Ammonia, nh3, is a weak base with a kb value of 1.8×10−5. part a what is the ph of a 0.440 m ammonia solution? express your answer numerically to two decimal places. view available hint(s)

Answer is: pH of ammonia solution is 11,43.
Chemical reaction of ammonia in water: NH₃ + H₂O → NH₄⁺ + OH⁻.
Kb(NH₃) = 1,8·10⁻⁵.
c₀(NH₃) = 0,44 M = 0,44 mol/L.
c(NH₄⁺) = c(OH⁻) = x.
c(NH₃) = 0,44 mol/L - x.
Kb = c(NH₄⁺) · c(OH⁻) / c(NH₃).
0,000018 = x² /  (0,4 mol/L - x). 

x²  + 0,000018x - 0,0000072 = 0.