How to calculate the pH of NH4OH (0.1M)

Answer is: pH of ammonium hydroxide is 11.13.

Chemical reaction of ammonium hydroxide in water: NH₄OH → NH₄⁺ + OH⁻.

Kb (NH₄OH) = 1,8·10⁻⁵.

c ₀ (NH₄OH) = 0.1 M.

c (NH ₄⁺) = c (OH⁻) = x.

c (NH₄OH) = 0.1 M - x.

Kb = c (NH ₄⁺) · c (OH⁻) / c (NH₄OH).

0,000018 = x² / 0.1 mol/L - x.

Solve quadratic equation: x = c (OH⁻) = 0.00133 M.

pOH = - logc (OH⁻).

pOH = 2.87.

pH = 14 - 2.87.

pH = 11.13.