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

[Paulham]

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) + CrO₄^2- (aq)

2. 2CrO₄^2- (aq) + 2H+ (aq) <----> Cr₂O₇^2- (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...

 

[Bystander]

You're working on the chromate-dichromate equilibrium in another thread; can you apply that equilibrium to this problem?

 

[Paulham]

Sure, if I knew how to that is...:)

 

[Borek]

Do you need low, or high concentration of CrO₄^2- to precipitate BaCrO₄?

How does concentration of CrO₄^2- depend on pH? (That's a direct conclusion of the question you posted in another thread, changing pH shifts the CrO₄^2-/Cr₂O₇^2- equilibrium; how?)

 

[Paulham]

Hi,

I was just looking at that and this is what I came up with: so I would need a high concentration of CrO₄^2- to precipitate BaCrO₄ and I can increase the concentration of CrO₄^2- 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 CrO₄^2-. 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?

 

[Bystander]

...would that be right?

It would.