Question

Be sure to answer all parts. What is the [H3O+] and the pH of a benzoic acid-benzoate buffer that consists of 0.22 M C6H5COOH and 0.41 M C6H5COONa? (Ka of benzoic acid = 6.3 × 10−5) Be sure to report your answer to the correct number of significant figures.

Answer 1

Answer:

The pH will be 4.5

Explanation:

The mixture of benzoic acid (weak acid) and its salt will make a buffer.

The pH of buffer solution can be calculated using Henderson Hassalbalch's equation, which is

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

pKa = -logKa

pKa = -log($6.3X10^{-5}$)

pKa = 4.2

$pH=4.2 + log\frac{0.41}{0.22}=4.2+0.27=4.47=4.5$