F4 chem : rust

1. Tap water in some countries may contain high concentration of minerals (e.g. Ca^2+ and Mg^2+). Presence of these ions increase the electrical conductivity that increases the rate of rusting.

Distilled water contains dissolved oxygen while boiled distilled water does not contain any water. This is because the solubility of oxygen decreases when temperature increases. So rusting still occurs in presence of distilled water but not in boiled distilled water with a oily layer of the surface of solution.

2. Galvanization is not as same as sacrificial protection. Galvanization coats a layer of zinc on the surface of iron. It prevents the contact of oxygen and moisture in air with iron. So rusting will not occur.
However, sacrificial protection just sticks a more reactive metal (e.g. Mg, Al, Zn etc) to the iron. This ensures that the more reactive metal loses electrons more readily than the iron, which is so-called "sacrificed". The iron is prevented to lose electrons, thus rusting will not occur.

Zinc is poisonous, so it will not coat on food can. Besides, it coats on some iron jar that is for industrial purpose. So zinc can perform its function in this way.

3. Please post the questions you want to ask in Yahoo! Knowledge separately. A number of volunteers are willing to answer to your questions.

2011-12-01 21:37:58 補充：
Amendment:
Line 4: Distilled water contains dissolved oxygen while boiled distilled water does not contain any dissolved oxygen.

2011-12-01 21:39:25 補充：
Tap water that contains high concentration of minerals is usually called "hard water".

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