Calculate the hydroxide ion concentration, [OH−] , for a solution with a pH of 11.25 .

Answer 1

Since pH + pOH = 14, we can first find the pOH from a pH of 11.25

pOH = 14 - 11.25

pOH = 2.75

Since pOH = -log of [OH^-], we can write [OH-] = 1x10^-2.75

And converting this to a more conventional form, we have ...

[OH^-] = 1.78x10^-3 M

If you'd prefer, you can get the same answer a different way:

pH = 11.25 which means [H+] = 1x10^-11.25 = 5.62x10^-12 M

[H⁺][OH^-] = 1x10^-14

[OH^-] = 1x10^-14 / 5.62x10^-12

[OH^-] = 1.78x10^-3 M