Honors Chemistry

Answers to Chapter 18 Study Questions

 

1. a) -3; [x + 3(1) = 0] b) 0 c) +4; [x +2(-2) = 0] d) +5; [x + 3(-2) = -1]

2. a) Br2 b) I c) Br d) Br2 e) I-

3. First determine whether substances may be oxidized or reduced, then look up Eoox for reducing agents and Eored for oxidizing agents and list in order.

Oxidizing agents (are reduced): H+ (Eored = 0 V).

Reducing agents (are oxidized): Ni (Eoox = +0.23 V), Au (Eoox = -1.50 V), Mg (Eoox = +2.37 V).

Both: Sn2+ (Eored = -0.14 V; Eoox = -0.15 V), Fe2+ (Eored = -0.44 V, Eoox = -0.77 V), Cl2 (Eored = 1.36 V, Eoox = -1.47 V,).

Oxidizing agents (list in order of decreasing Eored): Cl2 > H+ > Sn2+ > Fe2+

Reducing agents (list in order of decreasing Eoox): Mg > Ni > Sn2+ > Fe2+ > Cl2 > Au

4. a) ox: [Ag Ag+ + e-] x 2; red: Cu2+ + 2 e- Cu

balanced: 2 Ag(s) + Cu2+(aq) 2 Ag+(aq) + Cu(s)

Eo = Eoox(Ag) + Eored(Cu2+) = -0.80 V + 0.34 V = -0.46 V. Not spontaneous.

b) ox: [Ni(s) Ni2+ + 2 e-] x 5; red: [5 e- + 8 H+ + MnO4- Mn2+ + 4 H2O] x 2

balanced: 5 Ni(s) + 16 H+(aq) + 2 MnO4-(aq) 5 Ni2+(aq) + 2 Mn2+(aq) + 8 H2O

Eo = Eoox(Ni) + Eored(MnO4-) = +0.23 V + 1.51 V = +1.74 V. Spontaneous.

c) ox: [2 H2O + Mn2+ MnO2 + 4 H+ + 2 e-] x 3

red: [3 e- + 4 H+ + NO3- NO + 2 H2O] x 2

balanced: 2 H2O + 3 Mn2+(aq) + 2 NO3-(aq) 3 MnO2(s) + 4 H+(aq) + 2 NO(g)

Eo = Eoox(Mn2+) + Eored(NO3-) = -1.21 V + 0.96 V = -0.25 V. Not spontaneous.

5. a) Eo = Eoox(Fe) + Eored(Fe3+) = +0.44 V + 0.77 V = +1.21 V. Spontaneous.

b) Eo = Eoox(I-) + Eored(Zn2+) = - 0.54 V - 0.76 V = -1.30 V. Not spontaneous.

6. Eoox(Br-) = -1.09 V. An ion will oxidize Br- if it has an Eored > +1.09 V.

a) Eored(Pb2+) = -0.13 V No. b) Eored(H+) = 0 No.

c) Eored(Au3+) = +1.50 V Yes. d) Eored(MnO4-) = +1.51 V Yes.

Answer: Au3+ and MnO4-

7. a) Eoox(Al) = +1.66 V; Eoox(Pb) = +0.13V. Al has a greater tendency to be oxidized. Thus, for spontaneous reaction, Al will be oxidized and Pb will be reduced:

2 Al(s) + 3 Pb2+(aq) 2 Al3+(aq) + 3 Pb(s)

 

 


b) c) lead (Pb); since Pb2+ Pb

 

 

 

 

 

 

 

 

 

 

 

8. a) Iron (Fe) is the strongest reducing agent because it is always oxidized. It reduces all of the other metals.

b) Gold (Au) is the weakest reducing agent because it is never oxidized.

c) Using the voltages of the other metals with Pb.

Half-reaction

Eored (volts)

Au3+ + 3 e- Au

+ 0.80 v

Pb2+ + 2 e- Pb

0.00 v

Ni2+ + 2 e- Ni

- 0.10 v

Fe2+ + 2 e- Fe

- 0.25 v