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Question #45034

Difficulty: 8/10 | 🟢 Free

The Question

A coordination compound $X$ with the empirical formula \ce{CoI(NO3)2 * 5NH3} is kinetically inert in aqueous solution at 298 K and yields no precipitate upon treatment with cold aqueous \ce{AgNO3}.

When $X$ is dissolved in anhydrous acetonitrile and heated to 350 K, it undergoes a spontaneous inner-sphere electron transfer (ISET), evolving a violet vapor. The resulting transition metal species is then treated with an excess of \ce{[(C2H5)4N]Cl}, forming a thermodynamically stable, kinetically labile complex $Y$ .

According to Werner's theory and Crystal Field Theory, what is the change in the Primary Valency ( $\Delta PV$ ) and Secondary Valency ( $\Delta SV$ ) of the cobalt center from $X$ to $Y$ , and what is the spin-only magnetic moment ( $\mu_{spin}$ ) of complex $Y$ ?

Options

A.
$\Delta PV = -1$ , $\Delta SV = -2$ , $\mu_{spin} = \sqrt{15}$ BM
B.
$\Delta PV = 0$ , $\Delta SV = -2$ , $\mu_{spin} = \sqrt{24}$ BM
C.
$\Delta PV = -1$ , $\Delta SV = 0$ , $\mu_{spin} = \sqrt{15}$ BM
D.
$\Delta PV = 0$ , $\Delta SV = 0$ , $\mu_{spin} = 0$ BM

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Complex Ion Oxidation States|Werner’s Theory Postulates

Why This Question Is Tricky

Common Mistakes

This question tests the boundary between Werner's static postulates and dynamic redox chemistry.

Students often rigidly apply Werner's theory, assuming the primary valency (oxidation state) is immutable during ligand exchange (Trap D).

The hidden variable is the inner-sphere electron transfer (ISET) triggered by the non-aqueous solvent and heat, where the iodide ligand acts as an internal reductant, shifting the metal from a kinetically inert Co(III) to a labile Co(II) state.

Furthermore, it tests the structural knowledge that Co(II) with excess chloride in non-aqueous media strongly favors a tetrahedral geometry, altering the secondary valency.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Redox Reactions - Class 11 Part 2
Concept	Complex Ion Oxidation States
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free