Question 17.5: Consider the voltaic cell in which the reaction is 2Ag^+(aq)...
Consider the voltaic cell in which the reaction is
2Ag^+(aq) + Cd(s) \longrightarrow 2Ag(s) + Cd^{2+}(aq)
a Use Table 17.1 to calculate E° for the voltaic cell.
STRATEGY
1. Assign oxidation numbers to each element so you can decide which element is reduced and which one is oxidized.
2. Write the oxidation and reduction half-reactions together with the corresponding E^{\circ}_{ox} and E^{\circ}_{red}.
Recall that E^{\circ}_{ox}= -(E^{\circ}_{red}).
3. Add both half-reactions (make sure you cancel electrons) and take the sum of E^{\circ}_{ox} and E^{\circ}_{red} to obtain E° for the cell.
b If the value zero is arbitrarily assigned to the standard voltage for the reduction of Ag^+ ions to Ag, what is E^{\circ}_{red} for the reduction of Cd^{2+} ions to Cd?
Table 17.1 Standard Potentials in Water Solution at 25°C | ||||
Acidic Solution, [H^+] = 1 M | ||||
{E^{\circ}}_{red} (V) | ||||
Li^+(aq) + e^- | \longrightarrow Li(s)\blacktriangleleft ⓘ | -3.04 | ||
K^+(aq) + e^- | \longrightarrow K(s) | -2.936 | ||
Ba^{2+}(aq) + 2e^{-} | \longrightarrow Ba(s) | -2.906 | ||
Ca^{2+}(aq) + 2e^- | \longrightarrow Ca(s) | -2.869 | ||
Na^+(aq) + e^- | \longrightarrow Na(s) | -2.714 | ||
Mg^{2+}(aq) + 2e^- | \longrightarrow Mg(s) | -2.357 | ||
Al^{3+}(aq) + 3e^- | \longrightarrow Al(s) | -1.68 | ||
Mn^{2+}(aq) + 2e^- | \longrightarrow Mn(s) | -1.182 | ||
Zn^{2+}(aq) + 2e^- | \longrightarrow Zn(s) | -0.762 | ||
Cr^{3+}(aq) + 3e^- | \longrightarrow Cr(s) | -0.744 | ||
Fe^{2+}(aq) + 2e^- | \longrightarrow Fe(s) | -0.409 | ||
Cr^{3+}(aq) + e^- | \longrightarrow Cr^{2+}(aq) | -0.408 | ||
Cd^{2+}(aq) + 2e^- | \longrightarrow Cd(s) | -0.402 | ||
PbSO_4(s) + 2e^- | \longrightarrow Pb(s) + {SO_4}^{2-}(aq) | -0.356 | ||
Tl^+(aq) + e^- | \longrightarrow Tl(s) | -0.336 | ||
Co^{2+}(aq) + 2e^- | \longrightarrow Co(s) | -0.282 | ||
Ni^{2+}(aq) + 2e^- | \longrightarrow Ni(s) | -0.236 | ||
AgI(s) + e^- | \longrightarrow Ag(s) + I^-(aq) | -0.152 | ||
Sn^{2+}(aq) + 2e^- | \longrightarrow Sn(s) | -0.141 | ||
Pb^{2+}(aq) + 2e^- | \longrightarrow Pb(s) | -0.127 | ||
2H^+(aq) + 2e^- | \longrightarrow H_2(g) | 0 | ||
AgBr(s) + e^- | \longrightarrow Ag(s) + Br^-(aq) | 0.073 | ||
S(s) + 2H^+(aq) + 2e^- | \longrightarrow H_2S(aq) | 0.144 | ||
Sn^{4+}(aq) + 2e^- | \longrightarrow Sn^{2+}(aq) | 0.154 | ||
{SO_4}^{2-}(aq) + 4H^+(aq) + 2e^- | \longrightarrow SO_2(g)+ 2H_2O | 0.155 | ||
Cu^{2+}(aq) + e^- | \longrightarrow Cu^+(aq) | 0.161 | ||
