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A complex compound of $\mathrm{Co}^{3+}$ with molecular formula $\mathrm{CoCl}_{\mathrm{x}} \cdot \mathrm{yNH}_3$ gives a total of 3 ions when dissolved in water. How many $\mathrm{Cl}^{-}$ions satisfy both primary and secondary valencies in this complex?
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As cobalt is present as $\mathrm{Co}^{3+}$ and co-ordination number of cobalt is 6 , the molecular formula of compound should be $\mathrm{CoCl}_3 \cdot \mathrm{yNH}_3$. Now, as it gives a total of 3 ions when dissolved in water, its structural formula must be $\left[\mathrm{CoCl}\left(\mathrm{NH}_3\right)_5\right] \mathrm{Cl}_2$
$\left[\mathrm{CoCl}\left(\mathrm{NH}_3\right)_5\right] \mathrm{Cl}_2 \rightleftharpoons\left[\mathrm{CoCl}\left(\mathrm{NH}_3\right)_5\right]^{2+}+2 \mathrm{Cl}^{-}$
Thus only one $\mathrm{Cl}^{-}$ion is satisfying both primary and secondary valency of $\mathrm{Co}^{3+}$ in this compound.
$\left[\mathrm{CoCl}\left(\mathrm{NH}_3\right)_5\right] \mathrm{Cl}_2 \rightleftharpoons\left[\mathrm{CoCl}\left(\mathrm{NH}_3\right)_5\right]^{2+}+2 \mathrm{Cl}^{-}$
Thus only one $\mathrm{Cl}^{-}$ion is satisfying both primary and secondary valency of $\mathrm{Co}^{3+}$ in this compound.
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