1. “Oxidation-Reduction Reactions” LEO SAYS GER

2. The Meaning of Oxidation and Reduction (called “redox”) OBJECTIVES: Define oxidation and reduction in terms of the loss or gain of oxygen, and the loss or gain of electrons. State the characteristics of a redox reaction and identify the oxidizing agent and reducing agent.

3. Oxidation and Reduction (Redox) Early chemists saw “oxidation” reactions only as the combination of a material with oxygen to produce an oxide.

4. Oxidation and Reduction (Redox) For example, when methane burns in air, it oxidizes and forms oxides of carbon and hydrogen. http://www.saburchill.com/chemistry/chapters/chap023.html

5. Oxidation and Reduction (Redox) But, not all oxidation processes that use oxygen involve burning:

6. Oxidation and Reduction (Redox) Elemental iron slowly oxidizes to compounds such as iron (III) oxide, commonly called “rust” http://fineartamerica.com/featured/old-car-and-rust-danny-jones.html http://www.texample.net/tikz/examples/rusting-iron/

7. Oxidation and Reduction (Redox) Bleaching stains in fabrics http://www.ehow.com/about_4605079_bleach-spots.html

8. Oxidation and Reduction (Redox) Hydrogen peroxide also releases oxygen when it decomposes http://site.destinationgreen.com/?p=2530

9. Oxidation and Reduction (Redox) A process called “reduction” is the opposite of oxidation, and originally meant the loss of oxygen from a compound Oxidation and reduction always occur simultaneously The substance gaining oxygen (or losing electrons) is oxidized, while the substance losing oxygen (or gaining electrons) is reduced.

10. Oxidation and Reduction (Redox) Today, many of these reactions may not even involve oxygen Redox currently says that electrons are transferred between reactants Mg + S → Mg 2+ + S 2- The magnesium atom (which has zero charge) changes to a magnesium ion by losing 2 electrons, and is oxidized to Mg 2+ The sulfur atom (which has no charge) is changed to a sulfide ion by gaining 2 electrons, and is reduced to S 2- (MgS)

11. LEO says GER Losing Electrons Oxidation Gaining Electrons Reduction

12. LEO says GER : LEO says GER : Each sodium atom loses one electron: Each chlorine atom gains one electron:

13. LEO says GER : LEO says GER : Lose Electrons = Oxidation Sodium is oxidized Gain Electrons = Reduction Chlorine is reduced

14. LEO says GER : LEO says GER : - Losing electrons is oxidation, and the substance that loses the electrons is called the reducing agent. - Gaining electrons is reduction, and the substance that gains the electrons is called the oxidizing agent. Mg (s) + S (s) → MgS (s) Mg is oxidized: loses e -, becomes a Mg 2+ ion S is reduced: gains e - = S 2- ion Mg is the reducing agent S is the oxidizing agent

15. Not All Reactions are Redox Reactions - Reactions in which there has been no change in oxidation number are NOT redox reactions. Examples:

16. Identifying Redox Equations In general, all chemical reactions can be assigned to one of two classes: 1)oxidation-reduction, in which electrons are transferred: Single-displacement, synthesis, decomposition, and combustion 2)this second class has no electron transfer, and includes all others: Double-displacement and acid- base reactions

17. Identifying Redox Equations In an electrical storm, nitrogen and oxygen react to form nitrogen monoxide: N 2(g) + O 2(g) → 2NO (g) Is this a redox reaction? If the oxidation number of an element in a reacting species changes, then that element has undergone either oxidation or reduction; therefore, the reaction as a whole must be a redox. YES!