Physics Forums

Physics Forums (http://www.physicsforums.com/index.php)
-   Chemistry (http://www.physicsforums.com/forumdisplay.php?f=83)
-   -   Difference between crystallization and vaporization? (http://www.physicsforums.com/showthread.php?t=67638)

lwymarie Mar17-05 09:47 AM

difference between crystallization and vaporization?
 
If a solution is heated to dryness, a powder will be left. But under evaporation, a crystal will form. So what's the difference between crystallization and vaporization? How is the process of crystallization?

Are all the opaque (or milky) solutions contain a precipitate? And why some liquids are obpaque while some are transparent?

Here is a beaker. Inside is some oil on top of water. If the water is heated, so it becomes less thick and thus less dense, will it has a density lower than oil and so flow on the oil?

What is the general definition of a 'salt'?

-thx-

chem_tr Mar17-05 01:35 PM

Hello

I will try to answer your questions briefly.

Quote:

Quote by lwymarie
If a solution is heated to dryness, a powder will be left. But under evaporation, a crystal will form. So what's the difference between crystallization and vaporization? How is the process of crystallization?

Well, the difference is that the first will form amorphous materials, while the second one will be crystalline. In order to obtain good quality crystals, you should boil the solution until a clear solution is obtained, then let it cool unattended, in ambient temperature. Crystals will form, since you give enough time to allow solid phase formation. Amorphous materials occur instantly, they don't have much time to facilitate crystallization.

Quote:

Are all the opaque (or milky) solutions contain a precipitate? And why some liquids are obpaque while some are transparent?
They are rather called suspensions, and if you allow some time, a process known as "sedimentation" will occur, that is, the upper liquid becomes clear, and the insoluble solid precipitates to the bottom of the flask. Opaque liquids have some insoluble material, so they are suspensions or emulsions, depending on the physical state of the insoluble material.

Quote:

Here is a beaker. Inside is some oil on top of water. If the water is heated, so it becomes less thick and thus less dense, will it has a density lower than oil and so flow on the oil?
I think the solubility of oil increases with increasing temperature, so the layer becomes thinner. I don't think that densities would change greatly with a simple heating process.

Quote:

What is the general definition of a 'salt'?
A salt is basicly a compound, formed between a base and and acid. The anion of the salt comes from the acid, while the cation is from the base.

Borek Mar17-05 05:44 PM

Quote:

Quote by lwymarie
If a solution is heated to dryness, a powder will be left. But under evaporation, a crystal will form. So what's the difference between crystallization and vaporization? How is the process of crystallization?

IMHO the question is faulty - if you heat NaCl solution to dryness crystals will form. They will be smaller and not so nice, but they will form.

Quote:

Are all the opaque (or milky) solutions contain a precipitate? And why some liquids are obpaque while some are transparent?
Look for so called Tyndall effect.

Quote:

Here is a beaker. Inside is some oil on top of water. If the water is heated, so it becomes less thick and thus less dense, will it has a density lower than oil and so flow on the oil?
The simplest answer is oil is heated too so it becomes even less dense at the same time.

Besides, what is an 'oil'? It can be anything, from edible to car lubricant and I have no idea what range of densities is possible for substances that can be called 'oils'.

Monique Mar17-05 06:02 PM

Quote:

Quote by lwymarie
If a solution is heated to dryness, a powder will be left. But under evaporation, a crystal will form. So what's the difference between crystallization and vaporization? How is the process of crystallization?

When a solution precipitates very rapidly, there is not enough time for molecules to find their place in the lattice. For a crystal to form there first needs to be a 'seed', whose formation is energetically unfavourable.

Borek Mar18-05 03:43 AM

Quote:

Quote by Monique
When a solution precipitates very rapidly, there is not enough time for molecules to find their place in the lattice. For a crystal to form there first needs to be a 'seed', whose formation is energetically unfavourable.

While this is generally true it is all a matter of kinetics - which process is faster. I have never heard about amorphous form of strongly ionic compounds, like - say - KCl. Then, there are many things I haven't heard of :wink:


All times are GMT -5. The time now is 01:02 AM.

Powered by vBulletin Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
© 2014 Physics Forums