Calculate either [H3O+] or [OH−] for each of the solutions at 25 °C.

Question

Solution A: [OH^−] =2.97×10^−7 M; [H3O^+] = M

Solution B: [H3O^+] =8.37×10^−9 M; [OH−] = M

Solution C: [H3O^+] =7.51×10^−4 M; [OH−] = M

Answer 1

Solution A: [H₃O⁺] = 3.37 x 10^-8 M

Solution B: [OH^-] = 1.19 x 10^-6 M

Solution C: [OH^-] = 1.33 x 10^-11 M

In all aqueous solutions the relationship between H⁺ and OH^- ion concentrations is given by the equation:

[H₃O⁺] [OH^-] = K_{w. …………..(1)}

At 25^oC K_w value is 1.0 x 10^-14

In each case substitute the values of K_w and given concentration of either H⁺ or OH^- in equation (1), you get the value for the unknown.

P.S. when the concentrations in molarity are low enough, molar concentration and activity(effective concentration) are considered equal/close enough.