BITSAT 2024 Shift 1 Paper

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)+log‌

50x

2

Solve for x :
log‌25‌x=0.06
x=0.04M
Thus, the concentration of potassium acetate is 0.04 M .