Browse Questions

# When ammonia is added to pure water, the concentration of which of the following species already present, will decrease

(a) $O^{2-}$

(b) $OH^-$

(c) $H_3O^+$

(d) $NH_4^+$

Answer: $H_3O^+$

In pure water, there is an equilibrium
$H_2O + H_2O \rightleftharpoons H_3O^+ + OH^-$

Addition of Ammonia disturbs this equilibrium because $NH_3$ reacts with $H_3O^+$ ions as
$NH_3 + H_3O^+ \rightleftharpoons NH^+_4 + H_2O$