A solution is initially 0.10m in mg2 + (aq) and 0.10m in fe2 + (aq). solid naoh is slowly added. what is the concentration of fe2 + when mg (oh) 2 first precipitates? ksp (mg (oh) 2) = 6.0 x 10-10; ksp (fe (oh) 2) = 7.9 x 10-16

Mg (OH) ₂ ⇄ Mg²⁺ + 2 OH⁻

Ksp = [Mg²⁺] [OH⁻]²

6.0 x 10⁻¹⁰ = 0.10 x [OH⁻]²

[OH⁻] = 7.746 x 10⁻⁵ M

when Mg (OH) ₂ 1st precipitates, [OH⁻] = 7.746 * 10⁻⁵ M

Fe (OH) ₂ Fe²⁺ + 2OH⁻

Ksp = [Fe²⁺] [OH⁻]²

7.9 x 10⁻¹⁶ = [Fe²⁺] x (7.746 x 10⁻⁵) ²

[Fe²⁺] = 1.32 x 10⁻⁷ M

Answer: 1.32 x 10⁻⁷ M