Electrochemistry Chapter-Wise Test 1

Correct answer Carries: 4.

Wrong Answer Carries: -1.

The degree of dissociation of a weak electrolyte is 0.05, and its molar conductivity is 19 S cm\(^2\) mol\(^{-1}\). What is its \( \Lambda_m^\circ \)?

\( \alpha = \frac{\Lambda_m}{\Lambda_m^\circ} \), \( 0.05 = \frac{19}{\Lambda_m^\circ} \), \( \Lambda_m^\circ = 380 \, S \, cm^2 \, mol^{-1} \).

95 S cm\(^2\) mol\(^{-1}\)
190 S cm\(^2\) mol\(^{-1}\)
9.5 S cm\(^2\) mol\(^{-1}\)
380 S cm\(^2\) mol\(^{-1}\)
4

In the electrolysis of aqueous K\(_2\)SO\(_4\) with inert electrodes, what gas is produced at the anode?

Anode: \( 2H_2O \rightarrow O_2 + 4H^+ + 4e^- \). Oxygen gas is produced.

H\(_2\)
SO\(_2\)
O\(_2\)
Cl\(_2\)
3

In a fuel cell, what is the cathode reaction?

Cathode: \( O_2 + 4H^+ + 4e^- \rightarrow 2H_2O \).

\( H_2 + 2OH^- \rightarrow 2H_2O + 2e^- \)
\( O_2 + 2H_2O + 4e^- \rightarrow 4OH^- \)
\( H_2 \rightarrow 2H^+ + 2e^- \)
\( O_2 + 4H^+ + 4e^- \rightarrow 2H_2O \)
4

How much time (in seconds) is required to deposit 0.635 g of copper from CuSO\(_4\) solution using a current of 0.5 A? (Atomic mass of Cu = 63.5 g/mol, F = 96500 C/mol)

Moles of Cu = \( \frac{0.635}{63.5} = 0.01 \, mol \).

Charge = \( 0.01 \times 2 \times 96500 = 1930 \, C \).

\( t = \frac{Q}{I} = \frac{1930}{0.5} = 3860 \, s \).

1930 s
3860 s
965 s
4825 s
2

A cell operates with \( E_{cell} = 1.50 \, V \) at 298 K when \( [Anode] = 0.001 \, M \) and \( [Cathode] = 0.1 \, M \). If \( E^\circ_{cell} = 1.44 \, V \), what is the reaction quotient \( Q \)?

\( E_{cell} = E^\circ_{cell} - \frac{0.059}{n} \log Q \), \( 1.50 = 1.44 - \frac{0.059}{2} \log Q \).

\( 0.06 = -0.0295 \log Q \), \( \log Q = -\frac{0.06}{0.0295} = -2.034, Q = 10^{-2.034} \approx 0.0092 \).

Since \( Q = \frac{[Anode]}{[Cathode]} = \frac{0.001}{0.1} = 0.01 \), matches approximately.

0.1
1.0
0.001
0.01
4

In a dry cell, what is the oxidation state of manganese in the cathode product MnO(OH)?

Cathode: \( MnO_2 + NH_4^+ + e^- \rightarrow MnO(OH) + NH_3 \).

In \( MnO_2 \), Mn = +4; in \( MnO(OH) \), Mn + 2(-2) + 1 = 0, Mn = +3.

+3
+4
+2
+1
1

What is the limiting molar conductivity of CaCl\(_2\) in water at 298 K, given \( \lambda^\circ_{Ca^{2+}} = 119 \, S \, cm^2 \, mol^{-1} \), \( \lambda^\circ_{Cl^-} = 76.3 \, S \, cm^2 \, mol^{-1} \)?

\( \Lambda_m^\circ = \lambda^\circ_{Ca^{2+}} + 2 \lambda^\circ_{Cl^-} = 119 + 2 \times 76.3 = 271.6 \, S \, cm^2 \, mol^{-1} \).

195.3 S cm\(^2\) mol\(^{-1}\)
152.6 S cm\(^2\) mol\(^{-1}\)
271.6 S cm\(^2\) mol\(^{-1}\)
347.9 S cm\(^2\) mol\(^{-1}\)
3

What is the emf of a cell \( Zn(s) | Zn^{2+}(0.001 \, M) || H^+(1 \, M) | H_2(g)(1 \, bar) | Pt(s) \) at 298 K? (Given: \( E^\circ_{Zn^{2+}/Zn} = -0.76 \, V \), \( E^\circ_{H^+/H_2} = 0.00 \, V \))

\( E^\circ_{cell} = 0.00 - (-0.76) = 0.76 \, V \).

\( E_{cell} = 0.76 - \frac{0.059}{2} \log \frac{0.001}{1^2} = 0.76 + 0.0885 = 0.8485 \, V \).

0.76 V
0.6715 V
0.80 V
0.8485 V
4

The molar conductivity of a strong electrolyte at infinite dilution is 240 S cm\(^2\) mol\(^{-1}\). If its molar conductivity at 0.01 M is 228 S cm\(^2\) mol\(^{-1}\), what is the degree of dissociation at this concentration?

For a strong electrolyte, \( \alpha = \frac{\Lambda_m}{\Lambda_m^\circ} \), but here it’s less than 1 due to ion interaction.

\( \alpha = \frac{228}{240} = 0.95 \).

0.95
1.00
0.90
0.85
1

The resistance of a conductivity cell with 0.02 M NaCl solution is 500 Ω, and its conductivity is 0.0024 S cm\(^{-1}\). What is the cell constant?

\( \kappa = \frac{\text{cell constant}}{R} \), \( 0.0024 = \frac{\text{cell constant}}{500} \), cell constant = 1.2 cm\(^{-1} \).

0.24 cm\(^{-1}\)
1.2 cm\(^{-1}\)
2.4 cm\(^{-1}\)
0.12 cm\(^{-1}\)
2

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