JEE Main · 2019 · Shift-ImediumEC-086

Consider the following reduction pro: {Zn^{2+} + 2e^- Zn(s)}; E° = -0.76\ {V} {Ca^{2+} + 2e^- Ca(s)}; E° = -2.87\ {V}…

Electrochemistry · Class 12 · JEE Main Previous Year Question

Question

Consider the following reduction pro\cesses: Zn2++2e−→Zn(s);E°=−0.76 V\mathrm{Zn^{2+} + 2e^- \rightarrow Zn(s)};\quad E° = -0.76\ \mathrm{V} Ca2++2e−→Ca(s);E°=−2.87 V\mathrm{Ca^{2+} + 2e^- \rightarrow Ca(s)};\quad E° = -2.87\ \mathrm{V} Mg2++2e−→Mg(s);E°=−2.36 V\mathrm{Mg^{2+} + 2e^- \rightarrow Mg(s)};\quad E° = -2.36\ \mathrm{V} Ni2++2e−→Ni(s);E°=−0.25 V\mathrm{Ni^{2+} + 2e^- \rightarrow Ni(s)};\quad E° = -0.25\ \mathrm{V}

The reducing power of the metals increases in the order:

Options
  1. a

    Ca<Mg<Zn<Ni\mathrm{Ca < Mg < Zn < Ni}

  2. b

    Zn<Mg<Ni<Ca\mathrm{Zn < Mg < Ni < Ca}

  3. c

    Ni<Zn<Mg<Ca\mathrm{Ni < Zn < Mg < Ca}

    ✓
  4. d

    Ca<Zn<Ni<Mg\mathrm{Ca < Zn < Ni < Mg}

Correct Answerc

Ni<Zn<Mg<Ca\mathrm{Ni < Zn < Mg < Ca}

Detailed Solution

Strategy: Reducing power refers to the ability to oxidize yourself (act as a reducing agent). A species with a more negative standard reduction potential (E∘E^\circ) is more easily oxidized and thus is a stronger reducing agent.

Rank by Reduction Potentials:

  1. Ca: −2.87 V-2.87 \text{ V} (Most negative)
  2. Mg: −2.36 V-2.36 \text{ V}
  3. Zn: −0.76 V-0.76 \text{ V}
  4. Ni: −0.25 V-0.25 \text{ V} (Least negative)

Order of Increasing Reducing Power: Sin\ce more negative means more powerful: Ni < Zn < Mg < Ca

Answer: (c) Ni < Zn < Mg < Ca\boxed{\text{Answer: (c) Ni < Zn < Mg < Ca}}

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