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JEE Chemistry 2023 Question with Solution

The reaction 12H2(g)+AgCl(s)⇋H+(aq)+Cl−(aq)+Ag(s)\frac{1}{2} H_2(g) + AgCl(s) \leftrightharpoons H^+(aq) + Cl^-(aq) + Ag(s) occurs in which of the given galvanic cells?

  • A

    Pt ∣\vert H2_2(g) ∣\vert HCl(soln^n) ∣\vert AgNO3_3(soln^n) ∣\vert Ag

  • B

    Pt ∣\vert H2_2(g) ∣\vert HCl(soln^n) ∣\vert AgCl(s) ∣\vert Ag

  • C

    Pt ∣\vert H2_2(g) ∣\vert KCl(soln^n) ∣\vert AgCl(s) ∣\vert Ag

  • D

    Ag ∣\vert AgCl(s) ∣\vert KCl(soln^n) ∣\vert AgNO3_3 ∣\vert Ag

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: The overall reaction is

12H2(g)+AgCl(s)⇋H+(aq)+Cl−(aq)+Ag(s)\frac{1}{2} H_2(g) + AgCl(s) \leftrightharpoons H^+(aq) + Cl^-(aq) + Ag(s)

Find: Which galvanic cell corresponds to this reaction.

The reaction involves oxidation of hydrogen gas and reduction of silver chloride.

The electrode reactions are:

H2→2H++2e−H_2 \to 2H^+ + 2e^-

and

AgCl+e−→Ag+Cl−AgCl + e^- \to Ag + Cl^-

So, one half-cell must be the hydrogen electrode, which requires H2(g)H_2(g) and a solution containing H+H^+ ions. The other half-cell must be the AgCl(s)/AgAgCl(s)/Ag electrode.

The cell setup matching these two half-cells is

Pt∣H2(g)∣HCl(soln)∣AgCl(s)∣Ag\text{Pt} \vert \text{H}_2(\text{g}) \vert \text{HCl(sol}^n\text{)} \vert \text{AgCl(s)} \vert \text{Ag}

Here, HCl provides the H+H^+ ions needed for the hydrogen electrode, and AgCl(s)AgCl(s) is reduced to AgAg with formation of Cl−Cl^-.

Therefore, the correct option is B.

Matching the Half-Cells

Given: The net reaction contains H2H_2, H+H^+, AgClAgCl, Cl−Cl^-, and AgAg. Find: The galvanic cell whose electrodes and electrolyte reproduce this reaction.

From the products, hydrogen is being oxidized:

12H2→H++e−\frac{1}{2}H_2 \to H^+ + e^-

So the anode must be a hydrogen electrode using inert platinum and an acidic medium.

Also, silver chloride is being reduced:

AgCl+e−→Ag+Cl−AgCl + e^- \to Ag + Cl^-

So the cathode must be an AgCl(s)/AgAgCl(s) / Ag electrode.

Among the options, only option B contains both required parts together: a platinum hydrogen electrode in HCl solution and a silver-silver chloride electrode.

Hence, the cell representing the given reaction is option B.

Common mistakes

  • Choosing the cell with AgNO3AgNO_3 because it contains silver. This is wrong because the reaction requires reduction of AgCl(s)AgCl(s), not Ag+Ag^+ from silver nitrate. Look for the AgCl(s)/AgAgCl(s)/Ag electrode specifically.

  • Ignoring the need for H+H^+ ions at the hydrogen electrode. This is wrong because oxidation of H2H_2 produces H+H^+, so the medium must support the hydrogen half-cell. Use the option containing HCl for this half-cell.

  • Confusing the direction of oxidation and reduction. This is wrong because H2H_2 is oxidized while AgClAgCl is reduced in the given reaction. First split the net reaction into half-reactions before matching the cell.

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