10.1 Balancing oxidation-reduction reactions  (Page 6/12)

If a 2.5 A current is run through a circuit for 35 minutes, how many coulombs of charge moved through the circuit?

For the scenario in the previous question, how many electrons moved through the circuit?

For each of the following balanced half-reactions, determine whether an oxidation or reduction is occurring.

(a) ${\text{Fe}}^{\mathrm{3+}}+{\text{3e}}^{\text{−}}⟶\text{Fe}$

(b) $\text{Cr}⟶{\text{Cr}}^{\mathrm{3+}}+{\text{3e}}^{\text{−}}$

(c) ${\text{MnO}}_4{}^{\mathrm{2-}}⟶{\text{MnO}}_4{}^{-}+{\text{e}}^{\text{−}}$

(d) ${\text{Li}}^{\text{+}}+{\text{e}}^{\text{−}}⟶\text{Li}$

For each of the following unbalanced half-reactions, determine whether an oxidation or reduction is occurring.

(a) ${\text{Cl}}^{\text{−}}⟶{\text{Cl}}_2$

(b) ${\text{Mn}}^{\mathrm{2+}}⟶{\text{MnO}}_2$

(c) ${\text{H}}_2⟶{\text{H}}^{\text{+}}$

(d) ${\text{NO}}_3{}^{-}⟶\text{NO}$

Given the following pairs of balanced half-reactions, determine the balanced reaction for each pair of half-reactions in an acidic solution.

(a) $\text{Ca}⟶{\text{Ca}}^{\mathrm{2+}}+{\text{2e}}^{\text{−}},$ ${\text{F}}_2+{\text{2e}}^{\text{−}}⟶{\text{2F}}^{\text{−}}$

(b) $\text{Li}⟶{\text{Li}}^{\text{+}}+{\text{e}}^{\text{−}},$ ${\text{Cl}}_2+{\text{2e}}^{\text{−}}⟶{\text{2Cl}}^{\text{−}}$

(c) $\text{Fe}⟶{\text{Fe}}^{\mathrm{3+}}+{\text{3e}}^{\text{−}},$ ${\text{Br}}_2+{\text{2e}}^{-}⟶{\text{2Br}}^{-}$

(d) $\text{Ag}⟶{\text{Ag}}^{\text{+}}+{\text{e}}^{\text{−}},$ ${\text{MnO}}_4{}^{-}+{\text{4H}}^{\text{+}}+{\text{3e}}^{\text{−}}⟶{\text{MnO}}_2+{\text{2H}}_2\text{O}$

Balance the following in acidic solution:

(a) ${\text{H}}_2{\text{O}}_2+{\text{Sn}}^{\mathrm{2+}}⟶{\text{H}}_2\text{O}+{\text{Sn}}^{\mathrm{4+}}$

(b) ${\text{PbO}}_2+\text{Hg}⟶{\text{Hg}}_2{}^{\mathrm{2+}}+{\text{Pb}}^{\mathrm{2+}}$

(c) $\text{Al}+{\text{Cr}}_2{\text{O}}_7{}^{\mathrm{2-}}⟶{\text{Al}}^{\mathrm{3+}}+{\text{Cr}}^{\mathrm{3+}}$

Identify the species that undergoes oxidation, the species that undergoes reduction, the oxidizing agent, and the reducing agent in each of the reactions of the previous problem.

Balance the following in basic solution:

(a) ${\text{SO}}_3{}^{\mathrm{2-}}(aq)+{\text{Cu(OH)}}_2(s)⟶{\text{SO}}_4{}^{\mathrm{2-}}(aq)+\text{Cu(OH)}(s)$

(b) ${\text{O}}_2(g)+{\text{Mn(OH)}}_2(s)⟶{\text{MnO}}_2(s)$

(c) ${\text{NO}}_3{}^{\text{−}}(aq)+{\text{H}}_2(g)⟶\text{NO}(g)$

(d) $\text{Al}(s)+{\text{CrO}}_4{}^{\mathrm{2-}}(aq)⟶{\text{Al(OH)}}_3(s)+{\text{Cr(OH)}}_4{}^{\text{−}}(aq)$

Identify the species that was oxidized, the species that was reduced, the oxidizing agent, and the reducing agent in each of the reactions of the previous problem.

Why is it not possible for hydroxide ion (OH ⁻ ) to appear in either of the half-reactions or the overall equation when balancing oxidation-reduction reactions in acidic solution?

Why is it not possible for hydrogen ion (H ⁺ ) to appear in either of the half-reactions or the overall equation when balancing oxidation-reduction reactions in basic solution?

Why must the charge balance in oxidation-reduction reactions?