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Understanding Oxidation and Reduction Reactions in Chemistry

Learn about electron transfer, oxidation numbers, and identifying oxidizing and reducing agents in oxidation-reduction reactions.

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Understanding Oxidation and Reduction Reactions in Chemistry

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  1. Chapter 14 Oxidation-Reduction: Transfer of Electrons

  2. Oxidation and Reduction An oxidation-reduction reaction: • Provides us with energy from food • Provides electrical energy in batteries • Occurs when iron rusts 4Fe + 3O2 2Fe2O3

  3. Electron Loss and Gain An oxidation-reduction reaction: • Transfers electrons from one reactant to another • Loses electrons in oxidation (LEO) Zn Zn2+ + 2e- (loss of electrons) • Gains electrons in reduction (GER) Cu2+ + 2e- Cu (gain of electrons)

  4. Oxidation and Reduction

  5. Zn and Cu2+ Zn Zn2+ + 2e- Silvery metal Cu2+ + 2e- Cu Blue orange solid

  6. Electron Transfer from Zn to Cu2+ Oxidation: electron loss Reduction: electron gain

  7. Learning Check Identify each of the following as: 1) oxidation or 2) reduction __A. Sn Sn4+ + 4e− __B. Fe3+ + 1e−Fe2+ __C. Cl2 + 2e− 2Cl-

  8. Learning Check In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction. UV light Ag+ + Cl− Ag + Cl A. Which reactant is oxidized? B. Which reactant is reduced?

  9. Oxidizing and Reducing Agents In the reaction, Mg(s) + Cl2(g) MgCl2(s) Mg Mg2+ + 2e− oxidation Mg is the reducing agent, because it provides electrons when oxidized. Cl2 +2e− 2Cl reduction Cl2 is the oxidizing agent, because it accepts electrons when reduced.

  10. Summary of Oxidation and Reduction Terms

  11. Oxidation Numbers An oxidation number: • Is assigned to each atom in a compound or ion • For the more electronegative atom is negative • Identifies oxidation or reduction • Keeps track of the loss and gain of electrons

  12. Assigning Oxidation Numbers 1. Element in the pure state is zero. Al 0 Cl2 0 Cu 0 2. A monoatomic ion equals its charge Na+ 1+ S2- 2- Fe3+ 3+ 3. The sum of the oxidation numbers of all the atoms in a neutral formula = 0

  13. Assigning Oxidation Numbers 4. The sum of all the oxidation number of all the atoms in a polyatomic ion = charge of ion 5. Oxidation numbers are assigned in order of priority, as follows: Group 1A(1) Li, Na,K +1 Group 2 A(2) Mg, Ca +2 Hydrogen H +1 Fluorine F -1 Oxygen O -2 Group 7A (17) (usually Cl, Br, I) -1

  14. Examples of Oxidation Numbers Assign oxidation numbers to the atoms in each of the following: MgCl2 MgCl2 +2 -1 2A(2) = +2; 7A (17) = -1 CCl4 CCl4 +4 -1 C + 4(-1) = 0 C = +4 PO43−PO43− +5 -2 P + -4(-2) = -3 P = -3 + 8 = +5

  15. Learning Check Identify the substances that are oxidized and reduced in the following reactions: A. 4Fe(s) + 3O2(g) 2Fe2O3(s) B. 6Na(s) + N2(g) 2Na3N(s) C. 2K(s) + I2 (g) 2KI (s)

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