Chemistry question

Question

If a buffer solution is 0.210 M in a weak acid (𝐾a=3.4×10−5) and 0.420 M in its conjugate base, what is the pH?



Answer 1

Use the Henderson Hasselbalch equation:

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

pKa = -log Ka = 4.47

pH = 4.47 + log [0.420]/[0.210]

pH = 4.47 + log 2

pH = 4.7 + 0.30

pH = 5.00