Hygroscopicity ?

[Hal.]

What is the most hygroscopic material in an ordinary household ?

[insane_alien]

silica gel in dessicant sachets usually.

[mississippichem]

Silica gel or the calcium chloride that is present in some swimming pool "chlorine tabs".

[Hal.]

And how does water itself rate ? Can it soak up water ?

[johnheritage]

http://en.wikipedia.org/wiki/Hygroscopy

[CaptainPanic]

And how does water itself rate ? Can it soak up water ?

Liquid water is usually in equilibrium with the water vapor. And the amount of vapor depends on the temperature (the vapor pressure is a function of the temperature).

 

Hygroscopic materials can 'suck' water out of the gas phase (air), and the water in the gas phase will then be at a lower concentration than the equilibrium concentration.

 

Since water itself cannot make the water concentration in the gas phase go below its equilibrium concentration, water cannot be considered hygroscopic.

[Hal.]

Is Hygroscopicity just one example of a general phenomena where different materials can take other materials from the Air ?

 

For example , there is Argon in the Air . Would this general phenomena be seen in the case of Argon by using materials which can take Argon from the Air and if so , what is the name of the general phenomena ?

[CaptainPanic]

Is Hygroscopicity just one example of a general phenomena where different materials can take other materials from the Air ?

 

For example , there is Argon in the Air . Would this general phenomena be seen in the case of Argon by using materials which can take Argon from the Air and if so , what is the name of the general phenomena ?

 

There are many names for it... in general you can say that the materials try to be in equilibrium. Such equilibriums are everywhere. And nature always tries to move something towards the equilibrium if it's not in equilibrium yet.

 

Generally, if you have bulk material A (let's say air) and bulk material B (something else)... and then another material C, which is present in one of the two... there will be an equilibrium where material C distributes itself over materials A and B in some way. (Nearly) all the material C can go in the air, or it can go into the material B, or it can be 50-50, or anything in between.

 

If you use a liquid to remove something from a gas, it can be called absorption.

If you use a gas to remove something from a liquid, it can be called stripping.

If you use a solid to remove something from liquid or gas, and the material C would go onto the surface of the solid rather than into it, it's called adsorption (note, adsorption, and absorption are not the same!).

If you use a liquid to remove something from another liquid or solid, it's called extraction.

[Hal.]

This thread has answered all I wanted to enquire of , thanks to all , hygroscopicity is very interesting !

[pippo]

Well, Im a little late, but you may be curious on some compounds that I have worked with as being hygroscopic:

Of course, CaCl2 has been mentioned. cheap and safe

Concentrated sulfuric acid- quite dangerous/not available to consumer market

Magnesium chloride 6XH2O- expensive, safe

Lithium compounds- chloride/bromide, hard to get

Mercuric chloride/nitrate- expensive, TOXIC

 

just a few......