What is the concentration of hydroxide ion in household ammonia, an aqueous solution of nh3 that has a ph of 11.50?

The concentration of hydroxide ion in household of ammonia that has a ph of 11.50 is calculated as follows

as we well know Ph + POh = 14

POh is therefore=14 - 11.50 = 2.5

POh is calculated as follows

POh = - log (-OH) = 2.5

-OH concentration is therefore = 10^-2.5 = 3.162 x10^-3