Question

how much water would be needed to dissolve 5g of PbS? Ksp= 9.04*10^-29

Answer 1

PbS <----> Pb2+   +   S2-
                         S                 S

Ksp = [Pb2+] [S2-]
9.04*10^-29 = S*S
S = 9.51*10^-15 M

So for PbS to dissolve Concentration PbS should be 9.51*10^-15 M
number of moles of PbS = mass of PbS / molar mass of PbS
          = 5/239.3
          =0.0209 mol

use:
concentration = number of moles/ volume of water
9.51*10^-15 = 0.0209 / volume of water
volume of water = 2.2*10^12 L