X. Electrochemistry
Electrochemistry practice problems
There are a total of 15 electrochemistry practice problems, which are important content-oriented in the summary part of this chapter. Click the ‘Answer’ button to see the corresponding answers and explanations, and click the ‘Go back’ button to slove the next questions.
4. Which of the following is an INCORRECT statement for the reaction?
Zn(s)|Zn2+(aq)||Cu2+(aq)|Cu(s) Total Eo = +1.1V
A. There is a salt bridge.
B. The reaction at anode is Zn(s) → Zn2+(aq) + 2e–.
C. The reduction reaction is Cu2+(aq) + 2e– → Cu(s).
D. Electro flow is from Cu(s) to Zn(s)
E. This is a galvanic cell.
7. Which of the following is an INCORRECT statement about electrochemical cells?
A. Voltaic and Daniell cells are ΔG < 0.
B. Daniell cells have a salt bridge to keep electrical neutral solution.
C. Electrolytic cells generate an electric current by an external power source.
D. Polarizing action happens in voltaic cells.
E. None of these answers are incorrect. All are correct.
10. The standard free-energy change, ΔG, is – 579kJ when the value of Eo is 2V. How many electrons are transferred?
A. 2
B. 3
C. 4
D. 5
E. 6
12. A constant current of 2.5A is passed through the solution of AgNO3 for 2 minutes. How much charge is produced?
A. 1.25
B. 5
C. 50
D. 150
E. 300
13. A constant current of A is used in an aqueous solution of PbSO4 for 2 hours 40 minutes 50 seconds. When the value of Faraday is 0.01F, how much of the current A is used?
A. 0.01A
B. 0.02A
C. 0.1A
D. 0.2A
E. 1.0 A
14. When 3F of Mg is used for the reaction, how many moles of Mg are needed?
Mg2+(aq) + 2e– → Mg(s)
A. 0.7
B. 1.5
C. 2.0
D. 3.o
E. 6.0
15. How many volumes of H2 are produced when the aqueous solution of NaBr is electrolyzed in a container for 1 hour 20 minutes 25 seconds with a constant current of 2A at STP?
2H2O(l) + 2Br–(aq) → Br2(l) + H2(g) + 2OH–(aq)
A. 2.2L
B. 4.4L
C. 8.8L
D. 17.6L
E. 35.2L
Answers
2. A
From the oxidation reaction, Na(s) → Na+(aq) + 2e–, the strongest reducing agent is Na(s).
3. D
The positive total value of Eo from the reaction indicates a spontaneous reaction. All are spontaneous reactions except D.
Reduction half-reaction |  |
Oxidation and reduction |  |
 |  |
4. D
“||” means the salt bridge. Electro flow is from Zn(s) (anode) to Cu(s) (cathode). Because total Eo is positive, this reaction is by the galvanic cell (spontaneous reaction
5. C
Shorthand notation |  |
Oxidation and reduction |  |
Multiply coefficient to cancel electrons |  |
 |  |
The total Eo = 0.56V
0.56V = –x V+ 1.36 V
x = +0.8 V
7. E
Voltaic cells occurs polarizing action, which hinder the accepting electrons by sticking H2 (2e– + 2H+) at cathode. So, the electric current is decreased as time goes by. To prevent this action, Daniell cells have a salt bridge to make electrical solution neutral.
