Asolution contains 0.10 m pb2+ and 0.10 m cu2.. which cation will precipitate first when a solution of nazs is slowly added to the mixture? refer to the information sheet for solubility constants. p a) pb2+ b) cu2+ c) impossible to tell d) both cations

b) Cu2+

Explanation:

Ksp PbS = 3.4 E-28

Ksp CuS = 6.0 E-37

∴ Ksp = 3.4 E-28 = [ Pb2+ ] * [ S2- ]

∴ [ Pb2+ ] = 0.10 M

⇒ [ S2- ] = 3.4 E-28 / 0.10 = 3.4 E-27 M

∴ Ksp = 6.0 E-37 = [ Cu2+ ] * [ S2- ]

∴ [ Cu2+ ] = 0.10 M

⇒ [ S2- ] = 6.0 E-37 / 0.10 = 6.0 E-36 M

we have:

(1) [ S2- ] PbS >> [ S2- ] CuS

(2) Ksp PbS >> Ksp CuS

from (1) and (2) it can determined, that separation can be carried out and also the cation that precipitates first is the Cu2+