What is the buffer component ratio, ([CH3COO-]/[CH3COOH]) of an acetate buffer that has a pH of 4.57. Ka of CH

Question

What is the buffer component ratio, ([CH3COO-]/[CH3COOH]) of an acetate buffer that has a pH of 4.57. Ka of CH3COOH is 1.8 x 10-5.

Answer 1

All you do here is use the Henderson Hasselbalch equation. Remember that CH3COO- is deprotonated so it is a conjugate base and CH3COOH is an acid.

Convert Ka to pKa

Ka = -log(Ka)

Ka = -log(1.8*10^-5)

Ka = 4.74

pH = pKa + log(base/acid)

4.57 = 4.74 + log([CH3COO-]/[CH3COOH])

-.1747 = log([CH3COO-]/[CH3COOH])

10^(-.1747) = 10^(log([CH3COO-]/[CH3COOH]))

([CH3COO-]/[CH3COOH]) = .6688