Question

An aqueous pink solution of cobalt(II) chloride to deep blue on addition of excess of HCL. This is because ..........
(a) $\left[Co\right(H_{2}O{)}_6{]}^{2+}$ is transformed into $[CoC{l}_6{]}^{4-}$
(b) $\left[Co\right(H_{2}O{)}_6{]}^{2+}$ is transformed into $[CoC{l}_4{]}^{2-}$
(c) tetrahedral complexes have smaller crystal field splitting than octahedral complexes
(d) tetrahedral complexes have larger crystal field splitting than octahedral complex.

Answer 1

Aqueous pink solution of cobalt (II) chloride is due to electronic transition of electron from $t_{2g}$ to $e_g$ energy level of $\left[Co\right(H_{2}O{)}_6{]}^{2+}$ complex. When excess of HCL is added to this solution
(i) $\left[Co\right(H_{2}O{)}_6{]}^{2+}$ is transformed into $[CoC{l}_4{]}^{2-}$.
(ii) tetrahedral complexes have smaller crystal field splitting than octahedral complexes because ${△}_t=\frac{4}{9}{△}_0$
Hence, options (b) and (c) are correct choices.