Question

The pH value of ${10^{ - 3}}M$ aqueous solution of ${\text{NaCl}}$ is:
A. 7
B. 3
C. 11
D. 14

Answer 1

Identify the type of the salt to which ${\text{NaCl}}$ belongs. The type of salt includes (i) the salt of strong acid with strong base (ii) the salt of strong acid with weak base (iii) the salt of weak acid with strong base (iv) the salt of weak acid with weak base

Complete answer:
The chemical formula ${\text{NaCl}}$ represents the salt sodium chloride. It is the salt of hydrochloric acid with sodium hydroxide. Hydrochloric acid is a strong acid. Sodium hydroxide is a strong base. Thus, sodium chloride is a salt of strong acid with strong base. Salt of strong acid with strong base does not undergo hydrolysis in aqueous solution. Such salts form neutral aqueous solution with ${\text{pH = 7}}$ and $\left[ {{{\text{H}}_3}{{\text{O}}^ + }} \right] = \left[ {{\text{O}}{{\text{H}}^ - }} \right] = {10^{ - 7}}M$ .
Thus, the aqueous sodium chloride solution is a neutral solution with equal concentration of hydronium ions and hydroxide ions. Aqueous sodium chloride solution has pH equal to 7.

**Hence, the correct option is the option (A).

Note:**
(i) The salt of strong acid with strong base forms a neutral aqueous solution with pH of 7. Hydronium ion concentration is equal to the hydroxide ion concentration.
(ii) The salt of strong acid with weak base forms acidic aqueous solution with pH being less than 7. Hydronium ion concentration is greater than hydroxide ion concentration.
(iii) The salt of weak acid with a strong base forms an alkaline aqueous solution with pH being greater than 7. Hydroxide ion concentration is greater than hydronium ion concentration.
(iv) The salt of weak acid with weak base forms an aqueous solution whose pH depends on the relative strengths of the weak acid and the weak base.