For an acidic buffer, we use the Henderson-Hasselbalch equation:
pH=pKa+log‌| [‌ Salt ‌] |
| [‌ Acid ‌] |
Let
x be the concentration of the potassium acetate solution in molarity
(M).
Calculate the moles of acetic acid:
20 mL of 0.1 M acetic acid contains:
20×0.1=2 millimoles
Calculate the moles of potassium acetate:
50 mL of
xM potassium acetate contains:
50x millimoles
Given the pH is 4.8, substitute the values into the Henderson-Hasselbalch equation:
4.8=−(log‌1.8×10−5)+log‌Solve for
x :
log‌25‌x=0.06x=0.04MThus, the concentration of potassium acetate is 0.04 M .