Acid base and pH

Question

A solution has [H+] = 1.5 × 10 ^−7 M. What is the [OH−] in this solution?

Answer 1

[H⁺][OH^-] = Kw = 1x10^-14 (memorize this relationship)

(1.5x10^-7)(OH^-) = 1x10^-14

[OH^-] = 1x10^-14/1.5x10^-7

[OH^-] = 6.7x10^-8 M