Question

In the dissociation of $N{H}_{4}OH$, if $N{H}_{4}Cl$ is added what will be the change in $pH$ for the $N{H}_{4}OH$ solution ?

• A. Decreases
• B. Increases
• C. No change
• D. first decreases and then increases.

Answer 1

The correct option is A Decreases

The dissociation reaction for the weak base , $N{H}_{4}OH$ is :$N{H}_{4}OH\rightleftharpoons N{H}_4^{+}+O{H}^{-}$
Now , Ammonium chloride, is added to the solution. It is a strong electrolyte, which ionizes almost completely as follows: $N{H}_{4}Cl\rightleftharpoons N{H}_4^{+}+C{l}^{-}$
So with addition of $N{H}_{4}Cl$ the concentration of $N{H}_4^{+}$ is increased. Due to the common ion effect, the dissociation reaction of $N{H}_{4}OH$ is suppressed and consequently the concentration of $O{H}^{-}$ ions is decreased. As a result the basic character of the medium decreases or acid character increases.
If acid character increases the $pH$ of the medium will decrease.