Question

Addition of a few drops of concentrated HCl to an aqueous solution of CoCl₂ forms a dark blue complex X.
The CORRECT statement(s) for this reaction is(are):
(Given: Atomic number of Co: 27)
 

• A. X is a centrosymmetric complex.
• B. The oxidation state of cobalt does not change in this reaction.
• C. The number of unpaired electrons on cobalt in X and in (\( {CoCl}_2 \)) (aqueous solution) are the same.
• D. The spin only magnetic moment value for X is 3.87 BM.

Hint:

The magnetic moment of a complex can be estimated using the spin-only formula, which depends on the number of unpaired electrons. For \( {Co}^{2+} \), with 3 unpaired electrons, the magnetic moment is 3.87 BM.

Answer 1

The Correct Option is B, C, D

In this reaction, cobalt(II) chloride (\( {CoCl}_2 \)) reacts with HCl, forming a dark blue complex. The cobalt ion in the complex is in the \( +2 \) oxidation state, which remains unchanged throughout the reaction. Therefore, statement (B) is correct, as the oxidation state of cobalt does not change in this process.
Regarding the number of unpaired electrons, cobalt(II) in both the complex and the aqueous solution has the same electronic configuration, resulting in the same number of unpaired electrons in both species. Hence, statement (C) is also correct.
The spin-only magnetic moment is a measure of the unpaired electrons in a complex. For \( {Co}^{2+} \) in an octahedral complex with 3 unpaired electrons, the magnetic moment can be calculated using the formula: \[ \mu_{{sp}} = \sqrt{n(n+2)} \, {BM} \] where \( n \) is the number of unpaired electrons. With 3 unpaired electrons, the magnetic moment is approximately 3.87 BM, which confirms that statement (D) is correct. Thus, the correct answers are (B), (C), and (D).