Question

Th pH of 0.1 M solution of the following substances 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 $HCl<N{H}_{4}Cl<NaCl<NaCN$

The characteristics of the given solutions are:
NaCl is neutral since it is formed by strong acid (HCl) and strong base (NaOH). Hence it pH will be 7.
$N{H}_{4}Cl$ is slightly acidic as it produces $H^{+}$ due to the following reaction
$N{H}_4^{+}+H_{2}O\rightleftharpoons N{H}_{4}OH+H^{+}$
NaCN - slightly alkaline due to the following reaction
$C{N}^{-}+H_{2}O\rightleftharpoons HCN+O{H}^{-}$
HCl - highly acidic
The pH of the solution increases in the order of
highly acidic < slightly acidic < neutral < slightly alkaline
i.e., $HCl<N{H}_{4}Cl<NaCl<NaCN$