Answer to Question #91252 in Inorganic Chemistry for Agou Alier

Question

The pH of a 0.0516 M solution of nitrous acid, HNO2, is 2.34. What is its Ka?

Answer 1

Solution.

Nitrous acid is a very weak acid, so you need to write the following formula:

$pH = \frac{pKa}{2} - \frac{lg(H+)}{2}$

$pKa = 2 \times (pH + \frac{lg(H+)}{2})$

$pKa = 2 \times (2.34 + \frac{lg(0.0516)}{2})$

pKa = 3.39

$pKa = -lg(Ka)$

$Ka = 10^{-pKa}$

$Ka = 4.07 \times 10^{-4}$

Answer:

$Ka = 4.07 \times 10^{-4}$