Re: why do things rust and how can you make rust?

Dear Julia:

Rust is the chemical combination of iron with oxygen. It's an example of a very common and very important type of chemical change: OXIDATION, the combining of a material with oxygen. [There is a second meaning of oxidation which is broader and includes reactions that don't involve oxygen.]

Rust happens quite naturally, when iron contacts air. The air is about 1/5 oxygen gas. When a car is "rust-proofed" it is coated with a substance so that the oxygen in the air can't reach the iron. Take a look at an older car that has scratches on it. See how the red rust forms in the scratches, where the air can get at the metal?

You can speed up the rusting process by heating the iron, or adding water or saltwater. If you'd like to make rust, just leave an iron nail or piece of sheet iron in a jar of water or saltwater. Pretty soon the surface will be coated with a red flakey compound: iron oxide, or rust. This falls off and exposes the next layer of iron to the air, and the iron will continue to rust.

Almost all metals oxidize, and form OXIDES (compounds with oxygen). But not all metals form weak flakey compounds when they oxidize. For example, aluminum forms a very strong compound called aluminum oxide. This aluminum oxide forms a tough "skin" on the surface of the aluminum, preventing air from reaching the inner layers of metal. So the aluminum is protected from the air by its "rust" or oxide.

I enjoyed your question. Keep thinking and writing questions!