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Question

Which of the following does not evolve oxygen at anode when electroysis is carried?

Given:
E0Cu/Cu2+=0.34 V
E0H2O/O2=1.23 V

A
dil.H2SO4 with Pt electrode
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B
Fused NaOH with Pt electrode
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C
Acidic water with Pt electrode
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D
dil.H2SO4 with Cu electrode
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Solution

The correct option is D dil.H2SO4 with Cu electrode
In (a), (b) and (c) Pt electrode is used. It is an inert electrode.
Inert electrode are metal electrode in which, metal doesn’t involve in the redox reaction of the cell.
Eg. Pt and graphite electrodes.
Here, electrode materials 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.
The species involved in the half reactions cannot act as electrodes.

In option (d), copper electrode is used. It is an active electrode.
Active electrode is a metal electrodes in which metals themselves are components of the half reactions.
Eg. Cu, Zn, Ag, Hg, etc.,
In Daniell cell, active electrodes are used. Zinc rod at anodic half cell and copper rod at cathodic half cells are active electrodes.

For electrolysis of dil.H2SO4 with copper electrode,
E0Cu/Cu2+=0.34 V
E0H2O/O2=1.23 V
Comparing the oxidation potential, Cu has higher tendency to get oxidised compared to OH(aq)

In the electrolysis of dil. H2SO4 using Cu electrodes, the reaction at anode occurs is
Cu(s)Cu2+(aq)+2e
Here, the copper electrode is not inert and so participates in the reaction.

In all other reaction, inert electrode i.e. Pt is used. Thus, OH/H2O migrate toward the anode and gets oxidised to evolve oxygen.
2H2O(l)4H+(aq)+O2(g)+4e
E0H2O/O2=1.23 V

Thus, option (c) is correct.

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