Question

pH of the buffer containing $0.6g$ of acetic acid and $8.2g$ of sodium acetate in $1$ litre of water is: ($p{K}_a$ of acetic acid $=4.5$)

• A. $7.5$
• B. $4.5$
• C. $5.5$
• D. $6.5$

Answer 1

Answer: (B)

$4.5$

No. of moles in $1L$ of $0.10M$ acetic acid$=\frac{0.6}{60}=0.01$
No. of moles in $1L$ of $0.05M$ Sodium acetate$=\frac{8.2}{82}=0.1$
$\frac{[Sod.acetate]}{\left[aceticacid\right]}=\frac{0.01}{0.1}=0.1$
Applying the equation
$pH=\log \frac{\left[Salt\right]}{\left[Acid\right]}+p{K}_a$
$pH=\log 10+4.5$
or $pH=4.5$