# How to identify the concentration of nitric acid?

I have quite a small quantity of concentrated nitric acid I had acquired about two years ago. This was given to me by a friend in a couple of Pyrex volumetric flasks with stopper and some in a borosilicate reagent bottles. The acid does have a whiskey brown color now.

Is there any simple method or visual cue to identify what concentration the nitric acid could be with a simple test? I want to see if the acid is 70% nitric acid. If it's the higher concentration of 90%, then I want to dilute it to 70%. I have attached a picture of one of the bottles for reference to see the color below.

• Simply put, if you've had it for years, it can't be 90%. Mar 11 '21 at 21:34
• For starters it would be fuming nitric acid. Why do you even think there could be sth stronger then usual conc. acid? Mar 11 '21 at 22:24
• @IvanNeretin I agree the concentration may have been lost a bit overtime. But it’s still from late 2018. Mar 11 '21 at 22:38
• @Mithoron I actually wanted some 70% acid. The reason I wanted to to know if there is any visual way or simple test to check concentration is because I haven’t really dealt with concentration nitric much. Only sulfuric and HCl. Become of the change in color from clear I was a bit confused if this is the 70% or 90%+ conc. Mar 11 '21 at 22:41
• $\ce{4 HNO3 -> 2 H2O + 4 NO2 + O2}$ If it's dark, there's plenty of nitrogen dioxide. Concentrated nitric acid should be clear. Btw. This does not look like a safe storage container. Mar 11 '21 at 22:46