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Ch. 5 Oxidation and Reduction

Ch. 5 Oxidation and Reduction. Milbank High School. Ch. 5 Objectives. Define some important properties of oxygen List important properties of hydrogen Describe oxidation and reduction Identify an oxidation/reduction reaction Identify some common oxidizing and reducing agents

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Ch. 5 Oxidation and Reduction

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  1. Ch. 5Oxidation and Reduction Milbank High School

  2. Ch. 5 Objectives • Define some important properties of oxygen • List important properties of hydrogen • Describe oxidation and reduction • Identify an oxidation/reduction reaction • Identify some common oxidizing and reducing agents • List some of the important oxidization and reduction reactions involving living organisms

  3. Overview • Oxidation and reduction reactions always occur together (redox reactions) • You can’t have one without the other • Includes: extracting metal from an ore • Salt on roads • Salt accelerates the reaction between oxygen and metal • Makes electron transfer easier

  4. Oxygen • Most abundant element on Earth • 21% of our atmosphere (pure) • 89% of Earth’s water (compound) • 45.5% of Earth’s crust (compound) • 2/3rd’s of the human body (compound) • Foods (compound) • Rust

  5. Chemical Properties of Oxygen • Combines with many elements and compounds • Rust (reacts with metals) • Other oxides (reacts with nonmetals) • Methane (reacts with other compounds) • Bunsen burner

  6. Hydrogen • In the universe, 95% of all atoms are hydrogen • Seldom found alone • Hydrocarbons • Hindenburg…

  7. 3 ways of looking at oxidation and reduction • 1. oxidation is a gain of oxygen atoms, reduction is a loss of oxygen atoms • 2. oxidation is a loss of hydrogen atoms, reduction is a gain of hydrogen atoms • 3. oxidation is a loss of electrons, reduction is a gain of electrons • Most fundamental explanation, what we will be dealing with the most

  8. Oxygen Hydrogen e-

  9. In relation to our lab… • Remember that reduction is a loss of oxygen from a compound • We converted iron ore to metallic iron • We removed oxygen from the iron(III) oxide • 2Fe2O3 + 3C  4Fe + 3CO2 • Carbon was oxidized because it gained an oxygen

  10. Leo the Lion! • LEO the lion says GER • Loss of electrons is oxidation, gain of electrons is reduction

  11. Examples • Is the reactant oxidized or reduced? • Pb  PbO3 • SnO2  SnO • KClO3 KCl • C2H6O  C2H4O • C2H2  C2H6

  12. Pertaining to LEO… • Mg + S  MgS • Mg + S  Mg2+ + S2- • Magnesium is oxidized • Said to be the reducing agent • Substance in the reaction that loses electrons • Sulfide sulfur atom is reduced • Said to be the oxidizing agent • Substance in the reaction that gains electrons

  13. Oxidation Numbers • A count of the electrons transferred or shared in the formation or breaking of chemical bonds • You must assign each element in the reaction an oxidation number • Follow a set of rules…

  14. Oxidation Number Rules 1. The total of the oxidation numbers of all the atoms in a neutral molecule, an isolated atom, or a formula unit is 0 • Examples 2. In their compounds, the Group 1A metals all have an oxidation number of +1, and the Group 2A metals have an oxidation number of 2+. • Examples

  15. Rules Con’t 3. In its compounds, hydrogen has an oxidation number of +1 (except in metal hydrides such as NaH, where it is -1) • Examples 4. In its compounds, oxygen has an oxidation number of -2 (except in peroxides such as H2O2, where it is -1) • Examples 5. In their binary compounds with metals, Group7A elements have an oxidation number of -1. Group 6A elements have an oxidation number of -2, and Groups 5A elements have an oxidation number of -3. • Examples

  16. Problems • What is the oxidation number of each element? • I2 • Cr2O3 • AlCl3 • Na2SO4 • CaH2

  17. Identifying Redox Reactions 0 +3 -2 0 +3 -2 • 2 Al + Fe2O3 2 Fe + Al2O3 • Al increases from 0 to +3, it is ______ • Oxidized! • Fe decreases from +3 to 0, it is _______ • Reduced!

  18. Problems • Zn  Zn2+ • Fe3+  Fe2+ • CaCO3  CaO + CO2 • AgNO3  Ag • Do Practice Exercises

  19. Oxidizing and Reducing Agents • Now the confusing part… • CuO + H2 Cu + H2O • Cu goes from +2 to 0 • Cu is reduced, therefore it is called an oxidizing agent because it causes some other substance to be oxidized • H goes from 0 to +1 • H is oxidized, therefore it is called a reducing agent because it causes some other substance to be reduced.

  20. Identifying Agents in an Equation • CuO + H2 Cu + H2O Reduction: CuO is the oxidizing agent Oxidation: H2 is the reducing agent

  21. Some common oxidizing agents • Oxygen! • Oxidized coal in electric power • Gas in automobiles • Wood in campfires • Food we eat • Antiseptics • Hydrogen Peroxide • Benzoyl peroxide • Disinfectants • Chlorine

  22. Some common reducing agents • Metals • Antioxidants • Ascorbic acid is used to prevent the browning of fruits by inhibiting air oxidation • Many antioxidants are believed to retard various oxidation reactions that are potentially damaging to vital components of living cells

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