Brine electrolysis with alluminum

[Mniazi]

I did an electrolysis with alluminum eletrodes, the electrolyte was NaCl, After completing it the left over was a gresyish precipitate (I assume aluminum hydroxide), I put most of it for evaporating in a cup, the rest evaporated leaving a jell, then later crystals. are the crystals NaCl which is covering the left over hydroxide or is it Sodium Alluminate.

 

[Greg Bernhardt]

I'm sorry you are not finding help at the moment. Is there any additional information you can share with us?

 

[cpman]

Firstly, sodium can not form a compound with aluminium. They are both metals, and except for rare cases, metals do not form compounds with each other.
Secondly, the percipitate is probably Al(OH)₃ like you suspected. Generally, Al(OH)₃ is a fine whitish percipitate. However, if your electrodes were aluminium foil, then the carbon coating could make the percipitate look grey,

Next, depending on how long the electrolysis ran, your crystals could be NaCl or NaClO, assuming you used an undivided cell. I highly doubt you ran it long enough for there to be any appreciable amount of NaClO in the solution, and you probably would have said that it smells like bleach. So, I am assuming the crystals are NaCl.

Generally, using NaCl as an electrolyte is not a good idea due to the evolution of chlorine gas, which is VERY dangerous. If you let it go long enough in an undivided cell with NaCl electrolyte, formation of NaClO (and Cl₂ gas dissolving in the solution) will turn it yellow.
So, if your solution did not turn yellowish, your crystals are probably NaCl.

 

[Borek]

Firstly, sodium can not form a compound with aluminium. They are both metals, and except for rare cases, metals do not form compounds with each other.

Aluminates are quite common, http://en.wikipedia.org/wiki/Sodium_aluminate

In general, binary compounds (like caesium auride) are rare, but many metals are amphoteric and capable of producing salts - Al, Zn, Cr, Mn being the best known examples.