Practice Quiz Chapter 21

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1.	A concentration cell is based on the aqueous reaction Cu²⁺(1.00 M) → Cu²⁺(0.0100 M) Calculate the potential of this cell if it operates at 25.0°C. Answer:

Electrolytic cells utilize electrical energy to drive non-spontaneous redox reactions.

True

False

A concentration cell consists of two Zn/Zn²⁺ electrodes. The electrolyte in compartment A is 0.10 M Zn(NO₃)₂and in compartment B is 0.60 M Zn(NO₃)₂. What is the voltage of the cell at 25°C?

0.010 V

0.020 V

0.023 V

0.046 V

E.	none of the above

A secondary cell (battery) can operate either as a galvanic or an electrolytic cell.

True

False

Two cells are connected in series, so that the same current flows through two electrodes where the following half-reactions occur
Cu²⁺(aq) + 2e^- → Cu(s) and Ag⁺(aq) + e^- → Ag(s)
For every 1.00 g of copper produced in the first process, how many grams of silver will be produced in the second one?

0.294 g

0.588 g

0.850 g

1.70 g

3.40 g

Which, if any, of the following metals would be capable of acting as a sacrificial anode when used with iron pipe? E°_Fe = -0.44 V; all E° values refer to the M²⁺/M half-cell reactions.

A.	copper, Cu, E° = 0.15 V

B.	cobalt, Co, E° = -0.28 V

C.	chromium, Cr, E° = -0.74 V

D.	tin, Sn, E° = -0.14 V

E.	None of these metals would be capable of acting as a sacrificial anode with iron.

Calculate E°_cell for the reaction of nickel(II) ions with cadmium metal at 25°C. K = 1.17 × 10⁵
Ni²⁺(aq) + Cd(s) → Cd²⁺(aq) + Ni(s)

0.075 V

0.10 V

0.12 V

0.15 V

0.30 V

In the electrolyte of an electrochemical cell, current is carried by anions moving toward the anode and cations moving in the opposite direction.

True

False

Consider the following balanced redox reaction
3CuO(s) + 2NH₃(aq) → N₂(g) + 3H₂O(l) + 3Cu(s)
Which of the following statements is true?

A.	CuO(s) is the oxidizing agent and copper is reduced.

B.	CuO(s) is the oxidizing agent and copper is oxidized.

C.	CuO(s) is the reducing agent and copper is oxidized.

D.	CuO(s) is the reducing agent and copper is reduced.

E.	CuO(s) is the oxidizing agent and N₂(g) is the reducing agent.

10.

In one or two short sentences each, explain what is meant by the following terms.
a. galvanic or voltaic cell
b. electrolytic cell
c. salt bridge
d. secondary battery or cell
e. primary battery or cell
f. glass electrode

Answer:

11.

What product forms at the anode during the electrolysis of molten NaBr?

Na⁺(l)

Na(l)

Br^-(l)

Br₃^-(l)

Br₂(g)

12.

Explain what is meant by a fuel cell. Provide a balanced equation to represent the reaction in any fuel cell of your choice.

Answer:

13.

Which one of the following statements about electrochemical cells is correct?

A.	In a salt bridge, current is carried by cations moving toward the anode, and anions toward the cathode.

B.	In the external wire, electrons travel from cathode to anode.

C.	The anode of a voltaic cell is labeled minus (-).

D.	Oxidation occurs at the cathode, in an electrolytic cell.

E.	None of the above statements is correct.

14.

Consider the reaction of iodine with manganese dioxide
3I₂(s) + 2MnO₂(s) + 8OH^-(aq) ↔ 6I^-(aq) + 2MnO₄-(aq) + 4H₂O(l)
The equilibrium constant for the overall reaction is 8.30 × 10^-7. Calculate ΔG°for the reaction at 25°C.

-15.1 kJ

-34.7 kJ

15.1 kJ

34.7 kJ

E.	none of the above

15.

Oxidation occurs at the cathode of a galvanic cell, but at the anode of an electrolytic cell.

True

False

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