1. Redox Reactions Chapter 18 + O 2 

2. Oxidation-Reduction (Redox) Reactions “redox” reactions: rxns in which electrons are transferred from one species to another oxidation & reduction always occur simultaneously we use OXIDATION NUMBERS to keep track of electron transfers

3. Rules for Assigning Oxidation Numbers: 1) the ox. state of any free (uncombined) element is zero. Ex: Na, S, O 2, H 2, Cl 2, O 3

4. Rules for Assigning Oxidation Numbers: 2) The ox. state of an element in a simple ion is the charge of the ion. Mg 2+  oxidation of Mg is +2

5. Rules for Assigning Oxidation Numbers: 3) the ox. # for hydrogen is +1 (unless combined with a metal, then it has an ox. # of –1) Ex: NaOH (H bonded to O) v. NaH (H bonded to Na) H = +1H = -1

6. Rules for Assigning Oxidation Numbers: 4) the ox. # of fluorine is always –1.

7. Rules for Assigning Oxidation Numbers: 5) the ox. # of oxygen is usually –2. Why USUALLY? Not -2 when it’s in a peroxide, such as hydrogen peroxide: H2O2H2O2

8. Rules for Assigning Oxidation Numbers: 6) in any neutral compound, the sum of the oxidation #’s = zero.

9. Rules for Assigning Oxidation Numbers: 7) in a polyatomic ion, the sum of the oxidation #’s = the overall charge of the ion.

10. Rules for Assigning Oxidation Numbers: **use these rules to assign oxidation #’s; assign known #’s first, then fill in the #’s for the remaining elements:

11. Examples: Assign oxidation #’s to each element: a) NaNO 3 Na = +1 O = -2 Therefore, N = +5

12. Examples: Assign oxidation #’s to each element: b) SO 3 2- O = -2, therefore S must = +4 to balance the charges and have an overall charge of 2- -2+4

13. Examples: Assign oxidation #’s to each element: c) HCO 3 - -2+1+4

14. Examples: Assign oxidation #’s to each element: Do on your own: d) H 3 PO 4 e) Cr 2 O 7 2- f) K 2 Sn(OH) 6

15. Definitions Oxidation: the process of losing electrons (ox # increases) Reduction: the process of gaining electrons (ox # decreases) Oxidizing agents: species that cause oxidation (they are reduced) Reducing agents: species that cause reduction (they are oxidized)

16. To help you remember… OIL RIG Oxidation Is Loss Reduction Is Gain

17. OR… LEO GER Losing Electrons → Oxidation Gaining Electrons → Reduction

18. Are all rxns REDOX rxns? You must determine this… a reaction is “redox” if a change in oxidation # happens; if no change in oxidation # occurs, the reaction is nonredox.

19. Examples MgCO 3  MgO +CO 2 +2-2 MgCO 3 is an ionic compound, so what is Mg’s charge in an ionic compound? The carbonate ion CO 3 2- is the other ion, let’s figure out C because we already know O. +4 -2+2-2+4 Is this a redox or nonredox reaction? NONREDOX (no change in oxidation numbers)

20. Examples Zn + CuSO 4  ZnSO 4 + Cu Which oxidation numbers do we already know? 0, free element 0 Break down this ionic compound into its ions Cu and SO 4 2- So, Cu must be Cu 2+ +2 O = -2 in SO 4 2-, so S must be…? -2 +6 -2 +2+6 Is this a redox or nonredox reaction? REDOX reaction

21. Examples NaCl + AgNO 3  AgCl + NaNO 3 Redox or nonredox?

22. Examples CO 2 + H 2 O  C 6 H 12 O 6 + O 2 -2+4 -2+1 0-2 +1 0 What happened to Carbon? It went from +4 oxidation # to 0. Was Carbon oxidized or reduced? REDUCED OIL RIG (oxidation is losing electrons so oxidation number increases, where as reduction is gaining electrons so oxidation number decreases)