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110 Chapter 7
10. Apply Faraday's Second Law again:

6H,O(aq) + 4Au3+(aq) + 4Auo,,) + 3O2(g) + 12H+(aq)
3 mol of 02(g) + 4 mol of Au; 1 mol of 02(g) + (4/3) mol of Au;
4 x 96500 C + (4/3) mol of Au (t); 1 C + (4/3)/(4 x 96500)
mol of Au = 3.45 x mol of Au; 2334.678 C -+ 0.00805464
mol = 1.59 g of Au.

Answer: 1.59 g

SUMMARY
This completes the section on electrochemistry. The following mul-
tiple-choice test and the six subsequent longer questions contain
questions on both galvanic and electrolytic cells.

MULTIPLE-CHOICE TEST
1. The oxidation state of boron in Na2BeB408.7H20 is:
(a) I (b) I1 (c) 111 (d) IV
2. For the reaction UA KMn04 + uB Fe(C103)3 +, the stoichio-
metry ratio vA:vB is:
(a) 6:5 (b) 5:6 (c) 7:6 (d) 6:7
3. What energy change occurs in an electrolytic cell?
(a) chemical to electrical; (b) electrical to chemical; (c) both
electrical to chemical and chemical to electrical; (d) you cannot
say for sure-such changes are concentration dependent.
4. For the electrochemical cell Zn I Zn2 + 11 Fe3 +, Fe2 + JPt, which of the
following statements is correct, given that
E"(Zn2+,Zn)= -1.18 VandE"(Fe3+,Fe2+) = +0.44V?
(a) Both electrodes are metal-metal-ion electrodes; (b) The
Zn/Zn2+ electrode is the cathode; (c) ELn = -0.74 V; (d)
Ekll = + 1.62 V.
5. When 1.48 A of current is passed through a solution of ZnS04
for 1.5 hours, the mass in g, of Zn deposited at the cathode is:
(a) 0.045 (b) 5.42 (c) 0.00075 (d) 2.71
Molar mass (M) of Zn = 65.39 g mol-' and I: = 96500 C
mol-'.
6. Determine AGO in kJ mol- ' at 25 "C for the following reaction:
Sn2 + (aq) + 2Fe3 + (aq) --+ Sn4+ (as) + 2Fe2 + (as)