What Sulfate Concentration Initiates Precipitation in a Mixed Nitrate Solution?

[jpd5184]

Homework Statement

consider a solution that initially contains 0.15M Sr(NO3)2 and 0.25M Ba(NO3)2. The sulfate ion concentration is gradually increased by the slow addition of solid Na2SO4.
a. What is the sulfate ion concentration when barium sulfate just begins to precipitate
b. what is the sulfate concentration when strontium sulfate just begins to precipitate

Homework Equations

a. Ba(NO3)2 ---- Ba^2+ + 2NO3-
Ksp=[NO3-][Ba^2+]
Qsp=[NO3-][Ba^2+] (initial concentrations)
b. Sr(NO3)2 ---- Sr^2+ + NO3-
ksp=[NO3-][Sr^2+]
Qsp=[NO3-][Sr^2+] (initial concentrations)

The Attempt at a Solution

knowing the ksp for each i can solve the equations for the unknown

 

[Borek]

Something wrong either with the wording or with your understanding of the problem. Nitrates don't precipitate, sulfates do.

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[jpd5184]

i changed the problem. this is what it should be but doesn't make sense since their is no sulfate in the problem

 

[chemisttree]

Ignore the nitrate ions. They are spectators in this process, only there to provide a countercharge to the Sr and Ba. Given the known [Sr] and [Ba], how much sulfate (read that as [SO4-2]) do you need to add to reach Ksp for SrSO4 and BaSO4?