Question

The $pKa$ of acid $X$ is $5$. The pH of a solution containing acid $X$ and its conjugate base is $6$. What is the ratio of the concentration of conjugate base to the concentration of acid? (conjugate base: acid)

• A. $1:2$
• B. $2:1$
• C. $1:10$
• D. $10:1$

Answer 1

Answer: (D)

$10:1$

Solution of acid $X$ and its conjugate base is a buffer solution, as this conjugate base is a part of a salt of this acid and a strong base.

For, this acidic buffer,

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

$\therefore \frac{\log \left[conjugatebase\right]}{\left[acid\right]}=pH-pKa=6-5=1$

$\therefore \frac{\left[Conjugatebase\right]}{\left[acid\right]}=\frac{10}{1}$