What Sulfate Concentration Initiates Precipitation in a Mixed Nitrate Solution?

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Discussion Overview

The discussion revolves around determining the sulfate ion concentration required to initiate precipitation of barium sulfate and strontium sulfate in a mixed nitrate solution. The context includes a homework problem involving the solubility product constants (Ksp) of the respective sulfates and the role of nitrate ions as spectator ions.

Discussion Character

  • Homework-related, Technical explanation

Main Points Raised

  • One participant presents a homework problem involving the concentrations of Sr(NO3)2 and Ba(NO3)2 and asks for the sulfate concentrations at which precipitation occurs.
  • Another participant suggests there may be an issue with the problem's wording or understanding, noting that nitrates do not precipitate while sulfates do.
  • A third participant indicates a change in the problem but expresses confusion due to the absence of sulfate in the original problem statement.
  • A later reply emphasizes that nitrate ions should be considered spectators and suggests focusing on how much sulfate is needed to reach the Ksp for both SrSO4 and BaSO4.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the clarity of the problem statement or the role of nitrate ions, indicating some disagreement and confusion regarding the initial conditions and the approach to the problem.

Contextual Notes

The discussion highlights the dependence on the definitions of ions involved and the assumptions regarding the role of nitrate ions in the precipitation process. There are unresolved aspects regarding the initial sulfate concentration and its relation to the Ksp values.

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

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

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