Question

The ionisation constant of an acid, K_a, is the measure of strength of an acid. The K_a values of acetic acid, hypochlorous acid and formic acid are 1.74 × 10^–5, 3.0 × 10^–8 and 1.8 × 10^–4 respectively. Which of the following orders of pH of 0.1 mol dm^–3 solutions of these acids is correct?

Options

• Acetic acid > Hypochlorous acid > Formic acid

• Hypochlorous acid > Acetic acid > Formic acid

• Formic acid > Hypochlorous acid > Acetic acid

• Formic acid > Acetic acid > Hypochlorous acid

Answer 1

Formic acid > Acetic acid > Hypochlorous acid

Explanation:

Higher the value of K_a higher will be the acidic strength K_a value for formic acid is highest and that will be of hypochlorous acid is lowest.