Question

a What is the pH of a solution that has a formic acid concentration of 0.020 M and a sodium formate concentration of 0.060 M? pH =

Answer 1

Formic acid is a weak acid. It has a pKa of 3.75. Now a mixture of formic acid with its corresponding salt will give a buffer mixture.

Thus here the formic acid and sodium formate mixture is a type of acidic buffer solution.

To find out the pH of this solution we have to apply the Henderson equation, which looks like:

$pH=pK_{a}+log\frac{[salt]}{[acid]}$

Where the terms in the parentheses denote the concentrations of the salt and acid.

Now given terms are, pKa = 3.75; [formic acid] = 0.020 M; [sodium formate] = 0.060 M

Thus, $pH=3.75+log\frac{0.060}{0.020}$

$=>pH=4.22$

$\therefore$ The pH of the solution is = 4.22