Question

$100$ mL of $0.01$ M $C{H}_{3}COOH$ and $200$ mL of $0.02$ M $C{H}_{3}COONa$ are mixed to form a buffer solution. $700$ mL of water is added to this solution. The pH before and after dilution are:
(pKa = 4.74, log 4 =0.6)

• A. $5.04,5.04$
• B. $5.04,0.504$
• C. $5.34,0.534$
• D. $5.34,5.34$

Answer 1

The correct option is D $5.34,5.34$

Here we are given an acidic buffer. So
$pH=pKa+log\frac{\left[\text{salt}\right]}{\left[\text{acid}\right]}$
$=4.74+log\frac{200\times 0.02}{100\times 0.01}$
$=4.74+log4=5.34$
Dilution has no effect on pH of buffer solution, hence pH after dilution will also be $5.34$