Question

A buffer solution contains 0.1 mole of sodium acetate in $1000c{m}^3$ of 0.1 M acetic acid. To the above buffer solution, 0.1 mole of sodium acetate is further added and dissolved. The $pH$ of the resulting buffer is equal to:

• A. $p{K}_a-\log 2$
• B. $p{K}_a$
• C. $p{K}_a+2$
• D. $p{K}_a+\log 2$

Answer 1

The correct option is D $p{K}_a+\log 2$

Initially:

$\left[C{H}_{3}COONa\right]=0.1M$
$\left[C{H}_{2}COOH\right]=0.1M$

When 0.1 mol $C{H}_{3}COONa$ is added
$\left[C{H}_{2}COONa\right]=0.1+0.1=0.2M$

$\left[C{H}_{2}COOH\right]=0.1M$

Now,

$pH=p{K}_a+\log \frac{\left[salt\right]}{\left[acid\right]}$

$=p{K}_a+\log \frac{0.2}{0.1}=p{K}_a+\log 2$