What hydroxide concentration is required to

(a) Initiate precipitation of Ag2CrO4 from a solution that is 2.12 x 10^-3 M in Ag+?
(b) lower the Al^3+ concentration in the foregoing solution to 1.00 x 10^-9

2 answers

How did Al^+3 get in that solution and what does it have to do with the problem?
Sorry it was
(a) initiate precipitation of Al^3+ from a 5.00 x 10^-3 M solution of Al2(SO4)3?
(b) lower the Al^3+ concentration in the foregoing solution to 1.00 x 10^-9 M?