Rusting is a type of chemical reaction called a combination reaction.
A combination reaction means that substances combine to form one product.
Rusting is the combination of iron and oxygen.
Iron + Oxygen yields Iron Oxide (iron III oxide)
Iron oxide (rust) has a reddish brown color as shown in the picture of the rusty metal sign.
Conditions necessary for iron to rust:
1. oxygen must be present and in contact with the metal
2. the metal has to donate electrons and the oxygen accept them
3. there has to be a way, such as the presence of water, for the electron exchange to take place between the metal and oxygen
Conductors are materials that encourage the transfer of electrons.
Non-conductors are materials that interfere with the transfer of electrons.
Aqueous solution is a mixture of water and anything that will dissolve in it. Aqueous solution are conductors. This is why iron materials left out in the rain are more likely to rust than those that are kept dry.
Why doesn’t the painted part of the sign rust?
When covered by paint, the metal does not come in contact with oxygen. Scratches in the paint that expose the metal result in the exposed metal rusting.
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