Why can't you remove hydroxide from Al(OH)3 with alkali metals?

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Discussion Overview

The discussion revolves around the feasibility of removing hydroxide ions from aluminum hydroxide (Al(OH)3) using alkali metals such as sodium or potassium. Participants explore the chemical reactions involved, particularly in both aqueous and non-aqueous environments, and the thermodynamic implications of these reactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that reacting sodium or potassium with Al(OH)3 should work based on electronegativity considerations but is unsure of the reasoning behind its failure.
  • Another participant requests a reaction equation to clarify the proposed reaction.
  • A proposed reaction equation is given: 3Na + Al(OH)3 → Al + 3NaOH, but its feasibility is questioned.
  • It is noted that thermodynamic stability of products is crucial, with the formation of sodium aluminate and hydrogen gas being highlighted as likely outcomes in the presence of water.
  • A participant suggests that in a non-aqueous reaction, a possible equation could be 4Na + 2Al(OH)3 → 2NaAlO2 + 2NaOH + H2, although this is not definitive.
  • Another participant raises the possibility of mixed oxides like Na2O·Al2O3 being formed as a likely product in the reaction.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the reactions and products formed, indicating that there is no consensus on the feasibility or outcomes of the proposed reactions.

Contextual Notes

The discussion includes assumptions about the stability of reaction products and the conditions under which the reactions occur, such as the presence or absence of water, which remain unresolved.

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So I've tried to research a bit on refining aluminum without fluorine, and I came up with the idea of reacting the hydroxide off aluminum hydroxide with sodium or potassium. Only problem is, the reaction doesn't work, according to what I've found. I'm curious why, as the electronegativity table seems to indicate that Na or P should preferentially react with the hydroxide ions.

I appear to have a gap in my reasoning somewhere, so what am I missing?
 
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No idea what kind of reaction you are talking about, please write the reaction equation.
 
If it worked, it would be 3Na + Al(OH)3 → Al + 3NaOH.
 
OK

Electronegativities are not the only thing that matters. What matters is the thermodynamical stability of products. In this case mixture of Al and NaOH is not stable - Al nicely dissolves in the alkali producing sodium aluminate. In the presence of water reaction is (more or less)

2NaOH + 2Al + 2H2O → 2NaAlO2 + 3H2

When there is no water around situation gets more complicated, but you can still expect hydrogen to evolve and some kind of aluminate or mixed oxide to be produced. That's because Al is amphoteric, and its hydroxide can react both as an acid and as a base.
 
So for the non-aqueous reaction, it would be something like, but not necessarily, 4Na + 2Al(OH)3 → 2NaAlO2 + 2NaOH + H2?
 
I would check if there is no mixed oxide like Na2O·Al2O3 - which would be a most likely product then.

Many salts can be described as mixed oxides, and they are present in many minerals (see for example http://en.wikipedia.org/wiki/Spinel_group).
 
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