Question

An aqueous buffer solution of volume 100 cm³ consists of 0.20 M CH₃COOH and 0.20 M NaCH₃CO₂.

pKa value of CH₃COOH is 4.75.

Predict the pH value of this solution. 3 sig.

Answer 1

The pH of the buffer solution consisting of equal concentrations of acetic acid (CH₃COOH) and sodium acetate (NaCH₃COO), with pKa of 4.75, is 4.75.

Step-by-step explanation:

The pH of the buffer solution is 4.75.

A buffer solution is made up of a weak acid and its conjugate base. In this case, we have acetic acid (CH₃COOH) and sodium acetate (NaCH₃COO). The pH of the buffer can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the base and [HA] is the concentration of the acid. Given that the concentrations of CH₃COOH and NaCH₃COO in the solution are equal (0.20 M), the ratio of [A-]/[HA] is 1. Because the logarithm of 1 is 0, the pH is equal to the pKa of acetic acid, which is 4.75.

Therefore, this buffer system is effective in maintaining a stable pH when small amounts of acid or base are added to the solution.