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Question

When a dilute aqueous solution of lithium chloride is electrolysed using graphite electrodes, which of the following is/are true?


A
both 1 and 2
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B
only 1
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C
only 2
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D
1, 2, 3, 4
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Solution

The correct option is A both 1 and 2
In the given electrolysis method, the electrodes used is graphite.
Graphite is an inert/inactive electrode.
This metal electrode doesn’t involve in the redox reaction of the cell.
Hence, this electrode can conduct electrons into or out of the cell but cannot take part in the half-reactions.
In such cell reactions, no reactants or products are capable of serving as electrodes.

In general, electrolysis of lithium chloride yield the product of Cl2 gas at anode because eventhough the oxidation potential of OH in H2O is higher, the rate of oxidation of water is lower than the rate of production of Cl2.
Thus, to increase the rate of the reaction, an extra potential is applied which is known as overpotential.
Because of this overpotential, oxidation of Cl becomes more feasible.
So,
Anode reaction:
2Cl(aq)Cl2(g)+2e

But in dilute LiCl, the oxidation of Cl does not occurs.
At low concentration of Cl, oxidation of H2O to give O2 is favoured.
Hence, oxygen is liberated at anode.
Anode reaction:
2H2O(l)4H+(aq)+O2(g)+4e

At cathode,
E0Li+/Li=3.04 V
E0H2O/H2=0.83 V

Since, reduction potential of H+ is higher than the reduction potential of Li+. H2O is reduced to give H2 at cathode.
Cathode reaction:
2H2O(l)+2eH2(g)+2OH(aq)

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