If a buffer solution is 0.200 M in a weak acid ( 𝐾a=2.2×10−5) and 0.440 M in its conjugate base, what is the pH?

Answer 1

pH = pKa + log [conj. base] / [acid]

pKa = -log Ka = -log 2.2x10^-5 = 4.66

pH = 4.66 + log (0.440 / 0.200)

pH = 4.66 + log 2.2

pH = 4.66 + 0.34

pH = 5.00

Answer 2

Renata,

To solve this question you can use the Henderson-Hasselbach equation:

pH = pK_a + log ([conjugate base]/[acid])

You can plug the numbers you have in the question in their respective places to get the pH.

pK_a = - log K_a