1. Oxidation-Reduction Reactions Chapter 4 Section 9 & 10 e-

2. Oxidation Reduction Reactions Reactions in which one or more electrons are transferred. That means elements change their charge from reactants to products. Most reactions that produce energy are redox Oxidation States Provide a way to keep track of electrons in oxidation reduction reaction. Imaginary charges in covalent compounds e-

3. Assigning Oxidation States  Element is 0  Monatomic ion is the charge of ion  Fluorine is -1; Oxygen is -2; Hydrogen is +1 Except peroxide, O 2 2-, where Oxygen is -1  Sum of oxidation states in a molecule must equal zero (electrons can be fractional) Charges are n+ or n– Oxidation States are +n or -n e-

4. C Assigning Oxidation States Examples O 2 = 0 + What is the oxidation state of carbon? (1 x C)(2 x -2)= 0 -4++4 = 0 C = +4

5. N e- Assigning Oxidation States Examples O 3 = 1- + What is the oxidation state of nitrogen? (1 x N)(3 x -2)= 1- -6++5 = 1- N = +5 1-

6. Fe e- Assigning Oxidation States Examples O 3 = 0 + What is the oxidation state of iron? (3 x Fe)(4 x -2)= 0 -8++8 = 0 Fe = +8/3 4 Can oxidation states be fractional? Yep.

7. Practice Problems Try page 174 #67 KMnO 4 NiO 2 Na 4 Fe(OH) 6 (NH 4 ) 2 HPO 4 e-

8. Practice Problems Try page 174 #67 P 4 O 6 XeOF 4 SF 4 CO e-

9. Practice Problems Try page 174 #67 C 6 H 12 O 6 e-

10. Balancing Redox Reactions - Acidic 1. Write the oxidation half reaction reaction separate from the reduction half reaction. 2. For each half reaction 1. Balance all elements except H & O 2. Balance O using H 2 O 3. Balance H using H + 4. Balance charges with e - 3. If necessary multiply each reaction by an integer to make the number of e - equal. 4. Combine half reactions, cancel identical species. 5. Double check elements and charges. e-

11. Practice Problems Sample Exercise 4.19 on page 165 H + + Cr 2 O 7 2- + C 2 H 5 OH  Cr 3+ + CO 2 + H 2 O e-

12. Balancing Redox Reactions - Basic 1. Work as if H + were present – like an acidic example 2. On each side add OH - to equal H + 3. Form H 2 O from OH - and H + e-

13. Practice Problems Sample Exercise 4.20 on page 167 Ag + CN - + O 2  Ag(CN) 2 - e-

14. Practice Problems Try page 174-175 #73c, 75b As 2 O 3 + NO 3 1-  H 3 AsO 4 + NO Mn 2+ + NaBiO 3  Bi 3+ + MnO 4 1- e-