Q. An aqueous solution of $CoCl_{2}$ on addition of excess of concentrated $HCl$ turns blue to formation of
A) $\left\lbrack CoCl_{4} \right\rbrack^{2 -}$
B) $\left\lbrack Co\left( H_{2}O \right)_{2}Cl_{4} \right\rbrack^{2 -}$
C) $\left\lbrack Co\left( H_{2}O \right)_{2}2Cl_{4} \right\rbrack^{2 -}$
D) $\lbrack Co\left( H_{2}O \right)_{4}Cl_{2}\rbrack$
Explanation
(a)
$CoCl_{2}$ is a weak Lewis acid, reacting with chloride ions to produce salt containing the terrahedral $\left\lbrack CoCl_{4} \right\rbrack^{2 -}$ion. $CoCl_{2}\$is blue when anhydrous, and a deep magenta colour when hydrated, for this reason it is widely used as an indicator for water
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.