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Question #44749

Difficulty: 8/10 | 🟢 Free

The Question

An aqueous solution of the coordination compound $\ce{[Co(NH_3)_4Cl_2]Cl}$ is prepared with a molality of $0.1 \text{ m}$ . According to Werner's theory, the primary valency undergoes $100\%$ ionization. However, contrary to the assumption of a perfectly rigid coordination sphere, one of the inner-sphere chloride ligands is labile and establishes the following aquation equilibrium at $298 \text{ K}$ :

$\ce{[Co(NH_3)_4Cl_2]^+ + H_2O(l) <=> [Co(NH_3)_4(H_2O)Cl]^{2+} + Cl^-}$

The equilibrium constant for this aquation reaction is $K_{eq} = 0.15$ (assume molarity $\approx$ molality). Given the ebullioscopic constant of water $K_b = 0.52 \text{ K kg mol}^{-1}$ , what is the observed boiling point elevation ( $\Delta T_b$ ) of the solution?

Options

A.
$0.130 \text{ K}$
B.
$0.104 \text{ K}$
C.
$0.156 \text{ K}$
D.
$0.208 \text{ K}$

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

Degree of Dissociation (Alpha)|Werner’s Theory Postulates|Molecular Mass Abnormalities

Why This Question Is Tricky

Common Mistakes

This problem tests the 'Rigid Coordination Sphere' misconception.

Students typically assume Werner's complexes only dissociate their primary valency, leading to a Van't Hoff factor of i=2 (Option B).

By introducing a labile ligand, the problem forces the calculation of an 'Effective Alpha' for the secondary valency.

Furthermore, it acts as a trap for students who recognize the equilibrium but forget the 'Common Ion Effect' exerted by the primary chloride ion during the ICE table setup.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Electrochemistry - Class 12
Concept	Degree of Dissociation (Alpha)
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free