Electrochemistry Questions — JEE Chemistry

Q1

Galvanization is applying a coating of :

A Cr

B Cu

C Zn

D Pb

Correct Answer

Option C

Solution

Galvanization is the process by which zinc is coated over corrosive (easily rusted) metals to prevent them from corrosion.

Q2

In 3d series, the metal having the highest M2+/M standard electrode potential is :

A Cr

B Fe

C Cu

D Zn

Correct Answer

Option C

Solution

Cr+2/Cr $\to$ –0.90 V Fe+2/Fe $\to$ –0.44 V Cu+2/Cu $\to$ +0.34 V Zn+2/Zn $\to$ -0.76 V So Ans. is Cu+2/Cu

Q3

The anodic half-cell of lead-acid battery is recharged using electricity of 0.05 Faraday. The amount of PbSO4 electrolyzed in g during the process is : (Molar mass of PbSO4 = 303 g mol

-

1)

A 22.8

B 15.2

C 7.6

D 11.4

Correct Answer

Option C

Solution

Pb(s) + SO

_4^{ - 2}

$\to$ PbSO4 + 2e $-$

{{{n_{PbS{O_4}}}} \over 1} = {{{n_{e - }}} \over 2}

$\Rightarrow$

{{{n_{PbS{O_4}}}} \over 1} = {{0.05} \over 2}

$\therefore$ Weight of PbSO4 $=$

{{0.05} \over 2} \times 303 = 7.6g

Q4

Match List I with List II .tg .tg LIST I (Cell) LIST II (Use/Property/Reaction) A. Leclanche cell I. Converts energy of combustion into electrical energy B. Ni - Cd cell II. Does not involve any ion in solution and is used in hearing aids C. Fuel cell III. Rechargeable D. Mercury cell IV. Reaction at anode

\mathrm{Zn} \rightarrow \mathrm{Zn}^{2+}+2 \mathrm{e}^{-}

Choose the correct answer from the options given below :

A A-III, B-I, C-IV, D-II

B A-I, B-II, C-III, D-IV

C A-IV, B-III, C-I, D-II

D A-II, B-III, C-IV, D-I

Correct Answer

Option C

Solution

To find the correct match between List I (Cell) and List II (Use/Property/Reaction), let's first understand each item and its corresponding match: List I (Cell): Leclanché cell: This is a primary cell (non-rechargeable) widely used in flashlights and other portable devices.

It's not designed for recharging.

Ni - Cd cell: Nickel-Cadmium (NiCd) batteries are rechargeable and known for being used in portable electronics, tools, and various battery-operated devices.

Fuel cell: Converts chemical energy, from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent.

It converts energy of combustion (such as hydrogen) into electrical energy directly.

Mercury cell: A type of battery that uses mercury oxide.

It's known for its stable output voltage, making it suitable for devices like hearing aids.

However, the reaction described in the list II does not pertain to the mercury cell but more closely to the Leclanché cell or similar.

List II (Use/Property/Reaction): Converts energy of combustion into electrical energy: This directly relates to the principle behind fuel cells, which generate electricity through the chemical reaction of a fuel with oxygen.

Does not involve any ion in solution and is used in hearing aids: This refers to the mercury cell, which is chosen for devices requiring a stable voltage, like hearing aids, although the description about ions might be misleading.

The characteristic here is about stable voltage and application in hearing aids.

Rechargeable: This trait is indicative of Ni - Cd cells, which are known for their ability to be recharged multiple times.

Reaction at anode

\mathrm{Zn} \rightarrow \mathrm{Zn}^{2+}+2 \mathrm{e}^{-}

: This anodic reaction is typical in cells like the Leclanché cell, which features a zinc anode undergoing oxidation.

Given these explanations, the correct matches would be: A (Leclanché cell) with IV, due to the anodic reaction involving zinc.

B (Ni - Cd cell) with III, because it is rechargeable.

C (Fuel cell) with I, as it converts the energy of combustion into electrical energy.

D (Mercury cell) with II, by elimination and considering its use in devices like hearing aids and the slight misdescription regarding ions.

Therefore, the correct answer is Option C: A-IV, B-III, C-I, D-II.