Cu^{2+}(aq) + 2e^- | \longrightarrow Cu(s) | 0.339 | ||
Cu^+(aq) + e^- | \longrightarrow Cu(s) | 0.518 | ||
I_2(s) + 2e^- | \longrightarrow 2I^-(aq) | 0.534 | ||
Fe^{3+}(aq) + e^- | \longrightarrow Fe^{2+}(aq) | 0.769 | ||
{Hg_2}^{2+}(aq) + 2e^- | \longrightarrow 2Hg(l) | 0.796 | ||
Ag^+(aq) + e^- | \longrightarrow Ag(s) | 0.799 | ||
2Hg^{2+}(aq) + 2e^- | \longrightarrow {Hg_{2}}^{2+}(aq) | 0.908 | ||
{NO_3}^-(aq) + 4H^+(aq) + 3e^- | \longrightarrow NO(g) + 2H_2O | 0.964 | ||
{AuCl_4}^-(aq) + 3e^- | \longrightarrow Au(s) + 4Cl^-(aq) | 1.001 | ||
Br_2(l) + 2e^- | \longrightarrow 2Br^-(aq) | 1.077 | ||
O_2(g) + 4H^+(aq) + 4e^- | \longrightarrow 2H_2O | 1.229 | ||
MnO_2(s) + 4H^+(aq) + 2e^- | \longrightarrow Mn^{2+}(aq) + 2H_2O | 1.229 | ||
{Cr_2O_7}^{2-}(aq) + 14H^+(aq) + 6e^- | \longrightarrow 2Cr^{3+}(aq) + 7H_2O | 1.33 | ||
Cl_2(g) + 2e^- | \longrightarrow 2Cl^-(aq) | 1.36 | ||
{ClO_3}^{-}(aq) + 6H^+(aq) + 5e^- | \longrightarrow \frac{1}{2} Cl_2(g) + 3H_2O | 1.458 | ||
Au^{3+}(aq) + 3e^- | \longrightarrow Au(s) | 1.498 | ||
{MnO_4}^{-}(aq) + 8H^+(aq) + 5e^- | \longrightarrow Mn^{2+}(aq) + 4H_2O | 1.512 | ||
PbO_2(s) + {SO_4}^{2-}(aq) + 4H^+(aq) + 2e^- | \longrightarrow PbSO_4(s) + 2H_2O | 1.687 | ||
H_2O_2(aq) + 2H^+(aq) + 2e^- | \longrightarrow 2H_2O | 1.763 | ||
Co^{3+}(aq) + e^- | \longrightarrow Co^{2+}(aq) | 1.953 | ||
F_2(g) + 2e^- \blacktriangleleft ⓘ | \longrightarrow 2F^-(aq) | 2.889 | ||
Basic Solution, [OH^-] = 1 M | ||||
{E^{\circ}}_{red} (V) | ||||
Fe(OH)_2(s) + 2e^- | \longrightarrow Fe(s) + 2OH^-(aq) | -0.891 | ||
2H_2O + 2e^- | \longrightarrow H_2(g) + 2OH^-(aq) | -0.828 | ||
Fe(OH)_3(s) + e^- | \longrightarrow Fe(OH)_2(s) + OH^-(aq) | -0.547 | ||
S(s) + 2e^- | \longrightarrow S^{2-}(aq) | -0.445 | ||
{NO_3}^{-}(aq) + 2H_2O + 3e^- | \longrightarrow NO(g) + 4OH^-(aq) | -0.14 | ||
{NO_3}^-(aq) + H_2O + 2e^- | \longrightarrow {NO_2}^-(aq) + 2OH^-(aq) | 0.004 | ||
{ClO_4}^-(aq) + H_2O + 2e^- | \longrightarrow {ClO_3}^-(aq) + 2OH^-(aq) | 0.398 | ||
O_2(g) + 2H_2O + 4e^- | \longrightarrow 4OH^-(aq) | 0.401 | ||
{ClO_3}^-(aq) + 3H_2O + 6e^- | \longrightarrow Cl^-(aq) + 6OH^-(aq) | 0.614 | ||
ClO^-(aq) + H_2O + 2e^- | \longrightarrow Cl^-(aq) + 2OH^-(aq) | 0.89 |
ⓘ Lithium is the strongest reducing agent.
ⓘ Lithium and fluorine are very dangerous materials to work with.
ⓘ O= strongest oxidizing agent;
R = strongest reducing agent.
ⓘ Fluorine is the strongest oxidizing agent.
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