Question

The ionisation constant of a weak acid is$1\times {10}^{-6}$ The pH of the buffer obtained by adding 0.2 moles of its salt with strong base to 1 litre of 0.1 M solution of acid is:

• A. 6.3
• B. 7.7
• C. 7
• D. 4.5

Answer 1

Answer: (A)

6.3

The expression for the pH of the acidic buffer solution is as given below.
$pH=p{K}_a+log\frac{\left[salt\right]}{\left[acid\right]}$

where, $p{K}_a=-log{K}_a=-log(1\times {10}^{-6})=6$
Substitute values in the above equation.
$pH=6+log\frac{0.2}{0.1}=6.3$.