[mormegil]

Hello

What is a possible reaction path between a mixture of gaseous nitogen dioxide in synthetic air and bromocresole purple. The synthetic air have relative humidity RH=7%.

Best Regards

Cuma

[Arkcon]

OK, what sort of reactions are you expecting?  Try to solve this one by removing jargon, and reducing it to chemical reactions.  What are the possible reactants in the mixture known as synthetic air?   What do you expect is the sorts of reactions you can get with bromocresole purple?  Usually, its pretty difficult to predict products from reactants.  But in this case, there are some pretty typical ways for the reactions to go?

[mormegil]

An exposition of the bromocresole purple BP to the NO2 in air changes the position of absorption band. The wavelength of maximum absorbance is shifted  from ~430 nm to ~530 nm - BP changes its colour. A reversibility of the ongoing reaction is rather poor. I am expecting that NO2 molecule is incorporated to the BP. The synthetic air is composed of nitrogen, oxygen and water vapour. What are these typical ways?

Best regards

Cuma

[Arkcon]

Interesting.  But not what I was thinking.  If you look up: bromocresole purple, in any general resource, what is it called?

[vmelkon]

They probably suggest the 7% humidity to suggest that NO2 could or will react with it and make HNO3.