Question

A complex compound of $C{o}^{3+}$ with molecular formula $CoC{l}_x\cdot yN{H}_3$ gives a total of $3$ ions when dissolved in water. How many $C{l}^{-}$ ions satisfy both primary and secondary valencies in this complex?

• A. 3
• B. 1
• C. 4
• D. zero

Answer 1

Answer: (B)

As cobalt is present as $C{o}^{3+}$ and co-ordination number of cobalt is $6$, the molecular formula of compound should be $CoC{l}_3\cdot yN{H}_3$.
Now, as it gives a total of $3$ ions when dissolved in water, its structural formula must be $\left[CoCl{\left(N{H}_3\right)}_5\right]C{l}_2$
$\left[CoCl{\left(N{H}_3\right)}_5\right]C{l}_2\rightleftharpoons {\left[CoCl{\left(N{H}_3\right)}_5\right]}^{2+}+2C{l}^{-}$
Thus only one $C{l}^{-}$ ion is satisfying both primary and secondary valency of $C{o}^{3+}$ in this compound.