Question

Calculate the pH of a buffer solution made from 0.10 M citric acid and 0.25 M citrate, given an acid dissociation constant for citric acid equal to 1.8 x 10^-5.

Answer 1

Given:

1. Concentration of acid - 0.10 M

2. Concentration of conjugate base - 0.25 M

3. Ka = 1.8 * 10^-5

To find :

pH of buffer solution

Formula:

pH = pKa + log [base] / [acid]

Solution :

First we will calculate pKa from ka

pKa = - log Ka

= - log (1.8 * 10^-5)

= - (-4.7447)

pKa = 4.7447

Now we will use the formula

pH = pKa + log [base] / [acid]

= 4.7447 + log (0.25)/(0.10)

= 4.7447 + log (2.5)

= 4.7447+0.3979

pH = 5.1426

Hence pH of the buffer solution is 5.1426