Answer:
5.55 x 10⁻³ mol/L.
Explanation:
∵ pH + pOH = 14.
∴ pOH = 14 - pH = 14 - 10.50 = 3.5.
∵ pOH = - log[OH⁻].
∴ - log[OH⁻] = - 3.5.
∴ [OH⁻] = 3.16 X 10⁻⁴.
∵ [OH⁻] = √(kb)(c)
kb = 1.8 x 10⁻⁵.
c is the initial concentration.
3.16 X 10⁻⁴ = √(1.8 x 10⁻⁵)(c).
by squaring both sides:
(3.16 X 10⁻⁴)² = (1.8 x 10⁻⁵)(c).
1.0 x 10⁻⁷ = (1.8 x 10⁻⁵)(c)
∴ c = (1.0 x 10⁻⁷)/(1.8 x 10⁻⁵) = 5.55 x 10⁻³ mol/L.
