1. LEO SAYS GER Textbook ch 4.4 Oxidation-Reduction Reactions “Redox” Unit 1: Chemistry Basics 1.42 Oxidation-Reduction Reactions “Redox”

2. Oxidation and Reduction (Redox)  Electrons are transferred  Spontaneous redox rxns can transfer energy  Electrons (electricity)  Heat  Non-spontaneous redox rxns can be made to happen with electricity

3. Oxidation Reduction Reactions (Redox) Each sodium atom loses one electron: Each chlorine atom gains one electron:

4. LEO says GER : Lose Electrons = Oxidation Sodium is oxidized Gain Electrons = Reduction Chlorine is reduced One cannot occur without the other

5. Rules for Assigning Oxidation Numbers Rules 1 & 2 1.The oxidation number elements in their elemental form is zero. 2. The oxidation number of a monatomic ion equals its charge

6. Rules for Assigning Oxidation Numbers Rules 3 & 4 3. The oxidation number of oxygen in compounds is -2 4. The oxidation number of hydrogen in compounds is +1

7. Rules for Assigning Oxidation Number Rule 5 5. The sum of the oxidation numbers in the formula of a compound is 0 2(+1) + (-2) = 0 H O (+2) + 2(-2) + 2(+1) = 0 Ca O H

8. Rules for Assigning Oxidation Numbers Rule 6 6. The sum of the oxidation numbers in the formula of a polyatomic ion is equal to its charge

9. Not All Reactions are Redox Reactions Reactions in which there has been no change in oxidation number are not redox rxns. Examples:

10. Trends in Oxidation and Reduction Active metals: Lose electrons easily Are easily oxidized Active nonmetals: Gain electrons easily Are easily reduced

11. Calculate the oxidation #s

12. Weirdo exceptions : Weirdo exceptions : Rules 3 & 4 3. The oxidation number of oxygen in compounds is -2 ( Note: Except in the peroxide ion in which it has an oxidation number of −1.) 4. The oxidation number of hydrogen in compounds is +1 (Note: Except when bonded to a metal, in which it has an oxidation number of -1)

13. Oxidation of a metal in Single Replacement reactions Hydrochloric acid reacts with Zinc metal. Write oxidation #s 2HCl (aq) + Zn (s)  ZnCl 2 + H 2(g) Note: As written Zinc replaces the hydrogen ion in the reaction

14. WAIT! - How do you know the reaction WILL occur??? Will hydrochloric acid oxidize zinc metal? HCl (aq) + Zn (s)  ?????? Sometimes chemicals don’t react.

15. For single replacement reactions we consult activity series to predict if reaction will occur. We want to “see” if single element can oxidized and “replace” a like ion in the compound. Look at single element…is it higher in the chart than a like ion (metal replace metals) I will give you a copy of the activity series to use on test Activity series

16. metals –greater activity = easier to lose electrons –i.e. easier to become a cation nonmetals –greater activity = easier to gain electrons –i.e. easier to become an anion

17. Will an aqueous solution hydrochloric acid oxidize zinc metal? If so, write the net ionic equation Because Zn is higher on activity series than H- the reaction will occur. Zn will replace H in the compound. HCl (aq) + Zn (s) 

18. calcium and lead (II) nitrate copper and lithium sulfate