[HSOoi]

Hi there,

Aluminum is higher than Hydrogen in electrochemical series.
This means Aluminum is more probably to become an ion compared with Hydrogen.

So,
Aluminum react with Hot Water to form Aluminum Oxide and Hydrogen Gas, right?

3H₂O + 2Al  Al₂O₃ + 3H₂

Since then why do we use Aluminum foil to store food? 

[408]

Think about what forms on the surface of aluminum...that may prevent reaction with water...

[HSOoi]

Think about what forms on the surface of aluminum...that may prevent reaction with water...

Well, seems like the only thing to prevent the reaction is that thin oxide layer?
Doesn't sound safe to me. LOL 

[408]

An acidic dish will actually burn through aluminum foil.  I threw out some chilli once that I covered in aluminum foil, and the next day I found a hole in the top!

[Arkcon]

There was actually a term for this phenomena, but Wikipedia has gone and merged it with another term.  At any rate, the lasagna battery -- http://en.wikipedia.org/wiki/Lasagna_battery#Lasagna_cell

[magician4]

the effect is called "passivation" , and asides from Al protects a lot of other valuable materials from vehement and fast rotting (like for example: steel)


regards

Ingo

[curiouscat]

A lot of practical corrosion behavior seems based on the tenacity of the oxide layer than the reactivity of the underlying metal. e.g. Titanium / Tantalum are very resistant to corrosion I believe on similar grounds.

OTOH, I wonder if Chemistry heuristics would let us predict this tenacity. Could one predict which oxides will protect & which ones won't?

[408]

The oxide layer on niobium is amazing as well.  A fresh piece hooked up as anode in an electrolytic cell in, say, HCl, will give electrolysis of the solution for a few seconds, but very soon after the current density will drop off from the insulating oxide layer formed.

The potential applied will determine the color of the oxide layer, a very nice blue comes at either 5V or 12V, forget which.