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  4. Electrochemistry Chapter-Wise Test 3

Electrochemistry Chapter-Wise Test 3

Correct answer Carries: 4.

Wrong Answer Carries: -1.

During electrolysis of aqueous Na\(_2\)SO\(_4\) with inert electrodes, 0.224 L of gas (STP) is collected at the cathode. How many coulombs were passed? (F = 96500 C/mol)

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

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

965 C
2895 C
1930 C
4825 C
3

What is the emf of the cell \( Cd(s) | Cd^{2+}(0.01 \, M) || Ni^{2+}(0.1 \, M) | Ni(s) \) at 298 K? (Given: \( E^\circ_{Cd^{2+}/Cd} = -0.40 \, V \), \( E^\circ_{Ni^{2+}/Ni} = -0.25 \, V \))

\( E^\circ_{cell} = -0.25 - (-0.40) = 0.15 \, V \).

\( E_{cell} = 0.15 - \frac{0.059}{2} \log \frac{0.01}{0.1} = 0.15 + 0.0295 = 0.1795 \, V \).

0.15 V
0.1795 V
0.1205 V
0.20 V
2

In a lead storage battery, what is the anode material?

The anode in a lead storage battery is lead (Pb).

PbO\(_2\)
PbSO\(_4\)
H\(_2\)SO\(_4\)
Pb
4

What is the standard cell potential for a galvanic cell where iron is oxidized and silver ions are reduced? (Given: \( E^\circ_{Fe^{2+}/Fe} = -0.44 \, V \), \( E^\circ_{Ag^+/Ag} = 0.80 \, V \))

Reaction: \( Fe(s) + 2Ag^+(aq) \rightarrow Fe^{2+}(aq) + 2Ag(s) \).

\( E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode} = 0.80 - (-0.44) = 1.24 \, V \).

1.24 V
0.36 V
1.64 V
-1.24 V
1

The resistance of a conductivity cell with 0.01 M NaCl solution is 250 Ω, and its conductivity is 0.0012 S cm\(^{-1}\). What is the cell constant?

\( \kappa = \frac{\text{cell constant}}{R} \), \( 0.0012 = \frac{\text{cell constant}}{250} \), cell constant = 0.3 cm\(^{-1} \).

0.12 cm\(^{-1}\)
1.2 cm\(^{-1}\)
0.3 cm\(^{-1}\)
3.0 cm\(^{-1}\)
3

A lead storage battery is discharged with 2 A for 5 hours. What is the mass of PbO\(_2\) (molar mass 239 g/mol) consumed at the cathode? (F = 96500 C/mol)

Charge = \( 2 \times 5 \times 3600 = 36000 \, C \).

Cathode: \( PbO_2 + SO_4^{2-} + 4H^+ + 2e^- \rightarrow PbSO_4 + 2H_2O \). 1 mol PbO\(_2\) requires 2F.

Faradays = \( \frac{36000}{96500} = 0.373 \, F \), Moles = \( \frac{0.373}{2} = 0.1865 \, mol \), Mass = \( 0.1865 \times 239 = 44.57 \, g \).

22.28 g
89.14 g
23.9 g
44.57 g
4

The limiting molar conductivity of KBr is 151.8 S cm\(^2\) mol\(^{-1}\). If \( \lambda^\circ_{K^+} = 73.5 \, S \, cm^2 \, mol^{-1} \), what is \( \lambda^\circ_{Br^-} \)?

\( \Lambda_m^\circ = \lambda^\circ_{K^+} + \lambda^\circ_{Br^-} \).

\( 151.8 = 73.5 + \lambda^\circ_{Br^-} \), \( \lambda^\circ_{Br^-} = 78.3 \, S \, cm^2 \, mol^{-1} \).

78.3 S cm\(^2\) mol\(^{-1}\)
151.8 S cm\(^2\) mol\(^{-1}\)
73.5 S cm\(^2\) mol\(^{-1}\)
38.4 S cm\(^2\) mol\(^{-1}\)
1

The conductivity of a 0.008 M solution is 0.00104 S cm\(^{-1}\). What is its molar conductivity?

\( \Lambda_m = \frac{\kappa \times 1000}{c} = \frac{0.00104 \times 1000}{0.008} = 130 \, S \, cm^2 \, mol^{-1} \).

65 S cm\(^2\) mol\(^{-1}\)
130 S cm\(^2\) mol\(^{-1}\)
260 S cm\(^2\) mol\(^{-1}\)
104 S cm\(^2\) mol\(^{-1}\)
2

The conductivity of a 0.025 M solution is 0.00325 S cm\(^{-1}\). What is its molar conductivity?

\( \Lambda_m = \frac{\kappa \times 1000}{c} = \frac{0.00325 \times 1000}{0.025} = 130 \, S \, cm^2 \, mol^{-1} \).

65 S cm\(^2\) mol\(^{-1}\)
130 S cm\(^2\) mol\(^{-1}\)
260 S cm\(^2\) mol\(^{-1}\)
32.5 S cm\(^2\) mol\(^{-1}\)
2

What is the equilibrium constant for a cell reaction with \( E^\circ_{cell} = 0.236 \, V \) at 298 K involving 2 electrons?

\( E^\circ_{cell} = \frac{0.059}{n} \log K_c \).

\( 0.236 = \frac{0.059}{2} \log K_c \), \( \log K_c = 8, K_c = 10^8 \).

10\(^4\)
10\(^6\)
10\(^7\)
10\(^8\)
4

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