General Chemistry Acids and Base Question

Question

What is the hydroxide ion concentration of a KOH solution that has a pH of 9.20?

Answer 1

pOH = 14 - pH

[OH^-] = 10^-pOH

1.58 x 10^-5 M

Answer 2

pH = 9.20

pOH = 14 - 9.20 = 4.80

[OH-] = 1x10^-4.80

[OH-] = 1.58x10^-5 M

Done a different way:

[H⁺] = 1x10^-9.20 = 6.31x10^-10 M

[H+][OH-] = 1x10^-14 = Kw

[OH-] = 1x10^-14/1/6.31x10^-10

[OH-] = 1.58x10^-5 M