An aqueous pink solution of cobalt(II) chloride changes to deep blue on addition of excess of HCI. This is because..............

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${[Co {(H_{2} O)}_{6}]}^{2 +}$ is transformed into ${[{CoCl}_{6}]}^{4 -}$

tetrahedral complexes have smaller crystal field splitting than octahedral complexes

${[Co {(H_{2} O)}_{6}]}^{2 +}$ is transformed into ${[{CoCl}_{4}]}^{2 -}$

tetrahedral complexes have larger crystal field splitting than octahedral complex

answer is B, C.

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Detailed Solution

Cobalt (II) chloride's aqueous pink solution is caused by an electron moving from the

${[Co {(H_{2} O)}_{6}]}^{2 -}$ complex's $t_{2_{g}}$ to eg energy state. If too much HCl is added, this solution.

(i) ${[Co {(H_{2} O)}_{6}]}^{2 -}$ is transformed into ${[{CoCl}_{4}]}^{2 -}$ .

(ii) Tetrahedral complexes have smaller crystal field splitting than octahedral complexes because

$Δ r = \frac{4}{9} Δ_{0}$

Hence, options B and C are correct.

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