# How to calculate the gas-liquid interaction for dissolved HNO3 in water with air?

Thanks for reading this and (maybe) helping me in advance!

I have to face the following problem: I have got $\ce{HNO3}$ dissolved in water (roughly $\pu{50\%}$) and I want to know how much $\ce{HNO3}$ will be in the air directly above it. I got classes about liquid-gas phases, but it was a long time ago and therefore I am not capable anymore to engage such a question.

As far as I can recall the pressure and temperature are important, which are $\pu{1 atm}$ and $\pu{20-25^oC}$ (but I want to calculate it for a range between $\pu{20-100^oC}$). I can imagine that it might be hard due to the fact that a part of the $\ce{HNO3}$ will split into ions $\ce{H+}$ and $\ce{NO3-}$ (till it reach its pKa), so that will give an equilibrium towards the liquid phase. But in the end there must be some $\ce{HNO3}$ in the air due to gas-liquid equilibrium.

Is there anyone that can tell me how to calculate this or how to engage this question? Any advice is appreciated!

Edit: During further investigation I found out that the problem is even more complicated since $\ce{HNO3}$ will split into $\ce{NO}$, $\ce{NO2}$ and $\ce{N2O4}$ (nitrous gases). If possible I want all the concentrations of these gases at those temperatures.

• I think you could treat the effect of decomposition as negligible for such temp. and conc. but it still wouldn't do you much good if you don't have software like aspen or sth. – Mithoron Apr 5 '17 at 22:14
• Thank you for your reply! (sorry for the late response) I might do it with Aspen then, since there is nearly no tutorial how to deal with this without software. But as far as I know HNO3 decomposes allready at room temperature. The NO2 will desolve almost immediately and the O2 and H2O will be gone of course. But NO2 will not go further into NO and N2O4 according to you? And about Aspen; Aspen doesn't have chemical reactions in its database right? So how does Aspen encouter the decomposition of the nitric acid? – D. Nijland Apr 13 '17 at 7:01