Question

An aqueous solution of $CoC{l}_3.6N{H}_3$ on mixing with $AgN{O}_3$ produces $3$ moles of a white precipitate. Primary and secondary valency of the metal in this complex is:

• A. $3,6$
• B. $2,6$
• C. $3,3$
• D. $6,4$

Answer 1

The correct option is A $3,6$

$CoC{l}_3.6N{H}_3+3AgN{O}_3⟶\underset{\left(whiteppt\right)}{3AgCl}$

Here, we can see that $CoC{l}_3.6N{H}_3$ is the only source of $C{l}^{-}$ ions. If we obtain `3` moles of AgCl, it means `3` moles of $C{l}^{-}$ ions were obtained from $CoC{l}_3.6N{H}_3$. Hence, we can say that they were all outside the coordination sphere.
We can rewrite the formula of the said salt as $\left[Co\right(N{H}_3{)}_6]C{l}_3$.

On balancing the charges, we can comfortably say that `Co` is in `+3` oxidation state. Hence, its primary valency is `3`.
The coordination number of `Co` in the complex is `6`. Hence, we can say that the secondary valency is `6`.