.6M NH4OH & 1.5M NH4Cl. What's max Conc of Mg+2 present w/out precip Mg(OH)2 KSP=MgOH2=9x10^-12 NH4=1.8x10^-5

Answer 1

The ammonium hydroxide and ammonium chloride form a buffer mix, which governs the pH and, by water Kw, [OH]. If [Mg]x[OH]^2 =Ksp or more, ppt will occur.

[NH4+][OH-]/[NH3] = 1.8x10-5
We can assume that dissociation of NH4OH adds little NH4+ compared to that which is provided by NH4Cl, so [1.5][OH-]/[0.6] = 1.8x10-5
Then [OH-]= 7.2x10-6
By arguement above, [Mg+2][7.2x10-6]^2=Ksp
[Mg+2]= appx 9 x10-12 / 52 x 10-12 = 0.18 appx