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Explore popular questions from Electrochemistry for JEE Main. This collection covers Electrochemistry previous year JEE Main questions hand picked by experienced teachers.

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Q 1. At equimolar concentration of {tex} \mathrm { Fe } ^ { 2 + } {/tex} and {tex} \mathrm { Fe } ^ { 3 + } , {/tex} what must {tex} \left[ \mathrm { Ag } ^ { + } \right] {/tex} be so that the voltage of the galvanic cell made from {tex} \mathrm { Ag } ^ { + } / \mathrm { Ag } {/tex} and {tex} \mathrm { Fe } ^ { 3 + } / \mathrm { Fe } ^ { 2 + } {/tex} electrodes equals zero? The reaction is {tex} \mathrm { Fe } ^ { 2 + } + \mathrm { Ag } ^ { + } \rightleftharpoons \mathrm { Fe } ^ { 3 + } + \mathrm { Ag } {/tex}. Determine the equilibrium constant at {tex}25^0 \mathrm { C }{/tex} for the reaction.
Given: {tex} \mathrm E _ { \mathrm { Ag } ^ { + } / \mathrm { Ag } } ^ { \circ } = 0.799 {/tex} volt and {tex} \mathrm E _ { \mathrm { Fe } ^ { + 3 } / \mathrm { Fe } ^ { 2 + } } ^ { \circ } = 0.771 \mathrm { V } {/tex}

3.0

B

2.0

C

4.0

D

1.0

Explanation


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Q 2. Electrolysis of a solution of {tex} \mathrm { HSO } _ { 4 } ^ { -2 } {/tex} ions produces {tex} \mathrm { S } _ { 2 } \mathrm { O } _ { 8 } ^ { - 2 } {/tex} . Assuming 75{tex} \% {/tex} current efficiency, what current should be employed to achieve a production rate of 1 mole {tex} \mathrm { S } _ { 2 } \mathrm { O } _ { 8 }^{2-} {/tex} per hour?

A

43.3{tex} \mathrm { A } {/tex}

71.5{tex} \mathrm { A } {/tex}

C

35.2{tex} \mathrm { A } {/tex}

D

58.3{tex} \mathrm { A } {/tex}

Explanation

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Q 3. How much will the potential of a hydrogen electrode change when its solution initially at {tex} \mathrm { pH } = 0 {/tex} is neutralised to {tex} \mathrm { pH } = 7 {/tex}

A

increase by 0.0591{tex} \mathrm { V } {/tex}

B

decrease by 0.0591{tex} \mathrm { V } {/tex}

C

increase by 0.413{tex} \mathrm { V } {/tex}

decrease by 0.413{tex} \mathrm { V } {/tex}

Explanation

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Q 4. The {tex} E _ { \mathrm { M } ^ { 3 + } / \mathrm { M } ^ { 2 + } } ^ { 0 } {/tex} values for {tex} \mathrm { Cr } , \mathrm { Mn } , \mathrm { Fe } {/tex} and {tex} \mathrm { Co } {/tex} are {tex} - 0.41 {/tex} {tex} + 1.57 , + 0.77 {/tex} and {tex} + 1.97 \mathrm { V } {/tex} respectively. For which one of these metals the change in oxidation state from {tex} + 2 {/tex} to {tex} + 3 {/tex} is easiest?

A

{tex} \mathrm { Co } {/tex}

B

{tex} \mathrm { Mn } {/tex}

C

{tex} \mathbf { F } \mathbf { e } {/tex}

{tex} \mathrm { Cr } {/tex}

Explanation

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Q 5. For the redox change;

In a cell {tex} E _ { \text {cell } } ^ { 0 } {/tex} is 1.10 volt. {tex} \mathrm { E } _ { \text {cell } } {/tex} for the cell would be

1.07{tex} \mathrm { V } {/tex}

B

0.82{tex} \mathrm { V } {/tex}

C

2.14{tex} \mathrm { V } {/tex}

D

180{tex} \mathrm { V } {/tex}

Explanation

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Q 6. In the electrolysis of {tex} \mathrm { CuCl } _ { 2 } {/tex} solution using Cu electrodes, the weight of Cu anode increased by 2{tex} \mathrm { g } {/tex} at cathode. In the anode

A

0.2 mole of {tex} \mathrm { Cu } ^ { 2 + } {/tex} will go into solution.

