Electrochemistry Chapter-Wise Test 4

Correct answer Carries: 4.

Wrong Answer Carries: -1.

A cell \( Zn(s) | Zn^{2+}(0.02 \, M) || Fe^{3+}(0.05 \, M), Fe^{2+}(0.01 \, M) | Pt(s) \) operates at 298 K. What is the cell potential? (Given: \( E^\circ_{Zn^{2+}/Zn} = -0.76 \, V \), \( E^\circ_{Fe^{3+}/Fe^{2+}} = 0.77 \, V \))

\( E^\circ_{cell} = 0.77 - (-0.76) = 1.53 \, V \).

\( E_{cell} = 1.53 - \frac{0.059}{1} \log \frac{[Zn^{2+}][Fe^{2+}]}{[Fe^{3+}]} = 1.53 - 0.059 \log \frac{0.02 \times 0.01}{0.05} = 1.53 + 0.0566 = 1.5866 \, V \).

1.53 V
1.5866 V
1.4734 V
1.60 V
2

In a mercury cell, what is the overall cell reaction?

Anode: \( Zn + 2OH^- \rightarrow ZnO + H_2O + 2e^- \).

Cathode: \( HgO + H_2O + 2e^- \rightarrow Hg + 2OH^- \).

Overall: \( Zn + HgO \rightarrow ZnO + Hg \).

\( Zn + HgO + H_2O \rightarrow ZnO + Hg + OH^- \)
\( Zn + 2HgO \rightarrow ZnO + Hg_2 \)
\( Zn + Hg^{2+} \rightarrow Zn^{2+} + Hg \)
\( Zn + HgO \rightarrow ZnO + Hg \)
4

What is the cell constant if the resistance of a 0.05 M KCl solution is 100 Ω and its conductivity is 0.0065 S cm\(^{-1}\)?

\( \kappa = \frac{\text{cell constant}}{R} \), \( 0.0065 = \frac{\text{cell constant}}{100} \), cell constant = 0.65 cm\(^{-1} \).

0.065 cm\(^{-1}\)
0.65 cm\(^{-1}\)
6.5 cm\(^{-1}\)
1.3 cm\(^{-1}\)
2

What is the standard emf of a cell with the reaction \( Mn(s) + Hg^{2+}(aq) \rightarrow Mn^{2+}(aq) + Hg(l) \)? (Given: \( E^\circ_{Mn^{2+}/Mn} = -1.18 \, V \), \( E^\circ_{Hg^{2+}/Hg} = 0.85 \, V \))

\( E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode} = 0.85 - (-1.18) = 2.03 \, V \).

2.03 V
1.18 V
0.33 V
-2.03 V
1

The degree of dissociation of a weak acid is 0.1, and its molar conductivity at infinite dilution is 380 S cm\(^2\) mol\(^{-1}\). What is its molar conductivity at that concentration?

\( \alpha = \frac{\Lambda_m}{\Lambda_m^\circ} \), \( 0.1 = \frac{\Lambda_m}{380} \), \( \Lambda_m = 38 \, S \, cm^2 \, mol^{-1} \).

380 S cm\(^2\) mol\(^{-1}\)
190 S cm\(^2\) mol\(^{-1}\)
76 S cm\(^2\) mol\(^{-1}\)
38 S cm\(^2\) mol\(^{-1}\)
4

What is the standard Gibbs energy change for a cell with \( E^\circ_{cell} = 0.59 \, V \) and 1 electron transferred? (F = 96500 C/mol)

\( \Delta_r G^\circ = -n F E^\circ_{cell} = -1 \times 96500 \times 0.59 = -56935 \, J/mol = -56.935 \, kJ/mol \).

-96.5 kJ/mol
-56.935 kJ/mol
-28.468 kJ/mol
-118.295 kJ/mol
2

How much charge (in coulombs) is required to deposit 0.54 g of nickel from NiSO\(_4\) solution? (Atomic mass of Ni = 54 g/mol, F = 96500 C/mol)

\( Ni^{2+} + 2e^- \rightarrow Ni \). 1 mol Ni (54 g) requires 2F.

Moles = \( \frac{0.54}{54} = 0.01 \, mol \), Charge = \( 0.01 \times 2 \times 96500 = 1930 \, C \).

965 C
4825 C
9650 C
1930 C
4

How much charge (in coulombs) is required to oxidize 1 mole of H\(_2\)O to O\(_2\)? (F = 96500 C/mol)

\( 2H_2O \rightarrow O_2 + 4H^+ + 4e^- \). 1 mol O\(_2\) requires 4F.

Charge = \( 4 \times 96500 = 386000 \, C \).

96500 C
193000 C
289500 C
386000 C
4

A cell \( Sn(s) | Sn^{2+}(0.001 \, M) || I_2(s) | I^-(0.02 \, M) | Pt(s) \) operates at 298 K. What is the cell potential? (Given: \( E^\circ_{Sn^{2+}/Sn} = -0.14 \, V \), \( E^\circ_{I_2/I^-} = 0.54 \, V \))

\( E^\circ_{cell} = 0.54 - (-0.14) = 0.68 \, V \).

\( E_{cell} = 0.68 - \frac{0.059}{2} \log \frac{[Sn^{2+}][I^-]^2}{1} = 0.68 - 0.0295 \log (0.001 \times 0.0004) = 0.68 + 0.103 = 0.783 \, V \).

0.68 V
0.577 V
0.783 V
0.85 V
3

In a fuel cell, the anode reaction produces 0.224 L of H\(_2\)O vapor at STP from H\(_2\). How many coulombs are involved? (F = 96500 C/mol)

Anode: \( H_2 + 2OH^- \rightarrow 2H_2O + 2e^- \). 1 mol H\(_2\)O (22.4 L as vapor) requires 2F.

Moles = \( \frac{0.224}{22.4} = 0.01 \, mol \), Charge = \( 0.01 \times 2 \times 96500 = 1930 \, C \).

965 C
1930 C
3860 C
4825 C
2

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