Question

What is the OH- concentration of a solution whose pH is 12.40?

Answer 1

pH + pOH = pKw = 14

12.40 + pOH = 14

pOH = 14 - 12.40

pOH = 1.6

[OH⁻] = $10 ^{-pOH}$

[OH⁻] = $10 ^{-1.6}$

[OH⁻] = 2.5x10⁻² M

hope this helps!