A buffer solution of pH 4.58 is to be prepared from acetic acid (Ka = 1.80 x 10-5, sodium acetate and water. Find be the molar ratio of acetate ion to acetic acid in this solution to obtain this pH?

Answer 1

Use the Henderson Hasselbalch equation: pH = pKa + log [conjugate base][acid]

pKa = -log Ka = -log 1.80x10^-5 = 4.74

pH = pKa + log [conjugate base][acid]

4.58 = 4.74 + log (conj.base/acid)

-0.16 = log (conj.base/acid)

[conjugate base]/[acid] = 0.692 = molar ratio of acetate to acetic acid