# Chemical Equlibrium of BaCrO4

1. Feb 9, 2015

### Paulham

1. The problem statement, all variables and given/known data
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.

2. Relevant equations

3. The attempt at a solution

I honestly have no clue...

2. Feb 9, 2015

### Bystander

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

3. Feb 9, 2015

### Paulham

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

4. Feb 10, 2015

### Staff: Mentor

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?)

5. Feb 10, 2015

### Paulham

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?

6. Feb 10, 2015

It would.