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Electrochemistry question

2021 · 22 Jul · Shift 2 · Q18
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Electrochemistry question

2021 · 22 Jul · Shift 2 · Q18

JEE MainChemistryElectrochemistryNumerical+4 / −1
Assume a cell with the following reaction Cu(s)+2Ag+(1×10−3M)→Cu2+(0.250M)+2Ag(s)C{u_{(s)}} + 2A{g^ + }(1 \times {10^{ - 3}}M) \to C{u^{2 + }}(0.250M) + 2A{g_{(s)}}Cu(s)​+2Ag+(1×10−3M)→Cu2+(0.250M)+2Ag(s)​ EcellΘ=2.97E_{cell}^\Theta = 2.97EcellΘ​=2.97 V Ecell for the above reaction is ‾\underline{\hspace{2cm}}​ V. (Nearest integer) [Given : log 2.5 = 0.3979, T = 298 K]
Numerical answer
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Correct answer: 3

  1. Write the cell reaction and identify nnn

Given reaction: Cu(s)+2Ag+(10−3M)→Cu2+(0.250M)+2Ag(s)Cu_{(s)} + 2Ag^+(10^{-3}M) \to Cu^{2+}(0.250M) + 2Ag_{(s)}Cu(s)​+2Ag+(10−3M)→Cu2+(0.250M)+2Ag(s)​

Here, copper is oxidized: Cu→Cu2++2e−Cu \to Cu^{2+} + 2e^-Cu→Cu2++2e−

Silver ion is reduced: 2Ag++2e−→2Ag2Ag^+ + 2e^- \to 2Ag2Ag++2e−→2Ag

So, the number of electrons transferred is: n=2n=2n=2

  1. Use the Nernst equation

For the reaction, Ecell=Ecell∘−0.0591nlog⁡QE_{cell} = E_{cell}^\circ - \frac{0.0591}{n}\log QEcell​=Ecell∘​−n0.0591​logQ

At 298 K298\,K298K, with n=2n=2n=2: Ecell=2.97−0.05912log⁡QE_{cell} = 2.97 - \frac{0.0591}{2}\log QEcell​=2.97−20.0591​logQ

  1. Calculate the reaction quotient QQQ

For Cu(s)+2Ag+→Cu2++2Ag(s)Cu_{(s)} + 2Ag^+ \to Cu^{2+} + 2Ag_{(s)}Cu(s)​+2Ag+→Cu2++2Ag(s)​

Solids are omitted, so Q=[Cu2+][Ag+]2Q = \frac{[Cu^{2+}]}{[Ag^+]^2}Q=[Ag+]2[Cu2+]​

Substitute the given concentrations: Q=0.250(10−3)2=0.250×106=2.5×105Q = \frac{0.250}{(10^{-3})^2} = 0.250 \times 10^6 = 2.5 \times 10^5Q=(10−3)20.250​=0.250×106=2.5×105

  1. Evaluate log⁡Q\log QlogQ

log⁡(2.5×105)=log⁡2.5+5=0.3979+5=5.3979\log(2.5 \times 10^5) = \log 2.5 + 5 = 0.3979 + 5 = 5.3979log(2.5×105)=log2.5+5=0.3979+5=5.3979

  1. Substitute into Nernst equation

Ecell=2.97−0.05912(5.3979)E_{cell} = 2.97 - \frac{0.0591}{2}(5.3979)Ecell​=2.97−20.0591​(5.3979)

0.05912=0.02955\frac{0.0591}{2} = 0.0295520.0591​=0.02955

So, Ecell=2.97−0.02955×5.3979E_{cell} = 2.97 - 0.02955 \times 5.3979Ecell​=2.97−0.02955×5.3979

0.02955×5.3979≈0.15950.02955 \times 5.3979 \approx 0.15950.02955×5.3979≈0.1595

Thus, Ecell≈2.97−0.1595=2.8105 VE_{cell} \approx 2.97 - 0.1595 = 2.8105\,VEcell​≈2.97−0.1595=2.8105V

  1. Nearest integer

Ecell≈3 VE_{cell} \approx 3\,VEcell​≈3V

Therefore, the required nearest integer is 3.

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