Question

Calculate the ph of a solution that is 0.245m benzoic acid and 0.170m sodium benzoate, a salt whose anion is the conjugate base of benzoic acid.

Answer 1

Hello!

A solution of a weak acid and its conjugate base is called a buffer solution. It can resist the addition of bases and acids while maintaining the pH approximately constant.

To calculate the pH of a buffer solution, we'll use the famous Henderson-Hasselbach equation, applying the pKa value of the Benzoic Acid (4,20). In this equation, [A⁻] represents the concentration of the Conjugate Base and [HA] the concentration of the acid.


`pH=pKa + log( ( [A^(-)])/([HA]) ) \\ \\ pH=4,20 + log ( (0,170 M)/(0,245) ) \\ \\ pH=4,04`

So, the pH of the solution would be 4,04.

Have a nice day!