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JEE Main

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. An ammeter and copper voltmeter are connected in series in an electric circuit through which a constant direct current flows. The ammeter shows {tex}0.525 {/tex} amp. If {tex}0.6354 {/tex} g of {tex} \mathrm { Cu } {/tex} is deposited in one hour, what is percentage error of ammeter? [ At. wt. of {tex} \mathrm { Cu } = 63.54.{/tex}]

2

B

3

C

4

D

5

Explanation

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Q 3. Cd amalgam is prepared by electrolysis of a solution of {tex} \mathrm { CdCl } _ { 2 } {/tex} using a mercury cathode. How many minute long should a current of {tex} \mathrm{5} {/tex}amp is passed in order to prepare {tex} 12 \% \mathrm { Cd }- \mathrm{Hg} {/tex} amalgam on a cathode of {tex} 2.56 {/tex} g mercury? [At.wt. of {tex} \mathrm { Cd } = 112.40 . ] {/tex}

A

4

B

3

2

D

1

Explanation

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Q 4. 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 5. 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 6. 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 7. 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 8. An aqueous solution containing {tex} \mathrm { Na } ^ { + } , \mathrm { Sn } ^ { 2 + } , \mathrm { Cl } ^ { - } {/tex} and {tex} \mathrm { SO } _ { 4 } ^ { 2 - } {/tex} ions, all at unit concentration, is electrolysed between a silver anode and a platinum cathode. What changes occur at the electrodes when current is passed through the cell? Given:
{tex} E _ { \mathrm { Ag } ^ { + } / \mathrm { Ag } } ^ { \circ } = 0.799 \mathrm { V } {/tex}

A

{tex} \mathrm { Sn } ^ { 2 + } {/tex} is reduced and {tex} \mathrm { Cl } ^ { - } {/tex} is oxidised.

B

Ag is oxidised and {tex} \mathrm { Sn } ^ { 2 + } {/tex} is reduced.

{tex} \mathrm { Sn } ^ { 2 + } {/tex} is reduced and {tex} \mathrm { Sn } ^ { 2 + } {/tex} is oxidised

D

{tex} \mathrm { H } ^ { + } {/tex} is reduced and {tex} \mathrm { Sn } ^ { 2 + } {/tex} is oxidised.

Explanation



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Q 9. The limiting molar conductivities {tex} \Lambda ^ { \circ } {/tex} for {tex} \mathrm { NaCl } , \mathrm { KBr } {/tex} and {tex} \mathrm { KCl } {/tex} are {tex} 126,152 {/tex} and {tex} 150 \mathrm { S } \space \mathrm { cm } ^ { 2 } \mathrm { mol } ^ { - 1 } {/tex} respectively. The {tex} \Lambda ^ { \circ } {/tex} for {tex} \mathrm { NaBr } \left( \mathrm { S } \space \mathrm { cm } ^ { 2 } \mathrm { mol } ^ { - 1 } \right) {/tex} is

A

302

B

176

C

278

128

Explanation

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Q 10. 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 11. 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 12. 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 13. 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 14. Four alkali metals {tex} \mathrm { A } , \mathrm { B } , \mathrm { C } {/tex} and {tex} \mathrm { D } {/tex} are having respectively standard electrode potentials as {tex} - 3.05 , - 1.66 , - 0.40 {/tex} and {tex} -0.80 \mathrm { V } . {/tex} Which one will be most reducing?

{tex} A {/tex}

B

{tex} B {/tex}

C

{tex} C {/tex}

D

{tex} D {/tex}

Explanation

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Q 15. 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 16. 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 17. A standard hydrogen electrode has zero electrode potential because

A

hydrogen is easier to oxidise.

this electrode potential is assumed to be zero.

C

hydrogen atom has only one electron.

D

hydrogen is the lightest element.

Explanation

Hydrogen is used as standard electrode and other electrodes potential is measured w.r.t. to hydrogen so potential of hydrogen is assumed to zero for standard measurements

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Q 18. 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 19. 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 20. 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