mass of Co(NO₃)₂ = 1.95 g V KOH = 0.350 L [KOH] = 0.220 M Kf = 5.0 x 10⁹ molar mass of Co(NO₃)₂ = 182.943 g/mol so [Co(NO₃)₂] = 1.95 / (0.350 * 182.943) = 0.03045 M [Co²⁺] = 0.03045 M [OH⁻] = 0.22 M chemical reaction: Co²⁺(aq) + 4 OH⁻ ⇄ Co(OH)₄²⁻ I (M) 0.03045 0.22 0 C (M) - 0.03045 - 4 (0.03045) 0.03045 E (M) - x 0.22 - 4(0.03045) 0.03045 = 0.0982 Kf = [Co(OH)₄²⁻] / [Co⁺²][OH⁻]⁴ 5.0 x 10⁹ = (0.03045) / x (0.0982)⁴ x = 6.5489 x 10⁻⁸ at equilibrium: [Co²⁺] = 6.54 x 10⁻⁸ [OH⁻] = 0.0982 M [Co(OH)₄²⁻] = 0.03045 M
