Question

Why aluminium tools are not affected by air and water?

Answer 1

I think it is because the phenomenon of Passivation.

Explanation:

Aluminium exposed to the atmosphere get covered by oxide that sticks to the surface and works as a protection coating stopping further damage to the material.

Answer 2

See Below.

Explanation:

Well, Actually, Aluminium is affected by air, but it sets up a preventive measure itself. (Oh How Smart..)

When Aluminium tools are new, the surfaces of the tools are brand new and have Fresh `Al` metal. This `Al` reacts with `O_2` present in air to from `Al_2O_3`, which forms a dull-whitish layer on the surfaces of the tools.

`2Al(s) + 3O_2(g) = Al_2O_3(s) darr` (deposition)

Now, This layer is quite friendly, and sticks with the surface of the tools, unlike iron rust, which flakes off. This oxide layer, prevents the exposure of the inner `Al` with air and water, so making it inert.

But, Washing the tools with solutions of caustic soda or detergents, makes everything crash down. The base acts on the oxide layer to form corresponding aluminate salt and water.

Here's the equation for what happens.

`Al_2O_3(s) + 2NaOH(aq) = 2NaAlO_2(aq) + H_2O(l)`

That reaction knocks off the oxide layer, and also the shield of the Aluminium tool. Poor Tool. R.I.P.

Hope this helps.