passed in: This lab sheet; Neatly completed data table (on a separate sheet of paper; Answers
to analysis questions – neatly written in full sentences.