Sciencemadness Discussion Board

Can nitric acid be blue?

chornedsnorkack - 15-7-2021 at 12:20

Or even as much as green?
NO2 is red/brown... on dilution, it turns light yellow, and on cooling it also pales as it dimerizes to N2O4.
N2O3, however, is bright blue as liquid and solid.
So the liquid solutions of NO2 (yellow) and N2O3 should be green.

But can N2O3 coexist with HNO3 in solution? Which way does the equilibrium of the reaction

Bedlasky - 15-7-2021 at 13:05

I work in lab and I work with samples of HNO3 of various concentrations and various purity. Some samples are green, but they usually didn't contain any NOx. I don't know why they are green, maybe it have something to do with iron contamination? HNO3 containing NO2 have yellow to orange colour. Even white fuming nitric acid have slight yellow tint due to presence of tiny amount of NO2 (and this concentration is very very low, the amount of NO2 can't be determined by manganometry).

I don't know how in conc. nitric acid, but in conc. sulfuric acid N2O3 dissotiates in to NO+, which is colourless. I can try to dissolve some NaNO2 in WFNA tommorow and see what happens.

Your green HNO3 is from chemical company or do you make it yourself?

Bedlasky - 16-7-2021 at 01:05

I tried today add some NaNO2 in to the 99% HNO3. Acid turned yellow, not blue or green.

[Edited on 16-7-2021 by Bedlasky]

Texium - 16-7-2021 at 05:36

N2O3 is only stable at very low temperatures.

metalresearcher - 16-7-2021 at 12:06

Probably contaminated with copper, which easily dissolves into Cu(NO3)2 ?

Antiswat - 18-7-2021 at 06:52

HNO2 is blue, let me see if i can find pics of a HNO2 reaction, or well more like turquoise. from reaction of NaNO3/NaNO2 + HCl + IPA

Bedlasky - 18-7-2021 at 09:38

I agree with metalresearcher. When you dissolve copper in azeotropic HNO3, solution turns to dark blue or even green.