COVALENT AND IONIC COMPOUNDS
Purpose: To study the physical properties of covalent and ionic compounds.
Materials:
2 watch glasses
scoopula
crucible cover
clay triangle
ring clamp
test tube rack
retort stand
burner
flint lighter
test tube
stopper
cyclohexane
heat resistant pad
electrical conductivity
apparatus
sodium chloride (NaCl)
napthalene (C10H8)
Method:
1) Obtain a half-spoon of sodium chloride on one watch glass and a half-spoon of
napthalene on the other watch glass.
2) For each solid, note whether it has a distinctive odour i.e. is volatile.
3) Rub a small sample of each solid between your fingers. Note the relative hardness
of the two solids.
4) Place a few crystals of sodium chloride and napthalene side by side on
an aluminum dish. Place the dish on a hot place. Gently heat the substances until
one of the melts. Note which substance melts.
5) Add cyclohexane (a nonpolar solvent) to a clean dry test tube to a height of about
3 cm. Then add a few crystals of sodium chloride to the test tube. Stopper the test
tube and shake. Note whether the crystals were soluble or not. Dispose of the
mixture in the inorganic waste container. Then wash out the test tube.
6) Repeat step 5, this time using napthalene. Dispose of the mixture in the organic
waste container. Then wash out the test tube.
7) Add water (a polar solvent) to a clean dry test tube to a height of about 3 cm. Then
add a few crystals of sodium chloride to the test tube. Stopper the test tube and
shake. Note whether the crystals were soluble or not. Then wash out the test tube.
8) Repeat step 7, this time using napthalene. Dispose of the mixture in the organic
waste container. Then wash out the test tube.
9) Test the electrical conductivity of a mixture of napthalene and water. Note both the
degree of brightness of the light bulb and the degree of electrolysis around the
electrodes.
10) Repeat step 9, this time using a mixture of sodium chloride and water.
11) Dispose of any left over napthalene in the organic waste container. Dispose of any
left over sodium chloride in the inorganic waste container.
12) Clean up your work area and wash your hands.
Observations: Record your observations in an observations table of your own design.
Conclusions: Answer the following questions using full sentences.
1) Which substance was covalently bonded and which was ionic? How did you know?
2) a) If a solid has a distinctive odour, i.e. is volatile, the ions/molecules of the solid
must be able to easily leave its surface. Keeping that in mind, are the
molecules in covalent compounds or the ions in ionic compounds held together
by the strongest forces of attraction?
b) On the basis of your answer to 1) a), explain the results of the hardness and
fusibility tests.
3) Read pages 293-294 in your text. Explain the results of all of the solubility tests.
4) Read pages 78-79, 82 in your text. Explain the results of both electrical conductivity
tests.
Question:
A chemist was investigating a white solid which he knew was either calcium bromide
(CaBr2) or 1,4 – dichlorobenzene (C6H4Cl2). He tested the solid and found that it had a
distinctive odour, was soft, melted easily and was soluble in cyclohexane but not water.
What must have been the identity of the solid? Explain your answer.