# Testing a sodium aluminate solution

I prepared some sodium aluminate by reacting a strong $NaOH$ solution with aluminium foil and filtering the result. I now have a clear solution and I'm not sure what it is. I stopped adding aluminium when the reaction rate showed down dramatically in a hot water bath. Basically what I'm asking is what are the properties of sodium aluminate since Wikipedia is severely lacking in information on sodium aluminate

There are multiple reactions going on simultaneously. Aluminum metal reacts with the oxygen in surrounding air in order to create a plating of aluminum (III) oxide.

$$\ce{4Al(s) + 3O2(l) -> 2Al2O3(s)}$$

Upon addition of sodium hydroxide, the oxide layer reacts with the base, leaving the aluminum free to attack by water for instance.

$$\ce{2 Al + 6 H2O -> 2 Al(OH)3 + 3 H2}$$ $$\ce{Al(OH)3 + NaOH -> Na+ + [Al(OH)4]-}$$

In summary, we can write the sum of the reactions as:

$$\ce{2Al(s) + 2NaOH(aq) + 6H2O(l) -> 2Na+(aq) + 2[Al(OH)4]- + 3H2(g)}$$

The reason why the reaction proceeded slowly at first was due to the aluminum (III) oxide layer covering the aluminum metal.