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Question #44327

Difficulty: 8/10 | 🟢 Free

The Question

An aqueous solution of $\ce{CoCl2}$ is oxidized by atmospheric oxygen in the presence of ethylenediamine ( $en$ ) and $\ce{HCl}$ at 298 K, yielding the kinetically inert octahedral complex cation $\ce{[Co(en)2Cl2]+}$ . The stabilization of the central metal's oxidation state is strictly governed by Crystal Field Stabilization Energy (CFSE) rather than simple VSEPR expectations. Determine the primary valency of the metal (per Werner's Theory), the CFSE of the complex (in terms of $\Delta_o$ , ignoring pairing energy), and the total number of stereoisomers exhibited by this complex cation.

Options

A.
3, -2.4 $\Delta_o$ , 3
B.
3, -0.4 $\Delta_o$ , 2
C.
2, -1.8 $\Delta_o$ , 3
D.
3, -2.4 $\Delta_o$ , 2

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

d-block Variable Oxidation States|Werner’s Theory Postulates|Geometric Isomerism Requirements

Why This Question Is Tricky

Common Mistakes

This question tests the intersection of Werner's Theory, Crystal Field Theory, and Coordination Stereochemistry.

The 'Hidden Variable' is the thermodynamic driving force: students often fail to recognize that Co(II) oxidizes to Co(III) specifically because the massive CFSE of a low-spin $d^6$ complex (-2.4 $\Delta_o$ ) overcomes the ionization energy.

The 'Chemical Exception/Trap' lies in the stereochemistry: students frequently miscount the stereoisomers of an $\ce{[M(AA)2B2]}$ complex as 2 (just cis and trans), forgetting that the cis isomer is chiral and must be resolved into a pair of enantiomers, making the true total 3.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Classification of Elements and Periodicity in Properties - Class 11 Part 1
Concept	d-block Variable Oxidation States
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free