Question

Addition of sodium hydroxide solution to a weak acid $\left(HA\right)$ results in a buffer of $pH=6$. If ionisation constant of $HA$ is ${10}^{-5}$, the ratio of salt to acid concentration in the buffer solution will be:

• A. $1:10$
• B. $4:5$
• C. $10:1$
• D. $5:4$

Answer 1

The correct option is C $10:1$

$K_a={10}^{-5}$

$p{K}_a=-log{K}_a=-log{10}^{-5}=5$

$pH=pKa+log\frac{\left[salt\right]}{\left[acid\right]}$

$6=5+log\frac{\left[salt\right]}{\left[acid\right]}$

$1=log\frac{\left[salt\right]}{\left[acid\right]}$

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

Hence, the option (C) is correct answer.