Calculate [H3O+] given [OH ] in each aqueous solution and classify each solution as acidic or basic.
(a) [OH−] = 2.7 × 10−12M
(b) [OH−] = 2.5 × 10−2 M
(c) [OH−] = 1.1 × 10−10 M
(d) [OH−] = 3.3 × 10−4 M
Solution: Here, we are going to calculate hydronium ion concentration in each of the solution.
In pure water, one H2O molecule donates proton and acts as an acid and another water molecule accepts a proton and acts as a base at the same time. The following equilibrium exists:
H2O(l) + H2O(l) ------> H3O+(aq) + OH-(aq)
The equilibrium constant for the reaction is given by:
Kw= [H3O+][OH−] -----(1)
Where, Kw is called the ionic product of water and its value is 1 x 10-14 M2.
We can distinguish acidic, neutral and basic aqueous solutions by the relative values of the H3O+ and OH− concentrations:
Acidic: [H3O+] > [OH−]
Neutral: [H3O+] = [OH−]
Basic: [H3O+] < [OH−]
Step2:Given, [OH-] = 2.7 x 10-12 M
From equation (1), [H3O+] = Kw / [OH-]
[H3O+] = (1 x 10-14 M2) / (2.7 x 10-12 M)