Answer:
pOH = 3.18
Explanation:
The equilibrium of a weak base as NX3 is:
NX3(aq) + H2O(l) ⇄ HNX3⁺(aq) + OH-(aq)
Where the equilibrium constant, Kb, is:
Kb = 2.5x10⁻⁶ = [HNX3⁺] [OH-] / [NX3]
As both HNX3⁺ and OH- ions comes from the same equilibrium, their concentrations are the same, that is:
[HNX3⁺] = X
[OH-] = X
And: [NX3] = 0.175M:
2.5x10⁻⁶ = [X] [X] / [0.175M]
4.375x10⁻⁷ = X²
X = 6.61x10⁻⁴M = [OH-]
As pOH = -log [OH-]
