A solution contains 0.0100 M Pb2 (aq) and 0.0100 M Sr2 (aq). If we add SO42–(aq), what will be the concentration of Pb2 (aq) when SrSO4(s) begins to precipitate?
Ksp of SrSO4 = 2.8*10^-7
Ksp of PbSO4 = 1.8*10^-8
SrSO4(s) ----------> Sr^2+ (aq) + SO4^2- (aq)
Ksp = [Sr^2+][SO4^2-]
2.8*10^-7 = 0.01[SO4^2-]
[SO4^2-] = 2.8*10^-7/0.01 =
2.8*10^-5 The value is just slightly greater than this then SrSO4
will precipitate
Ksp = [Pb^2+][SO4^2-]
1.8*10^-8 = [Pb^2+]*2.8*10^-5
[Pb^2+] = 1.8*10^-8/2.8*10^-5 = 6.43*10^-4M
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