B

560 {tex} \mathrm { mL } \space \mathrm { O } _ { 2 } {/tex} liberate

C

No loss in weight

2 g of copper goes into solution as {tex} \mathrm { Cu } ^ { 2 + } {/tex}

Explanation

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Q 7. The density of {tex} \mathrm { Cu } {/tex} is {tex} 8.94 \space \mathrm { g } \space \mathrm { cm } ^ { - 3 } . {/tex} The quantity of electricity needed to plate an area {tex} 10 \mathrm { cm } \times 10 \mathrm { cm } {/tex} to a thickness of {tex} 10 ^ { - 2 } \mathrm { cm } {/tex} using {tex} \mathrm { CuSO } _ { 4 } {/tex} solution would be

A

13586{tex} \mathrm { C } {/tex}

27155{tex} \mathrm { C } {/tex}

C

40758{tex} \mathrm { C } {/tex}

D

20348{tex} \mathrm { C } {/tex}

Explanation

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Q 8. A current of 9.65{tex} \mathrm { A } {/tex} is drawn from a Daniel cell for exactly 1{tex} \mathrm { hr } {/tex} . The loss in mass at anode and gain in mass at cathode, respectively are

A

{tex} 11.43 \mathrm { g } , 11.77 \mathrm { g } {/tex}

11.77 g, 11.43{tex} \mathrm { g } {/tex}

C

{tex} 22.86 \mathrm { g } , 23.54 \mathrm { g } {/tex}

D

{tex} 23.54,22.86 \mathrm { g } {/tex}

Explanation

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Q 9. An electrochemical cell stops working after some time because

A

one of the electrodes is eaten away.

electrode potentials of both the electrodes become equal in magnitude.

C

electrode potentials of both electrodes go on decreasing.

D

electrode potentials of both the electrodes go on increasing.

Explanation

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Q 10. The standard emf of the cell {tex} \mathrm { Cd } ( \mathrm { s } ) \left| \mathrm { CdCl } _ { 2 ( 0.1 \mathrm { M } ) } \right| | \mathrm { AgCl } ( \mathrm { s } ) {/tex} {tex} | \mathrm { Ag } ( \mathrm { s } ) {/tex} in which the cell reaction is
{tex} \mathrm { Cd } ( \mathrm { s } ) + 2 \mathrm { AgCl } ( \mathrm { s } ) \rightarrow 2 \mathrm { Ag } ( \mathrm { s } ) + \mathrm { Cd } ^ { 2 + } ( \mathrm { aq } ) + 2 \mathrm { Cl } ^ { - } ( \mathrm { aq } ) {/tex} is 0.6915{tex} \mathrm { V} \space {at } \space 0 ^ { \circ } \mathrm { C } {/tex} and {tex} 0.6753 \mathrm { V\space at } \space 25 ^ { \circ } \mathrm { C } . {/tex} {tex}\triangle {/tex}H of the reaction is

A

{tex} - 176 \mathrm { kJ } {/tex}

B

{tex} - 334.7 \mathrm { kJ } {/tex}

C

{tex} + 123.5 \mathrm { kJ } {/tex}

{tex} 167 \mathrm { kJ } {/tex}

Explanation


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Q 11. If half-cell reaction {tex} \mathrm { A } + e ^ { - } \rightarrow \mathrm { A } ^ { - } {/tex} has a large negative reduction potential, it follows that

A

A is readily reduced

B

A is readily oxidised

C

{tex} \mathrm { A } ^ { - 1 } {/tex} is readily reduced

{tex} \mathrm { A } ^ { - 1 } {/tex} is readily oxidised

Explanation

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Q 12. What will be the emf of the given cell?
{tex}Pt|H_2(P_1)|H^+(aq)|H_2(P_2)|Pt{/tex}

A

{tex} \frac { R T } { F } \ln \frac { P _ { 1 } } { P _ { 2 } } {/tex}

{tex} \frac { R T } { 2 F } \ln \frac { P _ { 1 } } { P _ { 2 } } {/tex}

C

{tex} \frac { R T } { F } \ln \frac { P _ { 2 } } { P _ { 1 } } {/tex}

D

None of these

Explanation

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Q 13. Value of {tex} \mathrm { E } \, \mathrm { H } _ { 2 } \mathrm { O } / \mathrm { H } _ { 2 } ( \mathrm { 1\ atm } ) \mathrm { Pt } {/tex} at 298{tex} \mathrm { K } {/tex} would be

