Question

If the Ka of a monoprotic weak acid is 3.1 × 10-6, what is the pH of a 0.14 M solution of this acid?

Answer 1

pH is calculated by using following formula,

                              pH  =  - log [H⁺]

As we are not given with [H⁺], so we will calculate it bu using following formula,

                 [H⁺]  =  $\sqrt{Ka . M}$

Putting Values and solving,

                 [H⁺]  =  $\sqrt{1.3*10^-6 * 0.17}$

                 [H⁺]  =  $\sqrt{2.21*10^-7}$

                 [H⁺]  =  4.70 × 10⁻⁴

Now,
                 pH  =  - log (4.70 × 10⁻⁴)

                 pH  =  3.32