Electrochemistry Test

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Electrochemistry Test - 24

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Question 1
1 / -0

Only One Option Correct Type
This section contains 16 multiple choice questions. Each question has four choices (a), (b), (c) and (d), out of which ONLY ONE is correct
Q.
During the electrolysis of aqueous Zn(NO₃)₂solution

A
Zn plates out at the cathode

B
Zn plates out at the anode

C
H₂ gas is evolved at the anode

D
O₂ gas is evolved at the anode

Solution

In preference to reduction of Zn²⁺ at cathode, O^2- (aq) is oxidised to O₂ at anode.
Question 2
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Schematic diagram of an electrolytic cell is

A

B

C

D
None of these is the correct presentation

Solution

In electrolytic cell,
Cation moves to cathode and anion moves to anode.

Electrons move anode to cathode.
Question 3
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The metal that can not be obtained by electrolysis of an aqueous solution of its salt is
[JEE Main 2014]

A
Ag

B
Ca

C
Cu

D
Cr

Solution

In electro chemical series (ECS),

thus, Ca²⁺ ion is not reduced to C a instead, H₂O is reduce d to H₂.

Ag, Cu and Cr are below H in ECS (E°_reduction > 0), thus they are reduced to metals on electrolysis.

Note In ECS, Ca, H, Cr, Cu elements lying above H are better reducing agents thus are easily oxidised.
Question 4
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When during electrolysis of a solution of AgNO₃ ,9650 C of charge pass through the electroplating bath,the mass of silver deposited on the cathode will be

A
1.08 g

B
10.8 g

C
12.6 g

D
1.8 g

Solution
Question 5
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Refining of impure metal is done by electrolysis using impure metal as anode.Select the correct statement about this refining.

A
E^°_cellof the net reaction is zero

B
metal to be refined is dissolved in the solution and deposited at the cathode.

C
Both (a) and (b)

D
None of the above

Solution

When impure metal (M) is anode and pure metal is made cathode, then

Thus, impure metal from the anode is deposited at the cathode.
Question 6
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W g of Ag is deposited at the cathode of one electrolytic cell due to passage of 1A of current for 1h.Time required for passage of current to deposit W g of Mg by the same value of current is

A
9 h

B
4.5 h

C
1 h

D
3.0 h

Solution
Question 7
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In the refining of silver by electrolytic method, current of 5A is passed for 2 h using 100 g of impure anode of silver (of 95% purity). Weight of silver anode after electrolysis is

A
40.29 g

B
59.71 g

C
57.59 g

D
42.41 g

Solution

By Faraday 's first law of electrolysis
Question 8
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In the electrorefining of metals, impure metal is

A
cathode and oxidation taken place

B
anode and oxidation takes place

C
anode and reduction takes place

D
cathode and reduction takes place

Solution

Impure metal is made the anode and oxidation takes place

Cu²⁺ formed are reduced at cathode and thus, deposited there.
Question 9
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In the electrosynthesis,potassium manganate (VII) is converted to manganese(IV) dioxide. By passage of 1F of electrolysis ,one mole of potassium manganate(VII) will form manganese dioxide.

A
1.00 mol

B
0.50 mol

C
0.66 mol

D
0.33 mol

Solution

Manganate (VII) is MnO₄^- with ON of Mn = + 7
1 mole required 3F of electricity thus, 1 F will reduce only (1/3) mole MnO₄^- t o MnO₂.
Thus, MnO₂ formed = 0.33 mol.
Question 10
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When Al₂O₃ is electrolysed ,cation and anions are discharged. For a given quantity of electricity,ratio of number of moles of Al and O₂ gas is

A
1 : 1

B
2 : 1

C
2 : 3

D
4 : 3

Solution

When same quantity of electricity is passed, elements/gases are formed in the ratio of their equivalents
.
Question 11
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1 Faraday of electricity is passed through the solution containing 1 mole each of AgNO₃, CuSO₄, AlCl₃and SiCl₄. Elements are discharged at the cathode.Number of moles of Ag, Cu,Al and Si formed will be in the ratio of

A
1 : 1 : 1 : 1

B
1 : 2 : 3 : 4

C
6 : 4 : 3 : 1

D
12 : 6 : 4 : 3

Solution

(d)
Question 12
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During electrolysis of acidified water ,O₂ gas is formed at the anode. To produce O₂ gas at the anode at the rate of 0.224 cc per second at STP,current passed is

A
0.224 A

B
2.24 A

C
9.64 A

D
3.86 A

Solution
Question 13
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A solution of copper(II) sulphate (VI) is electrolysed between copper electrodes by a currrent of 10.0 A for exactly 9650 s.Which remains unchanged?

A
Molar concentration of solution

B
Cathodic plate

C
Anodic plate

D
All of these

Solution

0.5 mole of copper is dissolved from the anode. Thus, its mass decreases. 0.5 mole of copper from the anode is deposited at the cathode. Thus, its mass increases.
Thus, molar concentration of aqueous solution of CuSO₄ remains unchanged.
Question 14
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A 300 mL solution of NaCl was electrolysed for 60.0 min. If the pH of the final solution was 12.24,average current used is

A
1.40 A

B
1.27 A

C
0.70 A

D
0.14 A

Solution
Question 15
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100 mL of a buffer of 1 M NH₃(aq) and 1 M NH₄⁺(aq) are placed in two volatic cells separately.A current of 1.5 A is passed through both cells for 20 min. If electrolysis of water only takes place
2H₂O +O₂ + 4e^- → 4OH^- (RHS
2H₂O → 4H^{+. + O₂}+ 4e^- (LHS)
then pH of the

A
LHS half-cell will increase

B
RHS half-cell will increase

C
both half-cell will increase

D
both half-cell will decrease

Solution

In RHS, [NH₃] increases hence, pOH decreases
pH = 14 - pOH
Hence, pH of RHS increases.
In LHS, [NH₄⁺] increases, hence pOH increases and pH decreases.
Question 16
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What product are formed during the electrolysis of a concentrated aqueous solution of sodium chloride using an electrolytic cell in which electrodes are separated by a porous pot?
I. Cl₂(g)
II. NaOH(aq)
III. H₂(g)
IV. NaClO(aq)
V. NaClO₃(aq)
Select the correct choice.

A
I and II

B
I , II and V

C
I , IiI and V

D
I , II and III

Solution

Cl₂(g) is formed at anode and NaOH and H₂ are formed at cathode. Since, cathode and anode are separated. Hence. there is no reaction between the products formed at the cathode and anode.
Note: but these reaction do not occur
Note: NaCl is neutral pH = 7 initially. After electrolysis , NaOH is formed
Hence, solution become, basic pH >7