Question

A weak base BOH is titrated with a strong acid HA. When 10ml of HA is added, the pH is found to be 9.00 and when 25 ml is added, pH is 8.00. The volume of the acid required to reach the equivalence point

• A. 35 ml
• B. 40 ml
• C. 30 ml
• D. 50 ml

Answer 1

The correct option is C

30 ml

$pH=14-p{K}_b-log\frac{\left[B^{+}\right]}{\left[BOH\right]}$
V = volume of acid required for the equivalence point.
$i\left)\right(pH{)}_1=9=14-p{K}_b-log\frac{10}{V-10}ii\left)\right(pH{)}_2=8=14-p{K}_b-log\frac{25}{V-25}\left(i\right)-\left(ii\right),1=log\frac{25}{V-25}-log\frac{10}{V-10}=log\frac{25(V-10)}{10(V-25)}\Rightarrow V=30ml$