Al2O3 in molten Cryolite

[Romix]

What happening to aluminium oxide in molten cryolite (Na₃AlF₆) at 1000°C ?

[John Cuthber]

At that temperature aluminium oxide will dissolve in cryolite.

 

If you pass an electric current through the solution you will get aluminium metal and oxygen (which will probably attack the electrode).

[Romix]

At that temperature aluminium oxide will dissolve in cryolite.

 

If you pass an electric current through the solution you will get aluminium metal and oxygen (which will probably attack the electrode).

Yes agree, if electrodes were made of carbon, platinum electrodes will be fine.

 

What actually happens to the molecules when cryolite used as solvent to dissolve aluminium oxide?

For H2O and NaCl google gave me this picture.

 

Not shore if its right.

Here is anion and cation of NaCl in solution of H2O.

 

Still don't get it, why dissolution happening? Why some salts are insoluble.

Is it something to do with their electron configuration?

Alright lets start from simple insoluble ionic metal salts.

Barium Sulphate

Lead Chloride and Sulphate

Silver Chloride

 

That's the electron configuration of metals.

 

Silver

Barium

Lead

 

Anion:

SO4 with a -2 charge and Cl with a -1 charge.

Silver transfers one electron to chlorine atom. Usually it happening in displacement reaction, but can be done directly with addition of H2O2.

Ok no electrons left in its 5th outer shell, and chlorine filled its shells.

Strong ionic bond.

 

Same situation I see in bonding Sodium with Chlorine.

But salt produced is soluble.

Maybe because Sodium is Alkali Metal, and its electrons really close to the nucleus?

 

Barium Sulphate another insoluble salt.

Barium have 2 electrons in its outer shell.

[ba+2][sO4-2]

All its shells filled.

This time anion not just atom, its a molecule.

Lead Chloride & Sulphate are both insoluble.

4 electrons in its outer shell...

Why this salts are insoluble?

Edited December 9, 2014 by Romix