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Question #45021

Difficulty: 8/10 | 🟢 Free

The Question

Consider the following electrochemical cell at $298 \text{ K}$ :

$\ce{Zn(s) | [Zn(NH_3)_4]^{2+}(aq, 0.10 M), NH_3(aq, 1.0 M) || OH^{-}(aq, 0.10 M) | Zn(OH)_2(s) | Zn(s)}$

Given the following thermodynamic data: $K_f(\ce{[Zn(NH_3)_4]^{2+}}) = 1.0 \times 10^9$ $K_{sp}(\ce{Zn(OH)_2}) = 1.0 \times 10^{-15}$ $E^\circ_{\ce{Zn^{2+}/Zn}} = -0.76 \text{ V}$ $\frac{2.303 RT}{F} = 0.06 \text{ V}$

Determine the initial cell potential ( $E_{\text{cell}}$ ) and the spontaneous direction of electron flow in the external circuit.

Options

A.
$-0.09 \text{ V}$ , Right to Left
B.
$+0.09 \text{ V}$ , Left to Right
C.
$-0.12 \text{ V}$ , Right to Left
D.
$-0.85 \text{ V}$ , Right to Left

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Electrode Potential Sign Conventions|Metal Activity Series Logic|Concentration Cells

Why This Question Is Tricky

Common Mistakes

This question tests the thermodynamic principles of concentration cells and the Nernst equation.

The primary trap is the 'Hidden Variable' of $E^\circ_{\text{cell}}$ : students often erroneously substitute the highly negative standard reduction potential of the active metal ( $-0.76 \text{ V}$ ) into the Nernst equation instead of $0 \text{ V}$ , leading to Distractor D.

Additionally, it tests the 'Chemical Exception' where a cell diagram is written such that the cathodic concentration is lower than the anodic concentration, resulting in a negative $E_{\text{cell}}$ .

Students must recognize that a negative potential implies the spontaneous electron flow is opposite to the standard left-to-right convention.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Redox Reactions - Class 11 Part 2
Concept	Electrode Potential Sign Conventions
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free