The K_a of benzoic acid is 6.30 × 10^-5. The pH of a buffer prepared by combining 50.0 mL of 1.00 M potassium benzoate and 50.0 mL of 1.00 M benzoic acid is ________. A)1.705 B)0.851 C)3.406 D)4.201 E)2.383

Question

Quizplus · Accepted Answer

First, use the Henderson-Hasselbalch equation to find the pH of the buffer.

pH = pKa + log([A-]/[HA])

pKa = -log(Ka) = -log(6.30 × 10^-5) = 4.201

[HA] = 1.00 M x (50.0mL/100.0mL) = 0.500 M

[A-] = 1.00 M x (50.0mL/100.0mL) = 0.500 M

pH = 4.201 + log(0.500/0.500) = 4.201

Therefore, the pH of the buffer is 4.201. The answer is (D).

The Ka of Benzoic Acid Is 6

The K_a of Benzoic Acid Is 6