2. Redox Reactions

3. Redox Equations: At the conclusion of our time together, you should be able to: 1.Define redox 2.Figure out oxidation numbers for any element 3.Show the change in oxidation numbers in a reaction

4. What’s the Point ? Electrical production (batteries, fuel cells) REDOX reactions are important in … Purifying metals (e.g. Al, Na, Li) Producing gases (e.g. Cl 2, O 2, H 2 ) Electroplating metals Protecting metals from corrosion Balancing complex chemical equations Sensors and machines (e.g. pH meter) C 3 H 8 O + CrO 3 + H 2 SO 4  Cr 2 (SO 4 ) 3 + C 3 H 6 O + H 2 O

5. What is Redox? REDOX stands for REDuction/OXidation Oxidation refers to a loss of electrons Reduction refers to a gain of electrons As a mnemonic remember LEO says GER Lose Electrons = Oxidation Gain Electrons = Reduction

6. Review of Oxidation Numbers We will see that there is a simple way to keep track of oxidation and reduction This is done via “oxidation numbers” Similar to the idea of ionic charges, but have to apply different rules when dealing with covalent compounds

8. 1.Any element, when not combined with atoms of a different element, has an oxidation # of zero. (O in O 2 is zero, Na by itself is zero) 2.Any simple monatomic ion (one-atom ion) has an oxidation number equal to its charge (Na + is +1, O 2– is –2) 3.The sum of the oxidation numbers of all of the atoms in a formula must equal the charge written for the formula. (if the oxidation number of O is –2, then in CO 3 2– the oxidation number of C is +4) Review of Oxidation Numbers

9. 4. In compounds, the oxidation # of IA metals is +1, IIA is +2, IIIA is +3, Zn & Cd is +2, Ag is +1. 5. In ionic compounds, the oxidation # of a nonmetal or polyatomic ion is equal to the charge of its associated ion. (MgCl 2, Mg is +2, therefore Cl is –1) 6. F is always –1, O is always –2 (unless combined with F), H is usually +1, except when it is bonded to metals in binary compounds. (ex. NaH, H oxidation # is –1 or when it’s in elemental form H 2, oxidation # is 0).

10. NaIO 3 IF 7 Oxidation numbers of all the elements in the following ?

11. The Remainder of Redox Step 3: Determine which element is being reduced. Connect them and mark # of electrons gained. Step 4: Determine which element is being oxidized. Connect them and mark # of electrons lsot.

12. Determination of Oxidation and Reduction If oxidation # decreased; substance reduced (oxidizing agent) If oxidation # increased; substance oxidized (reducing agent)

13. Example 2K + F 2  2KF CH 4 +O 2  CO 2 + H 2 O

14. Example 1 Al + O 2  Al 2 O 3

15. Example 2 FeO  Fe + O 2

16. Example 3 Mg + PbCl 4  Pb + MgCl 2

17. Example 4 Ba(NO 3 ) 2 + Na 3 PO 4  Ba 3 (PO 4 ) 2 + NaNO 3