pH solution Question

Question

What is the pH of a solution that has a hydroxide ion concentration of 1.0 x 10^-2 M?

Answer 1

An alternative way is to first calculate the pOH using the equation,

pOH = - log [OH^-] = - log 1.0 x 10^-2 = 2.00

The pH and pOH are related by the equation, pH + pOH = 14.00. Since we know the pOH, the pH can then be calculated.

pH = 14.00 - pOH = 14.00 - 2.00 = 12.00

Answer 2

We need to determine the [H⁺]. Since [H⁺][OH^-]=1.0x10^-14 (the Kw for water), [H⁺]=1.0x10^-14/[OH^-], or in this problem [H⁺]=1.0x10^-14/1.0x10^-2 or 1.0x10^-12. Since pH=-log [H⁺], pH=-log 1.0x10^-12=12. The pH is 12, very basic and consistent with the high concentration of [H⁺].