Question

The half‑equivalence point of a titration occurs half way to the equivalence point, where half of the analyte has reacted to form its conjugate, and the other half still remains unreacted. If 0.440 moles of a monoprotic weak acid ( K a = 8.3 × 10 − 5 ) is titrated with NaOH , what is the pH of the solution at the half‑equivalence point?

Answer 1

Answer : The pH of solution at the half‑equivalence point is, 4.1

Explanation :

As we known that the titration takes place between strong base and weak acid.

So, at half‑equivalence point of a titration the pH of the solution is equal to the $pK_a$ of weak acid.

As we are given:

$K_a=8.3\times 10^{-5}$

Now we have to calculate the value of $pK_a$.

The expression used for the calculation of $pK_a$ is,

$pK_a=-\log (K_a)$

Now put the value of $K_a$ in this expression, we get:

$pK_a=-\log (8.3\times 10^{-5})$

$pK_a=5-\log (8.3)$

$pK_a=4.1$

Thus, $pH=pK_a=4.1$

Therefore, the pH of solution at the half‑equivalence point is, 4.1