Headspace Concentration calculation 2

[Vastorm]

I have a headspace calculation problem that is very long. To start I can't find the method to determine the concentration of the headspace of a vessel containing a liquid such as ammonia. I know the molecular weight, vapor pressure, ambient temp, volume of cylinder, and all of that stuff, but cannot find the method to calculate the vapor concentration of a closed vessel that is allowed to reach equilibrium. So in short how do I calculate the concentration of the space above a liquid in a cylinder sitting on a lab counter?

 

[Latexman]

If it's ammonia and water, you can look those up in Perry's. They have aqueous ammonia equilibrium data.

Is this homework?

Good luck,
Latexman

 

[Homayun]

the definition of "Concentraion" is number of Moles of a component divided by volume of interest. Now, I hope you can figure out the volume above your liquid level! That should be easy. To start with, you may want to ignore the volume in the head.
Now, for the number of moles in the vapor space, I guess you can use Henry's law. If you know the partial pressure of Amonia on top of the cylinder, then you can calculate the number of moles from the ideal gas law n=PV/RT. You know the P (from Henry law), you know the v (volume) and R and T.

I hope this helps buddy..

 

[Vastorm]

Thanks a lot for the help. This is not homework, this is a real problem. I can easily make the cylinder whatever volume I wish, so I could have glass blower make a 1.1L vessel and put 0.1L of liquid in the bottom for ease of calculations. It is 28% ammonia and water so I'll try looking it up. Thanks again for the help. This is only the tip of the iceberg ).

 

[Latexman]

OK, just remember ammonia and water are highly non-ideal (mainly hydrogen bonding), so Raoult's Law will not be very accurate. Actual data is best. If you want to model it, you'll need a good liquid activity coefficient model for the ammonia and water binary pair.

Good luck,
Latexman