How Would You Precipitate BaCrO4 from Ba(NO3)2 and K2Cr2O7 Solutions?

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Discussion Overview

The discussion revolves around the process of precipitating barium chromate (BaCrO4) from a solution containing barium nitrate (Ba(NO3)2) and potassium dichromate (K2Cr2O7). Participants explore the chemical equilibria involved and the conditions necessary for precipitation, including the role of pH and ion concentrations.

Discussion Character

  • Homework-related
  • Exploratory
  • Technical explanation

Main Points Raised

  • One participant seeks guidance on how to approach the problem and expresses uncertainty about the starting point.
  • Another participant suggests applying knowledge from a related discussion on chromate-dichromate equilibrium to the current problem.
  • A question is raised about the concentration of CrO42- needed for precipitation and its dependence on pH.
  • A participant proposes that a high concentration of CrO42- is necessary for precipitation and suggests using NaOH to lower H+ concentration, thus shifting the equilibrium towards CrO42- formation.
  • The same participant notes that adding Ba(NO3)2 would lead to the formation of BaCrO4, while BaCr2O7 is more soluble, implying a preference for BaCrO4 precipitation.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and confidence regarding the chemical principles involved, but there is no clear consensus on the best approach or the specifics of the precipitation process.

Contextual Notes

Participants reference the chromate-dichromate equilibrium and its implications for the precipitation process, but the discussion does not resolve the exact conditions or concentrations required for successful precipitation.

Paulham
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Homework Statement


Hi everyone,

I'm trying to finish my lab report but I'm stuck on this question and don't even know how to start it. Could anyone let me know how to board it or a starting clue?

I'm given these two equations

1. BaCrO4 (s) <---> Ba2+ (aq) + CrO42- (aq)

2. 2CrO42- (aq) + 2H+ (aq) <----> Cr2O72- (aq) + H2O (l)

Question: How would you precipitate BaCrO4 from a solution of Ba(NO3)2 and K2Cr2O7 ? And I need to show it in chemical equations.

Homework Equations

The Attempt at a Solution



I honestly have no clue...
 
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You're working on the chromate-dichromate equilibrium in another thread; can you apply that equilibrium to this problem?
 
Sure, if I knew how to that is...:)
 
Do you need low, or high concentration of CrO42- to precipitate BaCrO4?

How does concentration of CrO42- depend on pH? (That's a direct conclusion of the question you posted in another thread, changing pH shifts the CrO42-/Cr2O72- equilibrium; how?)
 
Hi,

I was just looking at that and this is what I came up with: so I would need a high concentration of CrO42- to precipitate BaCrO4 and I can increase the concentration of CrO42- by lowering the concentration of H+ by adding NaOH so it will neutralize the H+. This way my equilibrium will shift to the left forming more CrO42-. Then by adding Ba(NO3)2...the NO3 would be a spectator ion but Ba2+ would form the BaCrO4 precipitate because BaCr2O7 is more soluble...would that be right?
 
Paulham said:
...would that be right?
It would.
 

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