Question

Calculate pH of a buffer prepared by adding $10mL$ of $0.10M$ acetic acid to $20mL$ of $0.1M$ sodium acetate.

$[p{K}_a\left(C{H}_{3}COOH\right)=4.74]$

• A. $3.00$
• B. $4.44$
• C. $4.74$
• D. $5.04$

Answer 1

The correct option is D $5.04$

Millimoles of $C{H}_{3}COOH=0.1\times 10=1.0$

Millimoles of $C{H}_{3}COONa=0.1\times 20=2.0$

From, Henderson Hasselbalch equation,

$pH=p{K}_a+\log \frac{\left[conjugatebase\right]}{\left[acid\right]}=4.74+\log \frac{2}{1}=4.74+0.30=5.04$