posted by Jo .
Use Ksp to find the concentration of an ion in a saturated solution. Consider a 2.50E-3 M solution of Al2(SO4)3.
(a) What [OH^-] is required to initiate precipitation of Al^3+ from the solution?
(b) What [OH^-] is required to lower the [Al^3+] to 2.00E-7 M ?
2.5E-3M Al2(SO4)3 ==> 2Al^3+ + 3SO4^=
Look up Ksp for Al(OH)3.
Ksp = (Al^3+)(OH^-)^3
Substitute Ksp and 2.5E-3 and solve for OH^- for part A.
b. I assume this is a different problem and the Al is as quoted in part b and has nothing to do with part a.
Substitute for Ksp ad 2E-7 and solve for OH^-