Q5

For the redox reaction Zn(s) + Cu2+(0.1 M)

\to

Zn2+(1M) + Cu(s) taking place in a cell,

E_{cell}^o

is 1.10 volt. Ecell for the cell will be (

2.303{{RT} \over F}

= 0.0591)

A 1.80 volt

B 1.07 volt

C 0.82 volt

D 2.14 volt

Correct Answer

Option B

Solution

{E_{cell}} = {E^ \circ }_{cell} + {{0.059} \over n}\log {{\left[ {C{u^{ + 2}}} \right]} \over {\left[ {Z{n^{ + 2}}} \right]}}

= 1.10 + {{0.059} \over 2}\log \left[ {0.1} \right]

= 1.10 - 0.0295

= 1.07V

Q6

The limiting molar conductivities Λ° for NaCl, KBr and KCl are 126, 152 and 150 S cm2 mol-1 respectively. The Λ° for NaBr is

A 128 S cm2 mol-1

B 278 S cm2 mol-1

C 176 S cm2 mol-1

D 302 S cm2 mol-1

Correct Answer

Option A

Solution

{A^ \circ }Nacl = {\lambda ^ \circ }N{a^ + } + \lambda C{l^ - }\,\,\,\,\,\,\,\,\,\,\,...\left( i \right)

{A^ \circ }KBr = {\lambda ^ \circ }{K^ + } + \lambda Br\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,...\left( {ii} \right)

{A^ \circ }KCl = {\lambda ^ \circ }{K^ + } + \lambda C{l^ - }\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,...\left( {iii} \right)

operating

(i)+(ii)-(iii)

{A^ \circ }NaBr = {\lambda ^ \circ }N{a^ + } + {\lambda ^ \circ }B{r^ - }

= 126 + 152 - 150

= 128\,\,\,S\,c{m^2}\,mo{l^{ - 1}}

Q7

In a cell that utilises the reaction Zn(s) + 2H+ (aq)

\to

Zn2+(aq) + H2(g) addition of H2SO4 to cathode compartment, will

A lower the E and shift equilibrium to the left

B increases the E and shift equilibrium to the left

C increase the E and shift equilibrium to the right

D Lower the E and shift equilibrium to the right

Correct Answer

Option C

Solution

Zn\left( s \right) + 2{H^ + } + \left( {aq} \right)\,\,\rightleftharpoons\,\,Z{n^{2 + }}\left( {aq} \right) + {H_2}\left( g \right)

{E_{cell}} = E_{cell}^ \circ - {{0.059} \over 2}\log {{\left[ {Z{n^{2 + }}} \right]\left[ {{H_2}} \right]} \over {{{\left[ {{H^ + }} \right]}^2}}}

Addition of

{H_2}S{O_4}

will increases

\left[ {{H^ + }} \right]

and

{E_{cell}}

will also increase and the equilibrium will shift towards

RHS

Q8

The

E_{{M^{3 + }}/{M^{2 + }}}^o

values for Cr, Mn, Fe and Co are – 0.41, +1.57, + 0.77 and +1.97 V respectively. For which one of these metals the change in oxidation state form +2 to +3 is easiest?

A Fe

B Mn

C Cr

D Co

Correct Answer

Option C

Solution

The given values show that

Cr

has maximum oxidation potential, therefore its oxidation will be easiest. (Change the sign to get the oxidation values)

Q9

Several blocks of magnesium are fixed to the bottom of a ship to :

A make the ship lighter

B prevent action of water and salt

C prevent puncturing by under-sea rocks

D keep away the sharks

Correct Answer

Option B

Solution

Magnesium provides cathodic protection and prevent rusting or corrosion.

Q10

When during electrolysis of a solution of AgNO3, 9650 coulombs of charge pass through the electroplating bath, the mass of silver deposited on the cathode will be :

A 10.8 g

B 21.6 g

C 108 g

D 1.08 g

Correct Answer

Option A

Solution

When

96500

coulomb of electricity is passed through the electroplating bath the amount of Ag deposited

=108g

$\therefore$ when

9650

coulomb of electricity is passed deposited Ag.

\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {{108} \over {96500}} \times 9650 = 10.8\,g