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

At 25⁰ C, K_w = 1.00 x 10^-14 = [H₃O⁺] [OH^-]; or, [H₃O⁺] = K_w / [OH^-] and [OH^-] =K_w/ [H₃O⁺].

So, in Solution A: [H₃O⁺] = 1.00 x 10^-14 / 2.97 x 10^-7 = 3.37 x 10^-8 M;

And for Solution B: [OH^-] = 1.00 x 10^-14 / 8.37 x 10^-9. = 1.19x 10^-6 M

Finally, Solution C: [OH^-] = 1.00 x 10^-14 / 7.51 x 10^-4 = 1.33 x 10^-11 M