How to measure the volatiliy of a liquid?

[sector6]

Does anyone know what property of a liquid is directly proportional to the volatiliy? I suspect that the specific gravity does since higher the density -> higher sp. gravity -> lower volatility.

 

Looking from at the molecules again to try to explain (chemistry realm!): Larger molecules -> higher attractive forces between the molcules (Van der Waal) -> higher density and higher sp. gravity >>>>>>>>>>>>>> The chemical is less volatile.

Edited April 8, 2016 by sector6

[Enthalpy]

It's a matter of boiling point, not density.

 

The boiling point relates with the molecule size, but isn't completely linked, since functional groups like hydroxyls increase the intermolecular forces much more than -CH₂- do for instance. Comare water with propane.

 

The density neither relates simply with the molecule size nor the intermolecular forces. It's in the first line a matter of constituent atoms.

[swansont]

Does anyone know what property of a liquid is directly proportional to the volatiliy? I suspect that the specific gravity does since higher the density -> higher sp. gravity -> lower volatility.

 

Looking from at the molecules again to try to explain (chemistry realm!): Larger molecules -> higher attractive forces between the molcules (Van der Waal) -> higher density and higher sp. gravity >>>>>>>>>>>>>> The chemical is less volatile.

 

 

Density has two components — how many atoms you can pack into a volume and the mass of those atoms. While the former might have some correlation to volatility, the latter does not. Mercury has a fairly high density, mainly because its atomic number is 80, but it also has a higher vapor pressure (~2 mTorr) and lower boiling point (357 ºC) than many of the elements with smaller densities.

[sector6]

@enthalpy, swansont: thank you for pointing out my misconceptions if u have any queries on biomolecular engineering, proteins and polymers, I might be able to help

[John Cuthber]

It's complicated.

Boiling point is a good clue, but most of the time you are not talking about a material near to its boiling point.

So you need to also know how the vapour pressure varies with temperature.

You can get a reasonable approximation for that from this sort of thing

https://en.wikipedia.org/wiki/Clausius%E2%80%93Clapeyron_relation

 

If you know the vapour pressure and the heat of evaporation then you can get an idea of which of two solvents is likely to be more volatile.

In essence for things like making paint or varnish, they compare evaporation rate empirically.

.

http://marron-co.com/marron/PAINT%20STANDARD/ASTM%20%20PAINTS/0601/D3539.pdf

[sector6]

@john c., thanks for ur input. The Clausius-Clapeyron rang some rusty old bell in the memory lane I'll see what else I could find on this....research time (i.e. googling time)

[sector6]

It's complicated.

Boiling point is a good clue, but most of the time you are not talking about a material near to its boiling point.

So you need to also know how the vapour pressure varies with temperature.

You can get a reasonable approximation for that from this sort of thing

https://en.wikipedia.org/wiki/Clausius%E2%80%93Clapeyron_relation

 

If you know the vapour pressure and the heat of evaporation then you can get an idea of which of two solvents is likely to be more volatile.

In essence for things like making paint or varnish, they compare evaporation rate empirically.

.

http://marron-co.com/marron/PAINT%20STANDARD/ASTM%20%20PAINTS/0601/D3539.pdf

@john cuthber: Didn't know they had an instrument called an evaporator! I think I'll be using a poor-man's version by using a mass balance every few hours