Question

What is the $K_a$ value of the citric acid + NaOH titration?

Answer 1

Hint: The titration is between citric acid and NaOH (sodium hydroxide) in which citric acid is a weak acid and sodium hydroxide is a strong base. When the titration takes place between a weak acid and a strong base then we get two equivalence points.

Complete answer:
Titration is a process in which we get the neutralization point, by adding a specific amount of base into a specific concentration of acid. When the acid and base are strong then we get a sharp equivalence. The titration is between citric acid and NaOH (sodium hydroxide) in which the citric acid is a weak acid and sodium hydroxide is a strong base. When the titration takes place between a weak acid and a strong base then we get two equivalence points, i.e., before the equivalence and after the equivalence.
When we take 0.1 M NaOH and 0.1 M citric acid, then we get 5.8 ml as the first equivalence point and 16.0 ml as the second equivalence point.
So, there will be two $K_a$ values for citric acid which can help to find the pH of the solution.
$7.4\text{ x 1}{\text{0}}^{-3}$ is the first $K_a$ value of citric acid and pH is nearly equal to the $p{K}_a$
$pH\approx p{K}_a=-\log (7.4\text{ x 1}{\text{0}}^{-3})=2.13$
$1.7\text{ x 1}{\text{0}}^{-5}$ is the second $K_a$ value of citric acid. So the pH will be:
$pH\approx p{K}_a=-\log (1.7\text{ x 1}{\text{0}}^{-5})=4.77$

Note:
While we plot the graph of pH and volume of the titrant of the titration between a weak acid or base and strong acid or base, then the curve is difficult to study so the equivalence points are difficult to differentiate.