Chromate and dichromate anions has the following equilibrium in acidic solution:

$$\ce{2CrO4^2- + 2H3O+ <=> Cr2O7^2- + 3H2O}$$

How can one experimentally measure the concentration of each ion at a certain equilibrium?

  • $\begingroup$ pH indicators come to mind. More elaborate techniques could include conductivity measurements, NMR measurements, density measurements, etc. $\endgroup$
    – Curt F.
    Commented Feb 1, 2016 at 5:16
  • $\begingroup$ Surely the simplest way is UV-vis spectroscopy, unless the peaks overlap significantly. $\endgroup$ Commented Feb 1, 2016 at 8:59
  • $\begingroup$ certainly don't try spectrophotometry, I did that in an experiment and my results were atrocious, and this is the main reason why I am asking. The difference in peak wavelengths was about 5nm $\endgroup$
    – user289661
    Commented Feb 2, 2016 at 4:53
  • $\begingroup$ O17 NMR seems to be a thing and should work. Cr53... possibly two, but unclear. However at elevated temperature chromate/bichromate conversion may become too fast for distinguishable peaks to exist. $\endgroup$
    – permeakra
    Commented Feb 2, 2016 at 14:43


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