Question

Calculate the value of pH when 2 mol of acetic acid is titrated with 0.5 mol of sodium hydroxide. (acetic acid pKa=4.75)

Answer 1

This is a problem of titration of weak acid with a strong base.

Using Henderson equation, we can determine the pH of the solution.

We know that,

p^{​​​​​​H} = p^{​​​​​​K_​​​a} + log([salt]/[acid]) where, p^{​​​​​​K_{​​​​​a}}​ = dissociation constant of acid

Here, 2 mol acetic acid i.e. CH_{​​​​​3} COOH is titrated with a strong base i.e. 0.5 mol NaOH.

0.5 mol NaOH will produce 0.5 mol OH^(-) .

This 0.5 mol OH^(-) base will react with 0.5 mol acetic acid to give 0.5 mol sodium acetate salt.

Hence, the concentration of acetate ion in the solution will be 0.5 mol/lit

And, the concentration of acid is 2-0.5 = 1.5 mol/lit.

The p^{​​​​​​H} = 4.76 + log(0.5/1.5) = 4.28

Hence, the answer is 4.28.