Sodium Hydroxide + Aluminium -->

Sodium Hydroxide + Aluminium --> What do you make of this?

#1 darkfang77

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Posted 19 August 2010 - 09:30 PM

OK, this question isn't related to pyrotechnics, but it is related to chemistry.
Having seen the reaction between NaOH and Aluminium a few times, I still can't work out what happens in the equation.
As far as I know, sodium is far more reactive than aluminium to displace it to aluminium hydroxide so the formula,
(NaOH + Al --> AlOH + Na) is wrong, it isn't balanced, I know.

Does anyone have any theories as to what the end products are?

Moreover, in the equation:

sodium hydroxide + aluminium... the aluminium is group 3, and the sodium is group 1.
From what I learnt in chemistry, anything group 4 or less usually lose the electrons in their outer shell in order to form ions with negatively charged elements. In this equation, both reactants are below group 4, therefore, how do they form compounds (ionic or covalent) if there are no negatively charged particles to form the electrostatic bonds??

Granted, the sodium hydroxide will be in solution, but how does this come into the equation???

If I have made some massive blunder that school chemistry doesn't cover, my apologies.

#2 Mumbles

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Posted 20 August 2010 - 09:19 AM

As a big generalization, it forms sodium aluminate.

NaOH + Al + 3 H2O ---> Na[Al(OH)4] + 1.5 H2

#3 Guest_anyka_*

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Posted 24 August 2010 - 02:08 PM

Mumbles, on 20 August 2010 - 09:19 AM, said:

As a big generalization, it forms sodium aluminate.

NaOH + Al + 3 H2O ---> Na[Al(OH)4] + 1.5 H2

Yes, a big generalization.
Sodium aluminate is usually formed by the action of sodium hydroxide on elemental aluminium. The reaction is very very exothermic once established and is accompanied by the rapid evolution of hydrogen gas. The reaction iswritten as:

2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂

#4 Mumbles

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Posted 24 August 2010 - 05:40 PM

What you wrote and I wrote are the exact same thing. [Al(OH)₄]^- and AlO₂^- are both accepted ways to describe the aluminate ion. One better represents the species in solution, and one represents the empirical formula of the solid. A somewhat more correct representation would be Na₂Al₂O₄ as the aluminum is tetrahedral, and the whole thing exists in a polymeric network.

#5 Guest_anyka_*

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Posted 24 August 2010 - 06:11 PM

Mumbles, on 24 August 2010 - 05:40 PM, said:

True true, the most usual way it is made is the way I presented it I just wished to show an alternate method..
But, lol..all roads lead to Rome. The ends justify the means.

#6 MDH

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Posted 24 August 2010 - 08:45 PM

I'm interested in how the aluminates are useful in pyrotechnics to some degree. Has anybody tried experimenting with them? Are the other aluminates insoluble?

#7 Mumbles

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Posted 25 August 2010 - 05:07 AM

What uses do you have in mind? You'll be very disappointed if you think they'll give up any oxygen. I don't know much about aluminates as far as properties. If they are soluble, they are quite basic and corrosive, just so you know. I don't think they'll play nice with too many metals.