Question

The $pH$ of $0.1M$ solution of the following salts increases in the order

• A. $NaCl<N{H}_{4}Cl<NaCN<HCl$
• B. $HCl<N{H}_{4}Cl<NaCl<NaCN$
• C. $NaCN<N{H}_{4}Cl<NaCl<HCl$
• D. $HCl<NaCl<NaCN<N{H}_{4}Cl$

Answer 1

The correct option is B $HCl<N{H}_{4}Cl<NaCl<NaCN$

$NaCN$ is made up of strong base $NaOH$ and weak acid $HCN$. $C{N}^{-}$ forms $HCN$ accepting the $H^{+}$ from the water, so it increases the $O{H}^{-}$ concentration and hence, the pH increases.

$NaCl$ is neutral salt, its pH is around 7, as it is formed by strong base and strong acid.

$N{H}_{4}Cl$ is the salt of weak base and strong acid, so in solution the $N{H}_4^{+}$ forms the $N{H}_{4}OH$. $N{H}_{4}OH$ being a weak acid, $O{H}^{-}$ concentration decreases, hence, basic nature decreases and pH also decreases.

$HCl$ is a strong acid so it increases the H+ ion concentration , hence the $O{H}^{-}$ concentration decreases and therefore the pH is least.