Bob the scientist has a 100 mL solutin that contains 0.03 moles of each Pb2+ and Sr2+. Using selective precipitation, what is the concentration of CO3 2- you can add to the solution to separate the two metals? Solution Ksp PbCO3 = 1.6 x 10^-13 Ksp SrCO3 = 1.3 x 10^-9 PbCO3 with lower Ksp would precipitate first from the solution [Pb2+] = 0.03 mol/0.1 L = 0.3 M [Sr2+] = 0.03 mol/0.1 L = 0.3 M [CO3^2-] needed to precipitate PbCO3 = Ksp/[Pb2+] = 1.3 x 10^-13/0.3 = 4.33 x 10^-13 M All of PbCO3 is precipitates out first. [CO3^2-] needed to precipitate SrCO3 = Ksp/[Sr2+] = 1.3 x 10^-9/0.3 = 4.33 x 10^-9 M Then SrCO3 is precipitates by using higher concentration of CO3^2-. .

1. Bob the scientist has a 100 mL solutin that contains 0.03 moles of each Pb2+ and Sr2+. Using
selective precipitation, what is the concentration of CO3 2- you can add to the solution to
separate the two metals?
Solution
Ksp PbCO3 = 1.6 x 10^-13
Ksp SrCO3 = 1.3 x 10^-9
PbCO3 with lower Ksp would precipitate first from the solution
[Pb2+] = 0.03 mol/0.1 L = 0.3 M
[Sr2+] = 0.03 mol/0.1 L = 0.3 M
[CO3^2-] needed to precipitate PbCO3 = Ksp/[Pb2+]
= 1.3 x 10^-13/0.3 = 4.33 x 10^-13 M
All of PbCO3 is precipitates out first.
[CO3^2-] needed to precipitate SrCO3 = Ksp/[Sr2+]
= 1.3 x 10^-9/0.3 = 4.33 x 10^-9 M
Then SrCO3 is precipitates by using higher concentration of CO3^2-.