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Electrochemistry question

2006 · Shift 0 · Q7
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Electrochemistry question

2006 · Shift 0 · Q7

JEE MainChemistryElectrochemistryMCQ+4 / −1
Given the data at 25oC, AgAgAg + I−I^-I− →\to→ AgIAgIAgI + e- , Eo = 0.152 V AgAgAg →\to→ Ag+Ag^+Ag+ + e-, Eo = -0.800 V What is the value of log Ksp for AgIAgIAgI? (2.303 RT/F = 0.059 V)
  1. A
    –8.12
  2. B
    +8.612
  3. C
    –37.83
  4. D
    –16.13
View written solutionFree

Correct answer: D

  1. Write the given half-reactions

We are given:

(i)Ag+I−→AgI+e−E∘=0.152 V\text{(i)}\quad Ag + I^- \rightarrow AgI + e^- \qquad E^\circ = 0.152\,V(i)Ag+I−→AgI+e−E∘=0.152V

(ii)Ag→Ag++e−E∘=−0.800 V\text{(ii)}\quad Ag \rightarrow Ag^+ + e^- \qquad E^\circ = -0.800\,V(ii)Ag→Ag++e−E∘=−0.800V

We need to find log⁡Ksp\log K_{sp}logKsp​ for:

AgI(s)⇌Ag++I−AgI(s) \rightleftharpoons Ag^+ + I^-AgI(s)⇌Ag++I−

  1. Obtain the reaction for formation of AgIAgIAgI from Ag+Ag^+Ag+ and I−I^-I−

Reverse reaction (ii):

Ag++e−→AgE∘=+0.800 VAg^+ + e^- \rightarrow Ag \qquad E^\circ = +0.800\,VAg++e−→AgE∘=+0.800V

Now add it to reaction (i):

Ag+I−→AgI+e−Ag + I^- \rightarrow AgI + e^-Ag+I−→AgI+e− Ag++e−→AgAg^+ + e^- \rightarrow AgAg++e−→Ag

On adding, AgAgAg and e−e^-e− cancel:

Ag++I−→AgIAg^+ + I^- \rightarrow AgIAg++I−→AgI

For this reaction,

E∘=0.152+0.800=0.952 VE^\circ = 0.152 + 0.800 = 0.952\,VE∘=0.152+0.800=0.952V

  1. Relate E∘E^\circE∘ to equilibrium constant

For the reaction

Ag++I−→AgIAg^+ + I^- \rightarrow AgIAg++I−→AgI

number of electrons transferred is n=1n=1n=1.

Using

E∘=0.059nlog⁡KE^\circ = \frac{0.059}{n} \log KE∘=n0.059​logK

we get

0.952=0.059log⁡K0.952 = 0.059 \log K0.952=0.059logK

So,

log⁡K=0.9520.059≈16.13\log K = \frac{0.952}{0.059} \approx 16.13logK=0.0590.952​≈16.13

Here KKK is the equilibrium constant for:

Ag++I−→AgIAg^+ + I^- \rightarrow AgIAg++I−→AgI

But

K=1KspK = \frac{1}{K_{sp}}K=Ksp​1​

because

AgI⇌Ag++I−AgI \rightleftharpoons Ag^+ + I^-AgI⇌Ag++I−

has equilibrium constant KspK_{sp}Ksp​.

Therefore,

log⁡Ksp=−log⁡K=−16.13\log K_{sp} = -\log K = -16.13logKsp​=−logK=−16.13

  1. Final answer

log⁡Ksp=−16.13\boxed{\log K_{sp} = -16.13}logKsp​=−16.13​

So the correct option is D.

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