J={c.(Mg2+)}{c(OH)} =0.25×(9.5×104)2 =2.3×107 Kf(Mg(OH)2)=5.1X1012 J>Ko, Mg(OH)will precipitate. (2)In order to prevent Mg(OH)2 from precipitating out of the solution Two methods! 7 4 2 2 2 o 2.3 1 0 0.2 5 (9.5 1 0 ) { (M g )}{ (O H ) } - - + - =  =   J = c c 12 (Mg(OH)2 ) =5.1×10- Ksp ， will precipitate. Mg(OH)2 J > K sp (2) In order to prevent Mg(OH)2 from precipitating out of the solution Two methods!