Question

The pH value of an acid is $5$ and its concentration is 1 M. What is the value of $ K_{a} $ for the acid?

• A. $10^{-7}$
• B. $10^{-5}$
• C. $10^{-10}$
• D. $10^{-8}$

Answer 1

Answer: (C)

By using $pH =-\log \sqrt{K_{a} \cdot C}$
$5=-\log \sqrt{K_{a} \times 1} =-\frac{1}{2} \log K_{a} $
$\log K_{a} =-10 $
$K_{a} =10^{-10}$
Hence, dissociation constant $(K_a) = 10^{-10}$