Question

The equilibrium concentration of aluminum ion in a saturated aluminum phosphate solution is
M.

Answer 1

You need to look up the Ksp for AlPO4.
......................AlPO4 ==> Al^3+ + PO4^3-
I.......................solid.....................0..............0
C.......................-x........................x..............x
E.......................solid.....................x..............x
Ksp = (Al^3+)(PO4^3-)
Substitute the E line into the Ksp expression and solve for x which will give you the (AlPO4) in mols/L for a saturated solution. (Al^3+) will be 3 times that. Post your work if you get stuck.