# What are the methods used to measure the concentrations of these anions?

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?

• pH indicators come to mind. More elaborate techniques could include conductivity measurements, NMR measurements, density measurements, etc. – Curt F. Feb 1 '16 at 5:16
• Surely the simplest way is UV-vis spectroscopy, unless the peaks overlap significantly. – orthocresol Feb 1 '16 at 8:59
• 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 – user289661 Feb 2 '16 at 4:53
• 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. – permeakra Feb 2 '16 at 14:43