1. A solution is 0.25 M in each of the cations Ba+2 and Ca+2.
a) What concentration of CrO4-2 is needed to precipitate as much Ba+2 as possible without precipitating the Ca+2? (BaCrO4:Ksp=2.1x10^-10; CaCrO4:Ksp=7.1x10^-4)
b) Remember the concentration of CrO4-2 depends on the acidity of the solution and is governed by the equilibrium:
Cr2O7-2(aq) + 3H2O(l) <--> 2CrO4-2(aq) +2H3O+(aq) K=2.5x10^-15
In a 0.25M solution of K2Cr2O7, what pH will give the equilibrium concentration of CrO4-2 calculated above?