Gargamel - 12-3-2013 at 05:07
If I put some hygroscopic salt like sodium- or ammonium nitrate in a container together with silica gel, which one will dehydrate the other at normal
atmospheric pressure?
The process of picking up water in silica gel is a different one than with salts.
Is there some way to compare silica gel with the critical relative humidity of a salt?
Endimion17 - 12-3-2013 at 06:04
Hygroscopic substances do not dehydrate, they merely shift the evaporation balance. Phosphorus(V) oxide shifts it greatly, while table salt
does it rather weakly.
Therefore it's impossible to have an outcome where you've got a sealed container and two substances, one completely dry and one stuffed with water it
sucked from the first one.
However, in this battle between ammonium nitrate and silica gel, I'm pretty sure the balance will be shifted towards the nitrate, especially sodium
nitrated.
I could check it in the literature, but I don't have the time at the moment.
Also, I'm sure someone posted a list of "strengths" of each desiccating agent on this forum somewhere.
jock88 - 12-3-2013 at 06:37
Humidity fixed points of binary saturated aqueous solutions
http://nvlpubs.nist.gov/nistpubs/jres/81A/jresv81An1p89_A1b....
that might help
google: creating fixed relative humidity with salts
[Edited on 12-3-2013 by jock88]
Gargamel - 17-3-2013 at 08:31
I'm not sure if I understand everything correctly.
Imagine the ambient humidity is below the critical point and the salt is dry. Will it still attract moisture?
When I raise the humidity slowly to the critical point, will the salt start to absorb water in the moment I reach the critical point or will it start
before?