A

{tex} - 0.207 \mathrm { V } {/tex}

B

{tex} + 0.207 \mathrm { V } {/tex}

{tex} - 0.414 \mathrm { V } {/tex}

D

{tex} + 0.414 \mathrm { V } {/tex}

Explanation

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Q 14. Conductivity (units Siemen's S) is directly proportional to the area of the vessel and the concentration of the solution in it and is inversely proportional to the length of the vessel, then the unit of constant of proportionality is

A

{tex} \mathrm { S \space m } \, \mathrm { mol } ^ { - 1 } {/tex}

{tex}\, \mathrm { S \, m } ^ { 2 } \mathrm { mol } ^ { - 1 } {/tex}

C

{tex} \mathrm { S } ^ { - 2 } \mathrm { m } ^ { 2 } \mathrm { mol } {/tex}

D

{tex} \mathrm { S } ^ { 2 } \mathrm { m } ^ { 2 } \mathrm { mol } ^ { - 2 } {/tex}

Explanation

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Q 15. The standard e.m.f. of a cell involving one electron change is found to be 0.591{tex} \mathrm { V } {/tex} at {tex} 25 ^ { \circ } \mathrm { C } {/tex} . The equilibrium constant of the reaction is {tex} \left( \mathrm { F } = 96,500 \mathrm { C } \mathrm { mol } ^ { - 1 } ; \mathrm { R } = 8.314 \mathrm { JK } ^ { - 1 } \mathrm { mol } ^ { - 1 } \right) {/tex}

{tex} 1.0 \times 10 ^ { 10 } {/tex}

B

{tex} 1.0 \times 10 ^ { 5 } {/tex}

C

{tex} 1.0 \times 10 ^ { 1 } {/tex}

D

{tex} 1.0 \times 10 ^ { 30 } {/tex}

Explanation



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Q 16. For a cell reaction involving a two-electron change, the standard e.m.f. of the cell is found to be {tex} \mathrm {0.295 V } {/tex} at {tex} 25 ^ { \circ } \mathrm { C } {/tex} . The equilibrium constant of the reaction at {tex} 25 ^ { \circ } \mathrm { C } {/tex} will be

A

{tex} 29.5 \times 10 ^ { - 2 } {/tex}

B

{tex}10{/tex}

{tex} 1 \times 10 ^ { 10 } {/tex}

D

{tex} 1 \times 10 ^ { - 10 } {/tex}

Explanation



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Q 17. The highest electrical conductivity of the following aqueous solutions is of

{tex}0.1\, \mathrm { M } {/tex} difluoroacetic acid

B

{tex}0.1\, \mathrm { M } {/tex} fluoroacetic acid

C

{tex}0.1\, \mathrm { M } {/tex} chloroacetic acid

D

{tex}0.1\, \mathrm { M } {/tex} acetic acid

Explanation


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Q 18. When during electrolysis of a solution of AgNO{tex}_3{/tex}, 9650 coulombs of charge pass through the electroplating bath, the mass of silver deposited on the cathode will be

{tex}10.8\ \mathrm g {/tex}

B

{tex}21.6\ \mathrm g {/tex}

C

{tex}108\ \mathrm { g } {/tex}

D

{tex}1.08\ \mathrm { g } {/tex}

Explanation



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Q 19. Two Faraday of electricity is passed through a solution of CuSO{tex}_4{/tex}, The mass of copper deposited at the cathode is (at. mass of Cu = 63.5 amu)

A

2 g

B

127 g

C

0 g

63.5 g

Explanation

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Q 20. EMF of a cell in terms of reduction potential of its left and right electrodes is

A

{tex} E = E _ { \mathrm { left } } - E _ { \mathrm { right } } {/tex}

B

{tex} E = E _ { \mathrm { left } } + E _ { \mathrm { right } } {/tex}

{tex} E = E _ { \text {right } } - E _ { \text {left } } {/tex}

D

{tex} E = - \left( E _ { \text {right } } + E _ { \text {left } } \right) {/tex}

Explanation

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Q 21. What will be the emf for the given cell
{tex} \mathrm { Pt } \left| \mathrm { H } _ { 2 } \left( \mathrm { P } _ { 1 } \right) \right| \mathrm { H } ^ { + } ( \mathrm { aq } ) | | \mathrm { H } _ { 2 } \left( \mathrm { P } _ { 2 } \right) | \mathrm { Pt } {/tex}

A

{tex} \frac { R T } { F } \log _ { \mathrm { e } } \frac { P _ { \mathrm { l } } } { P _ { 2 } } {/tex}

{tex} \frac { R T } { 2 F } \log _ { e } \frac { P _ { 1 } } { P _ { 2 } } {/tex}

C

{tex} \frac { R T } { F } \log _ { \mathrm { e } } \frac { P _ { 2 } } { P _ { 1 } } {/tex}

D

None of these.

