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Question #44735

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The Question

An aqueous solution of $\ce{Pd(NO3)2}$ is treated with excess $\ce{KSCN}$ to form a thermodynamically stable square planar complex ion, $P$ . The ligand in $P$ exhibits linkage isomerism but coordinates predominantly through its softer donor atom. The overall formation constant ( $\beta_4$ ) of $P$ is $10^{24}$ .

A half-cell is constructed by dipping a Palladium rod into a $1.0\text{ L}$ solution initially containing $0.1\text{ M } \ce{Pd^{2+}}$ and $0.5\text{ M } \ce{SCN^-}$ at $298\text{ K}$ .

Given: $E^\circ_{\ce{Pd^{2+}/Pd}} = +0.95\text{ V}$ , $\frac{2.303RT}{F} = 0.06\text{ V}$ .

Identify the correct IUPAC name of the complex ion $P$ and the reduction potential ( $E_{\text{red}}$ ) of this half-cell.

Options

A.
tetrathiocyanato- $\kappa S$ -palladate(II) ion; $+0.32\text{ V}$
B.
tetrathiocyanato- $\kappa N$ -palladate(II) ion; $+0.23\text{ V}$
C.
tetrathiocyanato- $\kappa S$ -palladate(II) ion; $+0.92\text{ V}$
D.
tetrathiocyanato- $\kappa N$ -palladate(II) ion; $+0.32\text{ V}$

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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

Nernst Equation Concentration Dependence|Werner’s Theory Postulates|Ambidentate Linkage Isomerism

Why This Question Is Tricky

Common Mistakes

This problem integrates Coordination Chemistry (HSAB theory and linkage isomerism) with Electrochemistry (Nernst equation coupled to complexation equilibria).

The 'Hidden Variable' is the drastic reduction in free metal ion concentration due to the high formation constant ( $\beta_4$ ).

Students often fall into three traps: 1) Failing to identify $\ce{Pd^{2+}}$ as a soft acid, leading to the incorrect $\kappa N$ isomer. 2) Forgetting to subtract the stoichiometrically consumed ligand from the initial concentration, which skews the free $[\ce{SCN^-}]$ and subsequently the free $[\ce{Pd^{2+}}]$ . 3) Confusing the non-standard half-cell potential ( $E_{\text{cell}}$ ) with the standard reduction potential of the complex ( $E^\circ_{\text{complex}} = +0.23\text{ V}$ ).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Electrochemistry - Class 12
Concept	Nernst Equation Concentration Dependence
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free