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J. W. Hill, R. H. Petrucci, T. W. McCreary, & S. S. Perry General Chemistry 4th edition

Problem 18.28

Use the half–reaction method to balance the following equations in acidic solution.

(a) Ag(s) + NO3(aq)Ag+(aq) + NO(g)

(b) H2O2(aq) + MnO4(aq)Mn2+(aq) + O2(g)

(c) Cl2(g) + I(aq)Cl(aq) + IO3(aq)







Answer:

(a) Ag(s) + NO3(aq)Ag+(aq) + NO(g)

Oxidation

Ag(s)Ag+(aq) + e

Reduction

NO3(aq)NO(g) + 2 H2O(l)

NO3(aq) + 4 H+(aq)NO(g) + 2 H2O(l)

NO3(aq) + 4 H+(aq) + 4 e NO(g) + 2 H2O(l)

Combine the half–reactions with equal numbers of electrons

[Ag(s)Ag+(aq) + e] × 3

NO3(aq) + 4 H+(aq) + 3 e NO(g) + 2 H2O(l)

Net reaction

3 Ag(s) + NO3(aq) + 4 H+(aq)3 Ag+(aq) + 2 H2O(l) + NO(g)



(b) H2O2(aq) + MnO4(aq) Mn2+(aq) + O2(g)

Oxidation

H2O2(aq)O2(g) + 2 H+(aq)

H2O2(aq)O2(g) + 2 H+(aq) + 2 e

Reduction

MnO4(aq)Mn2+(aq) + 4 H2O(l)

MnO4(aq)+ 8 H+(aq)Mn2+(aq) + 4 H2O(l)

MnO4(aq) + 8 H+(aq) + 5 e Mn2+(aq) + 4 H2O(l)

Combine the half–reactions with equal numbers of electrons

[H2O2(aq)O2(g) + 2 H+(aq) + 2 e] × 5

[MnO4(aq) + 8 H+(aq) + 5 e Mn2+(aq) + 4 H2O(l)] × 2

Net reaction, after eliminating species common to both sides

5 H2O2(aq) + 2 MnO4(aq) + 6 H+(aq)2 Mn2+(aq) + 8 H2O(l) + 5 O2(g)



(c) Cl2(g) + I(aq)Cl(aq) + IO3(aq)

Oxidation

I(aq) + 3 H2O(l)IO3(aq)

I(aq) + 3 H2O(l)IO3(aq) + 6 H+(aq)

I(aq) + 3 H2O(l)IO3(aq) + 6 H+(aq) + 6 e

Reduction

Cl2(g)2 Cl(aq)

Cl2(g) + 2 e2 Cl(aq)

Combine the half–reactions with equal numbers of electrons

I(aq) + 3 H2O(l)IO3(aq) + 6 H+(aq) + 6 e

[Cl2(g) + 2 e2 Cl(aq)] × 3

Net reaction

3 Cl2(g) + I(aq) + 3 H2O(l)6 Cl(aq) + IO3(aq) + 6 H+(aq)