Question

What is the pH of 0.5 litre buffer solution containing 0.01 mole of CH₃COOH and 0.01 mole of CH₃COONa?

[pK_a of acid = 4.74]

Options

• 2.74

• 3.74

• 4.74

• 5.74

Answer 1

4.74

Explanation:

pH of an acidic buffer is given by Henderson-Hasselbalch equation as:

pH = `"pK"_"a" + log_10  (["salt"])/(["acid"])`

[Salt] = `0.01/0.5` = 0.02 M

[Acid] = `0.01/0.5` = 0.02 M

∴ pH = `"pK"_"a" + log_10  0.02/0.02`

∴ pH = 4.74