Question

The equilibrium $2C{u}^1\rightleftharpoons C{u}^{\circ }+C{u}^{ll}$ in aqueous medium at $25^{\circ }C$ shifts towards the left in the presence of

• A. $N{O}_3^{-}$
• B. $C{l}^{-}$
• C. $SC{N}^{-}$
• D. $C{N}^{-}$

Answer 1

Answer: (B), (C), (D)

$C{u}^{2+}$ ions will react with $C{N}^{-}$and $SC{N}^{-}$forming ${\left[Cu(CN{)}_4\right]}^{3-}$ and ${\left[Cu(SCN{)}_4\right]}^{3-}$ leading the reaction in the backward direction.
$C{u}^{2+}+2C{N}^{-}\to Cu(CN{)}_2$
$2Cu(CN{)}_2\to 2CuCN+(CN{)}_2$
$CuCN+3C{N}^{-}\to {\left[Cu(CN{)}_4\right]}^{3-}$
$C{u}^{2+}+4SC{N}^{-}\to {\left[Cu(SCN{)}_4\right]}^{3-}$
$C{u}^{2+}$ also combines with $CuC{l}_{3-}$ which reacts with $Cu$ to produce $CuCl$ pushing the reaction in the backward direction.
$CuC{l}_2+Cu\to 2CuCl\downarrow$