Chapter 14 Oxidation- Reduction: Transfer of Electrons

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

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

Oxidation and Reduction

Zn and Cu 2+ Zn Zn e- Silvery metal Cu e- Cu Blueorange solid

Electron Transfer from Zn to Cu 2+ Oxidation: electron loss Reduction: electron gain

Identify each of the following as: 1) oxidation or 2) reduction __A. SnSn e − __B. Fe e − Fe 2+ __C. Cl 2 + 2e − 2Cl - 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? Learning Check

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

Summary of Oxidation and Reduction Terms

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 Oxidation Numbers

1. Element in the pure state is zero. Al0 Cl 2 0 Cu0 2. A monoatomic ion equals its charge Na + 1+ S Fe The sum of the oxidation numbers of all the atoms in a neutral formula = 0 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 HydrogenH+1 Fluorine F-1 Oxygen O-2 Group 7A (17) (usually Cl, Br, I)-1 Assigning Oxidation Numbers

Examples of Oxidation Numbers Assign oxidation numbers to the atoms in each of the following: MgCl A(2) = +2; 7A (17) = -1 CCl C + 4(-1) = 0 C = +4 PO 4 3− +5 -2P + -4(-2) = -3 P = = +5

Learning Check Identify the substances that are oxidized and reduced in the following reactions: A. 4Fe(s) + 3O 2 (g) 2Fe 2 O 3 (s) B. 6Na(s) + N 2 (g) 2Na 3 N(s) C. 2K(s) + I 2 (g) 2KI (s)