Electrochemistry Chapter-Wise Test 14

Correct answer Carries: 4.

Wrong Answer Carries: -1.

A hydrogen electrode operates at 298 K with \( P_{H_2} = 0.5 \, atm \) and pH = 3. What is its potential? (Given: \( E^\circ_{H^+/H_2} = 0.00 \, V \))

\( E = E^\circ - \frac{0.059}{2} \log \frac{P_{H_2}}{[H^+]^2} \), \( [H^+] = 10^{-3} \).

\( E = 0 - 0.0295 \log \frac{0.5}{10^{-6}} = 0 - 0.0295 \times 5.301 = -0.1564 \, V \).

-0.177 V
-0.118 V
-0.295 V
-0.1564 V
4

In electrolysis of molten NaF, 0.23 g of Na (atomic mass 23 g/mol) is deposited. What volume of F\(_2\) gas (STP) is produced at the anode? (F = 96500 C/mol)

Cathode: \( Na^+ + e^- \rightarrow Na \), Moles = \( \frac{0.23}{23} = 0.01 \, mol \), Charge = \( 0.01 \times 96500 = 965 \, C \).

Anode: \( 2F^- \rightarrow F_2 + 2e^- \), Moles F\(_2\) = \( \frac{0.01}{2} = 0.005 \, mol \), Volume = \( 0.005 \times 22.4 = 0.112 \, L \).

0.224 L
0.056 L
0.448 L
0.112 L
3

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

The cathode in a lead storage battery is lead dioxide (PbO\(_2\)).

Pb
PbO\(_2\)
PbSO\(_4\)
H\(_2\)SO\(_4\)
2

A current of 0.2 A deposits 0.127 g of Cu from CuSO\(_4\) in 9650 s. What is the current required to deposit 0.27 g of Al from AlCl\(_3\) in the same time? (Atomic masses: Cu = 63.5 g/mol, Al = 27 g/mol, F = 96500 C/mol)

Cu: Charge = \( 0.2 \times 9650 = 1930 \, C \), Moles = \( \frac{0.127}{63.5} = 0.002 \, mol \), Charge = \( 0.002 \times 2 \times 96500 = 1930 \, C \), matches.

Al: \( Al^{3+} + 3e^- \rightarrow Al \), Moles = \( \frac{0.27}{27} = 0.01 \, mol \), Charge = \( 0.01 \times 3 \times 96500 = 2895 \, C \).

\( I = \frac{2895}{9650} = 0.3 \, A \).

0.3 A
0.2 A
0.4 A
0.1 A
1

A cell \( Ni(s) | Ni^{2+}(0.002 \, M) || Cl_2(g)(0.5 \, atm) | Cl^-(0.05 \, M) | Pt(s) \) operates at 298 K. What is the cell potential? (Given: \( E^\circ_{Ni^{2+}/Ni} = -0.25 \, V \), \( E^\circ_{Cl_2/Cl^-} = 1.36 \, V \))

\( E^\circ_{cell} = 1.36 - (-0.25) = 1.61 \, V \).

\( E_{cell} = 1.61 - \frac{0.059}{2} \log \frac{[Ni^{2+}][Cl^-]^2}{P_{Cl_2}} = 1.61 - 0.0295 \log \frac{0.002 \times 0.0025}{0.5} = 1.61 + 0.084 = 1.694 \, V \).

1.61 V
1.526 V
1.694 V
1.78 V
3

What is the potential of a hydrogen electrode in a solution with pH = 10 at 298 K? (Given: \( E^\circ_{H^+/H_2} = 0.00 \, V \))

\( E = E^\circ - \frac{0.059}{n} \log \frac{1}{[H^+]} \), \( [H^+] = 10^{-10} \), \( n = 1 \).

\( E = 0 - 0.059 \times 10 = -0.59 \, V \).

0.00 V
-0.29 V
0.59 V
-0.59 V
4

What is the emf of the cell \( Co(s) | Co^{2+}(0.01 \, M) || Ag^+(0.001 \, M) | Ag(s) \) at 298 K? (Given: \( E^\circ_{Co^{2+}/Co} = -0.28 \, V \), \( E^\circ_{Ag^+/Ag} = 0.80 \, V \))

\( E^\circ_{cell} = 0.80 - (-0.28) = 1.08 \, V \).

\( E_{cell} = 1.08 - \frac{0.059}{2} \log \frac{[Co^{2+}]}{[Ag^+]^2} = 1.08 - 0.0295 \log \frac{0.01}{0.000001} = 1.08 - 0.177 = 0.903 \, V \).

1.08 V
0.903 V
1.257 V
0.726 V
2

In the electrolysis of dilute H\(_2\)SO\(_4\) with Pt electrodes, what gas is liberated at the cathode?

Cathode: \( 2H_2O + 2e^- \rightarrow H_2 + 2OH^- \). Hydrogen gas is liberated.

O\(_2\)
SO\(_2\)
H\(_2\)S
H\(_2\)
4

In a fuel cell using H\(_2\) and O\(_2\), what is the anode reaction?

Anode: \( H_2 + 2OH^- \rightarrow 2H_2O + 2e^- \) in basic medium.

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

In a mercury cell, what is the product at the anode during discharge?

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

ZnO
Hg
HgO
Zn
1

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