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Electrochemistry question

2021 · 26 Feb · Shift 2 · Q21
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Electrochemistry question

2021 · 26 Feb · Shift 2 · Q21

JEE MainChemistryElectrochemistryNumerical+4 / −1
Emf of the following cell at 298K in V is x ×\times× 10 −-− 2. ZnZnZn|Zn2+Zn^{2+}Zn2+(0.1 M)||Ag+Ag^+Ag+ (0.01 M)|AgAgAg The value of x is ‾\underline{\hspace{2cm}}​. (Rounded off to the nearest integer) [Given : EZn2+/Znθ=−0.76V;EAg2+/Agθ=+0.80V;2.303RTF=0.059E_{Z{n^{2 + }}/Zn}^\theta = - 0.76V;E_{A{g^{2 + }}/Ag}^\theta = + 0.80V;{{2.303RT} \over F} = 0.059EZn2+/Znθ​=−0.76V;EAg2+/Agθ​=+0.80V;F2.303RT​=0.059]
Numerical answer
View written solutionFree

Correct answer: 147

  1. Write the cell reaction

Given cell: Zn∣Zn2+(0.1 M)∣∣Ag+(0.01 M)∣Ag\text{Zn}|\text{Zn}^{2+}(0.1\,M)||\text{Ag}^+(0.01\,M)|\text{Ag}Zn∣Zn2+(0.1M)∣∣Ag+(0.01M)∣Ag

At anode: Zn→Zn2++2e−\text{Zn} \rightarrow \text{Zn}^{2+}+2e^-Zn→Zn2++2e−

At cathode: Ag++e−→Ag\text{Ag}^+ + e^- \rightarrow \text{Ag}Ag++e−→Ag

Balancing electrons: 2Ag++2e−→2Ag2\text{Ag}^+ + 2e^- \rightarrow 2\text{Ag}2Ag++2e−→2Ag

Overall reaction: Zn+2Ag+→Zn2++2Ag\text{Zn} + 2\text{Ag}^+ \rightarrow \text{Zn}^{2+} + 2\text{Ag}Zn+2Ag+→Zn2++2Ag

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

  1. Calculate standard emf of the cell

Ecell∘=Ecathode∘−Eanode∘E^\circ_{\text{cell}}=E^\circ_{\text{cathode}}-E^\circ_{\text{anode}}Ecell∘​=Ecathode∘​−Eanode∘​

Ecell∘=0.80−(−0.76)=1.56 VE^\circ_{\text{cell}}=0.80-(-0.76)=1.56\,VEcell∘​=0.80−(−0.76)=1.56V

  1. Write the reaction quotient

For the overall reaction, Q=[Zn2+][Ag+]2Q=\frac{[\text{Zn}^{2+}]}{[\text{Ag}^+]^2}Q=[Ag+]2[Zn2+]​

Given: [Zn2+]=0.1,[Ag+]=0.01[\text{Zn}^{2+}]=0.1,\qquad [\text{Ag}^+]=0.01[Zn2+]=0.1,[Ag+]=0.01

Hence, Q=0.1(0.01)2=0.110−4=1000Q=\frac{0.1}{(0.01)^2}=\frac{0.1}{10^{-4}}=1000Q=(0.01)20.1​=10−40.1​=1000

  1. Apply Nernst equation at 298 K

Ecell=Ecell∘−0.059nlog⁡QE_{\text{cell}}=E^\circ_{\text{cell}}-\frac{0.059}{n}\log QEcell​=Ecell∘​−n0.059​logQ

Substitute values: Ecell=1.56−0.0592log⁡(1000)E_{\text{cell}}=1.56-\frac{0.059}{2}\log(1000)Ecell​=1.56−20.059​log(1000)

Since, log⁡(1000)=3\log(1000)=3log(1000)=3

So, Ecell=1.56−0.0592×3E_{\text{cell}}=1.56-\frac{0.059}{2}\times 3Ecell​=1.56−20.059​×3

Ecell=1.56−0.0885=1.4715 VE_{\text{cell}}=1.56-0.0885=1.4715\,VEcell​=1.56−0.0885=1.4715V

  1. Express in the form x×10−2x \times 10^{-2}x×10−2 V

1.4715 V=147.15×10−2 V1.4715\,V = 147.15 \times 10^{-2}\,V1.4715V=147.15×10−2V

Rounded to nearest integer, x=147x=147x=147

Hence, the required answer is: 147\boxed{147}147​

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