Electrochemistry Chapter-Wise Test 11

Correct answer Carries: 4.

Wrong Answer Carries: -1.

The conductivity of a 0.002 M weak electrolyte solution is 8 × 10\(^{-5}\) S cm\(^{-1}\). What is its molar conductivity?

\( \Lambda_m = \frac{\kappa \times 1000}{c} = \frac{8 \times 10^{-5} \times 1000}{0.002} = 40 \, S \, cm^2 \, mol^{-1} \).

20 S cm\(^2\) mol\(^{-1}\)
40 S cm\(^2\) mol\(^{-1}\)
80 S cm\(^2\) mol\(^{-1}\)
4 S cm\(^2\) mol\(^{-1}\)
2

In a fuel cell, what is the oxidizing agent?

Reaction: \( 2H_2 + O_2 \rightarrow 2H_2O \). O\(_2\) is reduced, so it’s the oxidizing agent.

H\(_2\)
H\(_2\)O
H\(^+\)
O\(_2\)
4

A mercury cell produces 0.5 g of Hg (atomic mass 200 g/mol) at the cathode. What mass of Zn (atomic mass 68 g/mol) is oxidized at the anode? (F = 96500 C/mol)

Cathode: \( HgO + H_2O + 2e^- \rightarrow Hg + 2OH^- \), Moles = \( \frac{0.5}{200} = 0.0025 \, mol \), Charge = \( 0.0025 \times 2 \times 96500 = 482.5 \, C \).

Anode: \( Zn \rightarrow Zn^{2+} + 2e^- \), Moles Zn = \( 0.0025 \, mol \), Mass = \( 0.0025 \times 68 = 0.17 \, g \).

0.34 g
0.085 g
0.68 g
0.17 g
4

How many Faradays are required to deposit 27 g of aluminum from molten Al\(_2\)O\(_3\)? (Atomic mass of Al = 27 g/mol)

\( Al^{3+} + 3e^- \rightarrow Al \). 1 mol Al (27 g) requires 3F.

Moles = \( \frac{27}{27} = 1 \, mol \), Charge = \( 1 \times 3 = 3F \).

1 F
3 F
2 F
4 F
2

The emf of a cell \( Fe(s) | Fe^{2+}(0.001 \, M) || Cu^{2+}(0.1 \, M) | Cu(s) \) at 298 K is (Given: \( E^\circ_{Fe^{2+}/Fe} = -0.44 \, V \), \( E^\circ_{Cu^{2+}/Cu} = 0.34 \, V \))?

\( E^\circ_{cell} = 0.34 - (-0.44) = 0.78 \, V \).

\( E_{cell} = 0.78 - \frac{0.059}{2} \log \frac{0.001}{0.1} = 0.78 + 0.059 = 0.839 \, V \).

0.78 V
0.839 V
0.721 V
0.90 V
2

A galvanic cell has \( E^\circ_{cell} = 0.62 \, V \). If the cell potential becomes 0.68 V at 298 K when \( [Oxidized] = 0.01 \, M \) and \( [Reduced] = 0.1 \, M \), how many electrons are transferred?

\( E_{cell} = E^\circ_{cell} - \frac{0.059}{n} \log \frac{[Ox]}{[Red]} \), \( 0.68 = 0.62 - \frac{0.059}{n} \log \frac{0.01}{0.1} \).

\( 0.06 = \frac{0.059}{n} \times 1 \), \( n = \frac{0.059}{0.06} \approx 1 \).

1
2
3
4
1

In a lead storage battery during discharge, what is the oxidation state of lead in the cathode product?

Cathode: \( PbO_2 + SO_4^{2-} + 4H^+ + 2e^- \rightarrow PbSO_4 + 2H_2O \). In PbSO\(_4\), Pb = +2.

+2
+4
0
+1
1

In a mercury cell, 0.34 g of Zn (atomic mass 68 g/mol) is oxidized at the anode. What mass of Hg (atomic mass 200 g/mol) is produced at the cathode? (F = 96500 C/mol)

Anode: \( Zn \rightarrow Zn^{2+} + 2e^- \), Moles = \( \frac{0.34}{68} = 0.005 \, mol \), Charge = \( 0.005 \times 2 \times 96500 = 965 \, C \).

Cathode: \( HgO + H_2O + 2e^- \rightarrow Hg + 2OH^- \), Moles Hg = \( 0.005 \, mol \), Mass = \( 0.005 \times 200 = 1.0 \, g \).

1.0 g
2.0 g
0.5 g
1.5 g
1

The standard Gibbs energy change for a cell reaction is -212.27 kJ/mol, and 2 electrons are transferred. What is the standard emf of the cell? (F = 96500 C/mol)

\( \Delta_r G^\circ = -n F E^\circ_{cell} \).

\( -212270 = -2 \times 96500 \times E^\circ_{cell} \), \( E^\circ_{cell} = 1.1 \, V \).

0.55 V
1.10 V
2.20 V
0.80 V
2

What is the standard emf of a cell with the reaction \( Co(s) + Ni^{2+}(aq) \rightarrow Co^{2+}(aq) + Ni(s) \)? (Given: \( E^\circ_{Co^{2+}/Co} = -0.28 \, V \), \( E^\circ_{Ni^{2+}/Ni} = -0.25 \, V \))

\( E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode} = -0.25 - (-0.28) = 0.03 \, V \).

0.03 V
0.53 V
-0.03 V
0.25 V
1

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