Question

The equilibrium, $2C{u}^I\rightleftharpoons C{u}^0+C{u}^{II}$, in aqueous medium at 25${}^{o}C$ shifts towards the left in the presence of:

• A. ${NO}_3^{-}$
• B. $C{l}^{-}$
• C. $SC{N}^{-}$
• D. $C{N}^{-}$

Answer 1

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

The correct options are
B $C{l}^{-}$
C $SC{N}^{-}$
D $C{N}^{-}$

$C{u}^{2+}$ ions react with $C{N}^{-}$ and $SC{N}^{-}$ ions forming $\left[Cu\right(CN{)}_4{]}^{3-}$ and $\left[Cu\right(SCN{)}_4{]}^{3-}$ leading the reaction in the backward direction.

$C{u}^{2+}+2C{N}^{-}\to Cu(CN{)}_2$

$2Cu(CN{)}_2\to 2CuCN+(CN{)}_2$

$CuCN+3C{N}^{-}\to \left[Cu\right(CN{)}_4{]}^{3-}$

$C{u}^{2+}+4SC{N}^{-}\to \left[Cu\right(SCN{)}_4{]}^{3-}$

$C{u}^{2+}$ also combines with $CuC{l}_2$ which reacts with Cu to produce CuCl pushing the reaction in backward direction.

$CuC{l}_2+Cu\to 2CuCl\downarrow$