Question

The $pH$ value of $0.001{\text{ }}M$ aqueous solution of ${\text{NaCl}}$ is:
A ) 7
B ) 4
C ) 11
D ) unpredictable

Answer 1

Determine the type of salt for sodium chloride. Types of salt includes salt of strong acid with strong base, or salt of strong acid with weak base, or salt of weak acid with strong base, or salt of weak acid with weak base. Then determine whether cation or anion undergoes hydrolysis or neither ion goes hydrolysis. Based on this, determine if the solution is acidic or basic or neutral.

Complete step by step answer:
Sodium chloride is obtained by the reaction of hydrochloric acid with sodium hydroxide.

${\text{HCl + NaOH }} \to {\text{ NaCl + }}{{\text{H}}_2}{\text{O}}$

Both hydrochloric acid and sodium hydroxide are strong acids. They are completely ionized in aqueous solution.
Sodium chloride is the salt of strong base (sodium hydroxide) with strong acid (hydrochloric acid). Such salts do not undergo hydrolysis in aqueous solution. Neither sodium cation, nor chloride anion undergoes hydrolysis in aqueous solution. Since sodium chloride does not hydrolyze in aqueous medium, it neither gives protons, nor does it give hydroxide ions. Hence, 0.001 M aqueous solution of sodium chloride is neutral with $pH{\text{ }}7$ .

Hence, the option A is the correct answer

Additional information: For salts of weak acid with strong base, the anion undergoes hydrolysis in aqueous solution to produce hydroxide ions. The solution is basic with $pH$ greater than 7. An example of such salt is sodium acetate.
For salts of strong acid with weak base, the cation undergoes hydrolysis in aqueous solution to produce hydronium ions. The solution is acidic with $pH$ less than 7. An example of such salt is ammonium chloride.
For salts of weak acid with weak base, the relative strengths of weak acid and weak base determine the $pH$ of the solution.

Note:
A neutral solution has $pH$ equal to 7 and $pOH$ equal to 7. Such a solution contains an equal number of hydronium ions and hydroxide ions. An acidic solution has $pH$ less than 7 and $pOH$ greater than 7. Such a solution contains more number of hydronium ions than the number of hydroxide ions. A basic solution has $pH$ greater than 7 and $pOH$ less than 7. Such a solution contains more number of hydroxide ions than the number of hydronium ions.