Possibility and detection of this chemical equilibrium

[24forChromium]

Dissolve a salt containingCr₂O₇^2- and an "inert cation" in water, would the following equilibrium occur in appreciable quantity?

Cr₂O₇^2-+OH^-⇔2CrO₄^2-+H⁺

If it does occur, I suppose the acidity of the water would affect the equilibrium constant (or at least the relative concentration of the Chromium-containing anion). In this case, would it be possible to determine the concentration of each anion with a spectrometer?

 

[DrDu]

The equilibrium certainly is important and pH dependent, as you say. It is used to separate Ba and Sr in chemical analysis, as BaCrO4 is less soluble than SrCrO4 and will form even in acidic solutions. It should be possible to follow the equilibrium spectroscopically.

 

[24forChromium]

The equilibrium certainly is important and pH dependent, as you say. It is used to separate Ba and Sr in chemical analysis, as BaCrO4 is less soluble than SrCrO4 and will form even in acidic solutions. It should be possible to follow the equilibrium spectroscopically.

thank you for your reply, I would like to confirm just one more thing, that is an equilibrium can be established simply by adding sodium chromate into water and both chromate and dichromate ions would be produced. Is that true? Or is is a certain amount of hydronium and hydroxide ions required?

 

[DrDu]

Wikipedia has quite some information on this:
https://en.wikipedia.org/wiki/Chromate_and_dichromate

This page
http://www.chemieunterricht.de/dc2/mwg/g-chroma.htm
also has a value for the equilibrium constant, so that you can calculate the ratio of the concentrations of chromate and dichromate in dependence on concentration and pH yourself.

 

[epenguin]

Yes we had a thread and some calculations about this system here. https://www.physicsforums.com/posts/3638905/