Question

Why do solutions of a strong acid, and a strong base, which contain equimolar ${H_3}{O^ + }$ and $O{H^ - }$ , when mixed give rise to a solution that is pH neutral?

Answer 1

Strong acid is an acid that can easily or completely dissociate into ions to release ${H^ + }$ ions. Strong base is a base that can easily give hydroxide ion or abstraction of protons. pH is defined as the negative logarithm of the hydrogen ion concentration. Equimolar concentrations of ${H_3}{O^ + }$ and $O{H^ - }$gives a neutral solution.

Complete answer:
pH is defined as the negative logarithm of the hydrogen ion $\left[ {{H^ + }} \right]$ concentration the equation can be written as $pH = - \log \left[ {{H^ + }} \right]$
Given that a solution of a strong acid, and a strong base are taken with equimolar concentrations of ${H_3}{O^ + }$ and $O{H^ - }$ .
Strong acid and strong base with equimolar concentrations of ${H_3}{O^ + }$ and $O{H^ - }$ means the concentrations of strong base and strong acid are equal.
${H_3}{O^ + }$ known as hydronium ions that can be formed by reacting ${H^ + }$ with ${H_2}O$ . The term ${H_3}{O^ + }$ means it is an acidic compound. Hydroxide ion $\left( {O{H^ - }} \right)$ is released from basic compounds.
When a solution with equimolar concentrations of ${H_3}{O^ + }$ and $O{H^ - }$ are taken it results in the formation of two water molecules. The chemical reaction will be as follows:
${H_3}{O^ + } + O{H^ - } \to 2{H_2}O$
Thus, the solution will be a neutral pH solution as water is formed.

Note:
The negative part in the strong acid and the positive part in the strong base reacts to give a corresponding salt. Whereas the hydronium ion and hydroxide ion react to give two molecules of water which has a pH value of $7$ and can be a neutral solution.