Question

When sodium acetate $(C{H_3}COONa)$ is added to aqueous solution of acetic acid $(C{H_3}COOH)$
A.The pH value becomes zero
B.pH value remains unchanged
C.pH value decreases
D.pH value increases

Answer 1

:Hint: pH of a substance determines whether a substance is acidic or basic in nature. It is calculated on the basis of a pH scale. If the concentration of the ${H^ + }$ ions decreases, then the pH value also decreases which means it is acidic in nature and if the concentration of the ${H^ + }$ ions increases then the pH value also increases and thus, it is basic in nature.

Complete step by step answer:
The pH is a quantity which describes the chemical condition of a substance in nature. It gives us the extent of acidity and basicity of a substance. It also determines the behavior and properties of the substance and its applications and reactivity. The acidity and basicity of a substance is determined on the basis of a scale which ranges from $0 - 14$ in which if the pH of a substance is ranges below the value of $7$, then the substance is said to be acidic in nature and if it ranges more than $7$, then it is said to be basic and a value equal to $7$ on the pH scale determines that the substance is neutral in nature. That is it is neither an acid nor a base like water. So, if the concentration of the ${H^ + }$ ions decreases, then the pH value also decreases which means it is acidic in nature and if the concentration of the ${H^ + }$ ions increases then the pH value also increases and thus, it is basic in nature.
For the above question,
$C{H_3}COONa$ is obtained from the reaction of $NaOH$ and $C{H_3}COOH$
Thus, when $C{H_3}COONa$ionizes, it forms
$C{H_3}COONa \to C{H_3}CO{O^ - } + N{a^ + }$
When sodium acetate is added to a solution of acetic acid then the concentration of ${H^ + }$ ions decreases as the concentration of salt increases in the buffer solution and thus, the value of pH increases.

So, the correct option is (D).

Note:
When a weak acid and its salt is added to solution then an acidic buffer forms, similarly when a weak base and its salt is added to the solution then a basic buffer is formed. Blood has a pH value of about $7.35 - 7.40$ . Negative pH and a pH value above $14$ may also exist but the measuring scale only measures a value from $0 - 14$