Question

The pH of a solution obtained by mixing 20 ml of 0.02 M $C{H}_{3}COONa$ and 10 ml of 0.01 M $C{H}_{3}COOH$ is $(p{K}_a=4.75)$

• A. 4.75
• B. 5.05
• C. 4.45
• D. 5.34

Answer 1

The correct option is D 5.34

Total volume after mixing = 30 ml
$C{H}_{3}COONa$ : No. of m mol before mixing = $[0.02\times 20]$
Concentration after mixing = $\frac{[0.02\times 20]}{30}$
$C{H}_{3}COOH$ : No. of m mol before mixing = $[0.01\times 10]$
Concentration after mixing = $\frac{[0.01\times 10]}{30}$
$\therefore pH=p{K}_a+log\frac{\left[salt\right]}{\left[acid\right]}$
$=4.75+log\frac{\frac{[0.02\times 20]}{30}}{\frac{[0.01\times 10]}{30}}=4.75+2log2=5.34$