ANSWERS TO END-OF-CHAPTER QUESTIONS

Answer:
a. The electrolyte completes the electrical circuit. It provides a medium for transport of ions,
thus allowing charge to be transferred.
b. KOH paste
c. H2SO4(aq)
12. These are the incomplete equations for the half-reactions in a lead storage battery. They do
not show the electrons either lost or gained.
Pb(s) + SO4 2– (aq) ⎯→ PbSO4(s)
PbO2(s) + 4 H + (aq) + SO4 2– (aq) ⎯→ PbSO4(s) + 2 H2O(l)
a. Balance both equations with respect to charge by adding electrons on either side of the
equations, as needed.
b. Which half-reaction represents oxidation and which represents reduction?
c. One of the electrodes is made of lead, the other of lead dioxide. Which is the anode and
which is the cathode?
Answer:
a. Pb(s) + SO4 2– (aq) ⎯→ PbSO4(s) + 2 e –
PbO2(s) + 4 H + (aq) + SO4 2– (aq) + 2 e – ⎯→ PbSO4(s) + 2 H2O(l)
b. The first half-reaction shows electrons being lost, so it is the half-reaction of oxidation.
The second half-reaction shows electrons being gained, so it is the half-reaction of reduction.
c. Lead is being oxidized, so lead is the anode. Lead dioxide is being reduced, so it is the
cathode.
13. What is meant by the term hybrid car?
Answer:
In current usage, the term hybrid car refers to the combination of a gasoline engine with a
nickel-metal hydride battery, an electric motor, and an electric generator. Other hybrids using
fuel cells are either available or under development.
14. a. What is the role of the electrolyte in a fuel cell?
b. List two advantages fuel cells have over internal combustion engines.
Answer:
a. The electrolyte allows ions to move between the electrodes, thus completing the circuit.
b. Fuel cells using hydrogen gas (H2) as the fuel produce only water as a product, whereas
internal combustion engines produce many products including the greenhouse gas carbon
dioxide and pollutants such as carbon monoxide, soot, VOCs, and nitrogen monoxide. When
a fuel is oxidized in a fuel cell, 45–55% of the energy released is transferred into electricity.
Combustion engines are only 20–30% efficient because combustion releases energy in the
form of heat, which then must be transferred to electrical and/or mechanical energy.
15. Is the conversion of O2(g) to H2O(l) in a fuel cell an example of oxidation or reduction? Use
electron loss or gain to support your answer.
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