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Electrochemistry question

2017 · Shift 2 · Q17
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Electrochemistry question

2017 · Shift 2 · Q17

JEE AdvancedChemistryElectrochemistryMCQ+3 / −0.75
For the following cell, Zn(s)∣ZnSO4(aq)∣∣CuSO4(aq)∣Cu(s)Zn\left( s \right)\left| {ZnS{O_4}\left( {aq} \right)} \right|\left| {CuS{O_4}\left( {aq} \right)} \right|Cu\left( s \right)Zn(s)∣ZnSO4​(aq)∣∣CuSO4​(aq)∣Cu(s) when the concentration of Zn2+Z{n^{2 + }}Zn2+ is 101010 times the concentration of Cu2+,C{u^{2 + }},Cu2+, the expression for ΔG\Delta GΔG(in J mol−1J\,mo{l^{ - 1}}Jmol−1) is [FFF is Faraday constant; RRR is gas constant; TTT is temperature; E0{E^0}E0 (cell) =1.1V=1.1V=1.1V]
  1. A
    1.1F1.1F1.1F
  2. B
    2.303RT−2.2F2.303RT-2.2F2.303RT−2.2F
  3. C
    2.303RT+1.1F2.303RT+1.1F2.303RT+1.1F
  4. D
    −2.2F-2.2F−2.2F
View written solutionFree

Correct answer: B

  1. Cell reaction

For the cell Zn(s) ∣ ZnSO4(aq) ∣∣ CuSO4(aq) ∣ Cu(s)Zn(s)\,|\,ZnSO_4(aq)\,||\,CuSO_4(aq)\,|\,Cu(s)Zn(s)∣ZnSO4​(aq)∣∣CuSO4​(aq)∣Cu(s)

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: n=2n=2n=2

  1. Reaction quotient

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

Given: [Zn2+]=10[Cu2+][Zn^{2+}] = 10[Cu^{2+}][Zn2+]=10[Cu2+] So, Q=10Q=10Q=10

  1. Use Nernst equation

At general temperature TTT, E=E∘−RTnFln⁡QE=E^\circ-\frac{RT}{nF}\ln QE=E∘−nFRT​lnQ

Substitute E∘=1.1 VE^\circ=1.1\,VE∘=1.1V, n=2n=2n=2, and Q=10Q=10Q=10: E=1.1−RT2Fln⁡10E=1.1-\frac{RT}{2F}\ln 10E=1.1−2FRT​ln10

Since ln⁡10=2.303\ln 10 = 2.303ln10=2.303 we get E=1.1−2.303RT2FE=1.1-\frac{2.303RT}{2F}E=1.1−2F2.303RT​

  1. Relate ΔG\Delta GΔG and cell emf

We use: ΔG=−nFE\Delta G=-nFEΔG=−nFE

So, ΔG=−2F(1.1−2.303RT2F)\Delta G=-2F\left(1.1-\frac{2.303RT}{2F}\right)ΔG=−2F(1.1−2F2.303RT​)

Now simplify: ΔG=−2.2F+2.303RT\Delta G=-2.2F+2.303RTΔG=−2.2F+2.303RT

Thus, ΔG=2.303RT−2.2F\boxed{\Delta G=2.303RT-2.2F}ΔG=2.303RT−2.2F​

  1. Option check
  • A: 1.1F1.1F1.1F ❌
  • B: 2.303RT−2.2F2.303RT-2.2F2.303RT−2.2F ✅
  • C: 2.303RT+1.1F2.303RT+1.1F2.303RT+1.1F ❌
  • D: −2.2F-2.2F−2.2F ❌

Hence the correct option is B.

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