Page 15 - Spotlight A+ Form 4 & 5 Chemistry KSSM

Form
4
Chapter 5 Chemical Bond Chemistry

4. The switch is turned off and the lead(II) 6. Steps 1 to 5 are repeated using naphthalene,
bromide, PbBr powder is then heated until it C H to replace lead(ll) bromide, PbBr .
2 10 8 2
melts completely. 7. The observation on the light bulb is recorded.
5. The switch is turned on again and the
observation is made on the light bulb.
Results:
Table 5.6
Observation
Compound Physical state Inference
on the light bulb
©PAN ASIA PUBLICATIONS
Lead(II) Solid The bulb does not light up. PbBr cannot conduct electricity in solid state
2
bromide, but can conduct electricity in molten state.
PbBr Molten The bulb lights up.
2
Naphthalene, Solid The bulb does not light up. C H cannot conduct electricity in solid and
10 8
C H molten states.
10 8
Molten The bulb does not light up.
Conclusion: Variables:
The hypothesis is accepted. Lead(II) bromide, (a) Manipulated: Type of compound, magnesium
PbBr is an ionic compound which able to conduct chloride, MgCl and naphthalene, C H
2 2 10 8
–
2+
electricity in molten state but not in solid state. (b) Responding: Solubility of Mg ions and Cl
Naphthalene, C H is a covalent compound that ions
10 8
cannot conduct electricity both in solid and molten (c) Fixed: Quantity of compound, volume of
states. solvent, temperature
Discussion: Procedure:
1. Lead(II) bromide, PbBr consists of lead(II) ions,
2
Pb and bromide ions, Br . In solid state, the
2+
–
oppositely-charged ions are held together by Magnesium
strong electrostatic forces of attraction in the Distilled chloride, Cyclohexane, C H 12
6
lattice structure. They are in fixed positions and water MgCl
CHAP. cannot move freely. As a result, solid lead(II) 2 CHAP.
5 bromide, PbBr cannot conduct electricity. Figure 5.37 5
2
2. When lead(II) bromide, PbBr is heated until 1. Half spatula of magnesium chloride, MgCl
2 2
it melts to become a liquid, the lead(II) crystals is placed in two test tubes separately.
ions, Pb and bromide ions, Br are free to 2. 5 cm of distilled water is added to the first
2+
–
3
move. Therefore, molten PbBr can conduct test tube and shaken.
2
electricity. 3. 5 cm of cyclohexane, C H is added to the
3
12
6
3. Naphthalene, C H only consists of neutral second test tube and shaken.
10 8
molecules. It does not contain ions. Thus, it 4. The solubility of magnesium chloride, MgCl in
cannot conduct electricity either in solid state both solvents are observed and recorded. 2
or molten state. 5. Steps 1 to 4 are repeated using solid
naphthalene, C H to replace magnesium
10 8
chloride, MgCl .
2
Ionic compounds which are soluble in water also Results:
can dissociate in water to produce free moving Table 5.7
ions.
Compound Solubility Solubility in
in water cyclohexane
B Solubility
Hypothesis: Magnesium Soluble Insoluble
chloride, MgCl
Most ionic compounds are soluble in water but 2
insoluble in organic solvents while most covalent
compounds are insoluble in water but can dissolve Naphthalene Insoluble Soluble
in organic solvents. C H 8
10
5.7.1 133