Question

An aqueous solution of $CoC{l}_2$ on addition of excess of concentrated $HCl$ turn blue due to formation of:

• A. $\left[Co\right(H_{2}O{)}_{4}C{l}_2]$
• B. $\left[Co\right(H_{2}O{)}_{2}Cl{]}^{2-}$
• C. $[CoC{l}_4{]}^{2-}$
• D. $\left[Co\right(H_{2}O{)}_{2}C{l}_2]$

Answer 1

The correct option is C $[CoC{l}_4{]}^{2-}$

Due to excess addition of concentrated $HCl$ is $CoC{l}_2$ solution, a complex of cobalt is form which is $[CoC{l}_4{]}^{2-}$ which is of blue colour where as $CoC{l}_2$ is pink coloured.

Reaction:

$CoC{l}_2+2HCl\to [CoC{l}_4{]}^{-2}+H_2$