Question

Calculate the pH of a solution prepared by mixing 0.0870 mol of chloroacetic acid plus 0.0280 mol of sodium chloroacetate in 1.00 L of water. First do the calculation by assuming that the concentrations of HA and A− equal their formal concentrations. The pKa of chloroacetic acid is 2.865.

Answer 1

Answer:

pH = 2.373

Explanation:

Step 1: Calculate the molar concentrations of the species present

[chloroacetic acid] = 0.0870 mol / 1.00 L = 0.0870 M

[sodium chloroacetate] = 0.0280 mol / 1.00 L = 0.0280 M

Sodium chloroacetate is a strong electrolyte, so the concentration of chloroacetate is 0.0280 M.

Step 2: Calculate the pH of the solution

We have a buffer system formed by a weak acid (chloroacetic acid) and its conjugate base (chloroacetate). We can calculate the pH of the solution using the Henderson-Hasselbach equation.

pH = pKa + log [chloroacetate]/[chloroacetic acid]

pH = 2.865 + log 0.0280 M/0.0870 M

pH = 2.373