1. Lesson 35 What are oxidation and reduction?

2. Oxidation and reduction are opposite kinds of chemical reactions. Oxidation takes place when oxygen combines with another substance.

3. For example, when a flashbulb goes off, oxygen combines with aluminum.

4. The aluminum becomes oxidized. Aluminum oxide (Al 2 O 3 ) forms. 4Al + 3O 2 2Al 2 O 3 Aluminum + oxygen Aluminum oxide

6. Reduction takes place when oxygen separates from a compound. For example, electrolysis decomposes molten aluminum oxide. (Al 2 O 3 )

7. The oxygen separates from the aluminum. We say the aluminum oxide is reduced. 2Al 2 O 3 4Al + 3O 3 Aluminum Oxide aluminum oxygen

8. Here is another reduction equation. Notice what happens to the oxygen. 2Fe 2 O 3 + 3C 3CO 2 + 3Fe Iron Oxide Carbon carbon dioxide iron The oxygen has separated from the iron.

9. 2Fe 2 O 3 + 3C 3CO 2 + 3Fe However, the oxygen is not free oxygen. It is now part of the compound carbon dioxide.

10. It makes no difference whether a separated oxygen becomes free oxygen or part of a new compound.

11. As long as oxygen is separated from a compound, it is reduction.