Chapter 12
Understanding Concepts
1. For each reaction described below:
a) write a balanced chemical equation by inspection
b) write the ionic and net ionic equations
c) identify the oxidizing agent and the reducing agent
d) write the two half-reactions
i) zinc metal with aqueous silver nitrate
ii) aqueous cobalt(II) bromide with aluminium metal
iii) metallic cadmium with aqueous tin(II) chloride
2. When a metallic element reacts with a non-metallic
element, which reactant is
a) oxidized?
c) the oxidizing agent?
b) reduced?
d) the reducing agent?
3. Determine the oxidation number of each element
present in the following substances:
f) S8(s)
a) BaCl2(s)
b) Al4C3(s)
g) AsO33−(s)
c) KCN(s)
h) VO2+(s)
d) LiNO2(s)
i) XeO3F−(s)
e) (NH4)2C2O4(s) j) S4O63−(s)
4. Explain why the historical use of the word reduction,
that is, the production of a metal from its ore, is
consistent with the modern definitions of reduction.
5. Determine which of the following balanced chemical
equations represent redox reactions. For each redox
reaction, identify the oxidizing agent and the
reducing agent:
a) 2C6H6() + 15O2(g) → 12CO2(g) + 6H2O()
b) CaO(s) + SO2(g) → CaSO3(aq)
c) H2(g) + I2(s) → 2HI(aq)
d) KMnO4(aq) + 5CuCl(s) + 8HCl →
KCl(aq) + MnCl2(aq) + 5CuCl2(s) + 4H2O()
e) 2Ag+(aq) + Cu(s) → 2Ag(s) + Cu2+(aq)
f) Pb2+(aq) + S2−(aq) → PbS(s)
g) 2Mn2+(aq) + 5BiO3−(aq) + 14H+(aq) →
2MnO4−(aq) + 5Bi3+(aq) + 7H2O()
6. a) Examples of molecules and ions composed only of
vanadium and oxygen are listed below. In this list,
identify molecules and ions in which the oxidation
number of vanadium is the same:
V2O5(s)
VO(s)
VO3−(s)
+
V2O3(s)
VO2 (s)
VO43−(s)
2+
VO2(s)
VO (s)
V3O93+(s)
b) Is the following reaction a redox reaction?
2NH4VO3(aq) → V2O5(s) + 2NH3(g) + H2O()
474 MHR • Unit 6 Electrochemical Changes
Applying Concepts
7. Identify a polyatomic ion in which chlorine has an
oxidation number of +3.
8. If possible, give an example of each of the following:
a) a formation reaction that is a redox reaction
b) a formation reaction that is not a redox reaction
c) a decomposition reaction that is a redox reaction
d) a decomposition reaction that is not a redox reaction
e) a double-replacement reaction that is a redox reaction
f) a double-replacement reaction that is not a redox
reaction
9. Phosphorus, P4(s), reacts with hot water to form
phosphine, PH3(g), and phosphoric acid, H3PO4(aq).
a) Write a balanced chemical equation for this reaction.
b) Is the phosphorus oxidized or reduced? Explain
your answer.
10. The thermite reaction, which is highly exothermic,
can be used to weld metals. In the thermite reaction,
aluminium reacts with iron(III) oxide to form iron
and aluminium oxide. The temperature becomes so
high that the iron is formed as a liquid.
a) Write a balanced chemical equation for the reaction.
b) Is the reaction a redox reaction? If so, identify the
oxidizing agent and the reducing agent.
11. Describe a laboratory investigation that you could
perform to decide whether tin or nickel is the better
reducing agent. Include in your description all the
materials and equipment you would need, and
describe the procedure you would follow.
12. The following table shows the average formation, by
volume, of the air we inhale and exhale as part of a
biochemical process called respiration. (The values are
rounded.) How do the data indicate that at least one
redox reaction is involved in respiration?
Gas
oxygen
carbon dioxide
nitrogen and other gases
Inhaled Air
Exhaled Air
(% by volume) (% by volume)
21
0.04
79
16
4
80
13. Explain why you would not expect sulfide ions to act as
an oxidizing agent.