Page 229 - Theory and Problems of BEGINNING CHEMISTRY

218 OXIDATION AND REDUCTION [CHAP. 14

(c) 4 H + Pb + PbO 2 + 2SO 4 2− −→ 2 PbSO 4 + 2H 2 O
+
−
(d) I 3 + 2Co(CN) 6 4− −→ 2Co(CN) 6 3− + 3I −
(e) V 2+ + H 3 AsO 4 −→ HAsO 2 + VO 2+ + H 2 O
−
( f ) Hg 2+ + 2CN −→ C 2 N 2 + 2Hg
2
(g) 2 VO 2+ + AsO 4 3− −→ AsO 2 + 2VO 2 +
−
14.38. The oxidizing ability of H 2 SO 4 depends on its concentration. Which element is reduced by reaction of Zn on H 2 SO 4
in each of the following reactions?
Zn + H 2 SO 4 (dilute) −→ ZnSO 4 + H 2
4Zn + 5H 2 SO 4 (conc) −→ H 2 S + 4H 2 O + 4 ZnSO 4
Ans. In the first reaction, hydrogen is reduced. In the second reaction, sulfur is reduced.

14.39. Complete and balance the following equation:
Sb 2 S 3 + HNO 3 −→ H 3 SbO 4 + SO 2 + NO
Ans. 3Sb 2 S 3 + 22 HNO 3 −→ 6H 3 SbO 4 + 9SO 2 + 22 NO + 2H 2 O

14.40. What is the maximum oxidation state of fluorine in any compound?
Ans. The only oxidation state of fluorine in a compound is −1; it is the most electronegative element. (It always
has control of both shared electrons, except in the element F 2 .)

14.41. Calculate the oxidation number of carbon in (a)CH 2 O and (b)CH 2 F 2 .
Ans. (a)0 (b)0

−
14.42. What is the more likely formula for bismuth in the +5 oxidation state—Bi 5+ or BiO 3 ?
Ans. BiO 3 . There are no 5+ monatomic ions.
−
14.43. Explain why direct current (dc) rather than alternating current (ac) is used for electrolysis. Why is direct current used
in cars?

Ans. In direct current, the electrons flow in the same direction all the time. In alternating current, the electrons flow
one way for a short period of time (typically 1 s), and then they flow the other way. To get any electrolysis
60
that is not immediately undone, direct current is required. Direct current is also used in cars because cells
generate direct current.