I am trying to calculate what the vapor concentration of HCN will be in an atmospheric tank. The tank consists of water with an HCN concentration of 90 ppm. I know the temperature that the tank will be operating at. It is probably important to note that this tank is not going to be in service (no pumping into or out of). I calculated the vapor pressure of HCN at the given temperature. So now I have concentration in the liquid phase, operating pressure, and the vapor pressure. Should I use Raoult's Law to find the HCN vapor concentration in ppm? Or can I not assume ideal? I know this is extremely basic, but I am having a complete brain block, it has been a long day. Thank you in advance!