Explanation

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Q 22. Resistance of a conductivity cell filled with a solution of an electrolyte of concentration {tex}0.1\, \mathrm { M } {/tex} is {tex}100\, \Omega {/tex} . The conductivity of this solution is {tex} 1.29 \mathrm { S } \mathrm { m } ^ { - 1 } . {/tex} Resistance of the same cell when filled with {tex} 0.2\mathrm { M } {/tex} of the same solution is {tex} 520\Omega {/tex} . The molar conductivity of {tex} 0.2\mathrm { M } {/tex} solution of electrolyte will be

A

{tex} 1.24 \times 10 ^ { - 4 } \mathrm { S } \mathrm { m } ^ { 2 } \mathrm { mol } ^ { - 1 } {/tex}

{tex} 12.4 \times 10 ^ { - 4 } \mathrm { S } \mathrm { m } ^ { 2 } \mathrm { mol } ^ { - 1 } {/tex}

C

{tex} 124 \times 10 ^ { - 4 } \mathrm { Sm } ^ { 2 } \mathrm { mol } ^ { - 1 } {/tex}

D

{tex} 1240 \times 10 ^ { - 4 } \mathrm { S } \mathrm { m } ^ { 2 } \mathrm { mol } ^ { - 1 } {/tex}

Explanation



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Q 23. When the sample of copper with zinc impurity is to be purified by electrolysis, the appropriate electrodes are

A

Cathode - pure zinc {tex} \quad {/tex} Anode - pure copper

B

Cathode - impure sample {tex} \quad {/tex} Anode - pure copper

C

Cathode - impure zinc {tex} \quad {/tex} Anode - impure sample

Cathode -pure copper {tex} \quad {/tex} Anode - impure sample.

Explanation

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Q 24. The standard reduction potentials for {tex} \mathrm { Zn } ^ { 2 + } / \mathrm { Zn } {/tex} , {tex} \mathrm { Ni } ^ { 2 + } / \mathrm { Ni } {/tex} and {tex} \mathrm { Fe } ^ { 2 + } / \mathrm { Fe } {/tex} are {tex} - 0.76 , - 0.23 {/tex} and {tex} - 0.44 \mathrm { V } {/tex} respectively.
The reaction {tex} X + Y ^ { 2 + } \longrightarrow X ^ { 2 + } + Y {/tex} will be spontaneous when:

A

{tex} \mathrm { X } = \mathrm { Ni } , \mathrm { Y } = \mathrm { Fe } {/tex}

B

{tex} \mathrm { X } = \mathrm { Ni } , \mathrm { Y } = \mathrm { Zn } {/tex}

C

{tex} \mathrm { X } = \mathrm { Fe } , \mathrm { Y } = \mathrm { Zn } {/tex}

{tex} \mathrm { X } = \mathrm { Zn } , \mathrm { Y } = \mathrm { Ni } {/tex}

Explanation





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Q 25. In a fuel cell methanol is used as fuel and oxygen gas is used as an oxidizer. The reaction is
{tex} \mathrm { CH } _ { 3 } \mathrm { OH } ( l ) + 3 / 2 \mathrm { O } _ { 2 } ( \mathrm { g } ) \longrightarrow \mathrm { CO } _ { 2 } ( \mathrm { g } ) + 2 \mathrm { H } _ { 2 } \mathrm { O } ( l ) {/tex}
At 298{tex} \mathrm { K } {/tex} standard Gibb's energies of formation for {tex} \mathrm { CH } _ { 3 } \mathrm { OH } ( l ) {/tex}, {tex} \mathrm { H } _ { 2 } \mathrm { O } ( l ) {/tex} and and {tex} \mathrm { CO } _ { 2 } ( g ) {/tex} are {tex} - 166.2 - 237.2 {/tex} and {tex} - 394.4 \mathrm { kJ } {/tex} {tex} \mathrm { mol } ^ { - 1 } {/tex} respectively. If standard enthalpy of combustion of methonal is {tex} - 726 \mathrm { kJ } \mathrm { mol } ^ { - 1 } {/tex} , efficiency of the fuel cell will be:

A

{tex}87\, \% {/tex}

B

{tex}90\, \% {/tex}

{tex}97\, \% {/tex}

D

{tex}80\, \% {/tex}

Explanation