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Electrochemistry question

2007 · Shift 0 · Q27
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  5. /2007 · Shift 0 · Q27

Electrochemistry question

2007 · Shift 0 · Q27

JEE MainChemistryElectrochemistryMCQ+4 / −1
The cell, ZnZnZn | Zn2+Zn^{2+}Zn2+ (1M) || Cu2+Cu^{2+}Cu2+ (1M) | CuCuCu(EcelloE_{cell}^oEcello​= 1.10V) was allowed to be completely discharged at 298 K. The relative concentration of Zn2+Zn^{2+}Zn2+ to Cu2+Cu^{2+}Cu2+[[Zn2+][Cu2+]]\left[ {{{\left[ {Z{n^{2 + }}} \right]} \over {\left[ {C{u^{2 + }}} \right]}}} \right][[Cu2+][Zn2+]​]$ is
  1. A
    antilog (24.08)
  2. B
    37.3
  3. C
    1037.3
  4. D
    9.65 ×\times× 104
View written solutionFree

Correct answer: C

  1. Write the cell reaction

For the Daniell cell:

Zn∣Zn2+(1M)∣∣Cu2+(1M)∣CuZn|Zn^{2+}(1M)||Cu^{2+}(1M)|CuZn∣Zn2+(1M)∣∣Cu2+(1M)∣Cu

The overall reaction is:

Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s)Zn(s)+Cu^{2+}(aq) \rightarrow Zn^{2+}(aq)+Cu(s)Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s)

Here, number of electrons transferred is

n=2n=2n=2


  1. Condition for complete discharge

When the cell is completely discharged, it can no longer produce emf, so:

Ecell=0E_{cell}=0Ecell​=0

Use the Nernst equation:

Ecell=Ecell∘−0.0591nlog⁡QE_{cell}=E^\circ_{cell}-\frac{0.0591}{n}\log QEcell​=Ecell∘​−n0.0591​logQ

At 298 K298\,K298K and for this reaction,

Q=[Zn2+][Cu2+]Q=\frac{[Zn^{2+}]}{[Cu^{2+}]}Q=[Cu2+][Zn2+]​

So at complete discharge:

0=1.10-\frac{0.0591}{2}\log\left(\frac{[Zn^{2+}]}{[Cu^{2+}]}}\right)

Thus,

\frac{0.0591}{2}\log\left(\frac{[Zn^{2+}]}{[Cu^{2+}]}}\right)=1.10

\log\left(\frac{[Zn^{2+}]}{[Cu^{2+}]}}\right)=\frac{2\times 1.10}{0.0591}

\log\left(\frac{[Zn^{2+}]}{[Cu^{2+}]}}\right)\approx 37.3

Therefore,

\frac{[Zn^{2+}]}{[Cu^{2+}]}}=\text{antilog}(37.3)=10^{37.3}


  1. Match with options

Option C is written as 1037.310^{37.3}1037.3 (the formatting in the options seems compressed as 1037.3).

So the correct option is:

C\boxed{C}C​


  1. Comparison with stored correct answer

Stored correct answer: C

Derived answer: C

They agree.

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