Question

If $p{K_a}$ of acetic acid is 4.74. The concentration of $C{H_3}COONa$ is 0.01M. The pH of $C{H_3}COONa$ solution is?
A. 10.37
B. 8.37
C. 7.0
D. 4.37

Answer 1

The reaction taking place in this question is a neutralization reaction as acetic acid is reacting with sodium hydroxide to form sodium salt of acetic acid and water. The salt formed in this reaction is a basic salt.

Complete step by step answer:
In the question, it is given that the $p{K_a}$ of the acid is 4.74. The concentration of sodium salt of acetic acid $C{H_3}COONa$ is 0.01 M.
The reaction between the acid and the base results in the formation of salt and water. The reaction is known as neutralization reaction.
The acetic acid reacts with sodium hydroxide to form sodium salt of acetic acid. The acetic acid is a weak acid and sodium hydroxide is a strong base. When a weak acid reacts with a strong base, so the salt which is formed is a basic salt.
The $p{K_a}$ is the negative logarithm of base 10 of the acid dissociation constant denoted by ${K_a}$ .
The $p{K_a}$ is given as shown below.
$pKa = - {\log _{10}}{K_a}$
To calculate the pH of the strong base and weak acid, the expression is given as shown below.
$pH = 7 + \dfrac{1}{2}p{K_a} + \dfrac{1}{2}\operatorname{logC}$
Where,
C is the concentration.
To calculate the pH of salt, substitute the values in the above expression.
$\Rightarrow pH = 7 + \dfrac{1}{2}(4.74) + \dfrac{1}{2}\log (0.01)$
$\Rightarrow pH = 8.37$

So, the correct answer is Option b.

Note: As we know that the salt is neutral in nature. The pH of the neutral salt is 7. But in this case, the salt formed by the reaction of weak acetic acid and strong sodium hydroxide is a basic salt that’s why the calculated pH of the salt $C{H_3}COONa$ is more than 7.