Question

Calculate the concentration of sodium benzoate that must be present in a 0.20 M solution of benzoic acid (C6H5COOH, Ka = 6.5 × 10-5) to produce a pH of 4.00. The ionization (dissociation) equation is shown below.

C6H5COOH(aq) + H2O (aq) <--> C6H5COO– (aq) + H3O+ (aq)

Answer 1

To calculate the concentration of sodium benzoate needed to produce a pH of 4.00 in a 0.20 M solution of benzoic acid, you can use the Henderson-Hasselbalch equation.

Step-by-step explanation:

To calculate the concentration of sodium benzoate needed to produce a pH of 4.00 in a 0.20 M solution of benzoic acid, we can use the Henderson-Hasselbalch equation:

pH = pKa + log([C6H5COO-]/[C6H5COOH])

Given that the Ka value for benzoic acid is 6.5 × 10-5, we can rearrange the equation to solve for [C6H5COO-]:

[C6H5COO-]/[C6H5COOH] = 10^(pH - pKa)

Plugging in the pH value of 4.00 and the pKa value of 6.5 × 10-5, we can calculate the concentration of sodium benzoate needed.