1. OXIDATION-REDUCTION REACTIONS (REDOX) A Change in Charge Click here to start the podcast

2. REDOX BASICS transfer of electrons between two atoms NaF

3. Oxidation Numbers the ox. # of free elements is ZERO (including diatomics like O 2 and polyatomics like P 4 or S 8 ) the ox. # of a monatomic ion = its charge (like Na +1 ) Other elements: o O = -2 (except in peroxide, each O = -1) o H = +1 (except in metal hydrides, then H = -1) o Halogens = -1 (except when central atom of polyatomic ions, like ClO 3 -1 )

4. Identify the oxidation number for the underlined element H 2 O H 2 O 2 FeSO 4 HClO HClO 2 HClO 3 HClO 4 Click here for answers

5. Is it Oxidation or Reduction or neither? 1.Silver ions change to raw (elemental) silver 2.Hydrogen gas changes to hydrogen ions 3.Blue CrCl 2 changes to green CrCl 3 4.Yellow K 2 CrO 4 changes to orange K 2 Cr 2 O 7 Click here for answers

6. Oxidation-Reduction Reactions Single Replacement: Zn(s) + HCl(aq)  ZnCl 2 (aq) + H 2 (g) Synthesis: Mg(s) + O 2 (g)  MgO(s) Decomposition: Fe 2 O 3 (s)  Fe(s) + O 2 (g) Combustion: CH 4 (g) + O 2 (g)  CO 2 (g) + H 2 O(g) These types of reactions can be balanced by inspection

7. Redox reactions in acid/base solutions MnO 4 - + S 2 O 3 -2 + H +  Mn +2 + SO 4 -2 + H 2 O Br 2 + OH -  Br - + BrO 3 - + H 2 O S 8 + O 2 + H 2 O  SO 4 -2 + H + These will be balanced using the method of half-reactions

8. Balancing with Half-Reactions 1.Split the reaction into half reactions involving similar species (ignore H +, OH -, and H 2 O) 2.Balance atoms of all elements EXCEPT O and H 3.Balance O by adding H 2 O to the side that has fewer O atoms 4.Balance H by adding H + to the side that has fewer H atoms a.If acidic solution: continue on to step 5 b.If basic solution: add enough OH- to the same side that you added H+ to. Change H+ and OH- to H2O. Add same amount of OH- to the other side. 5.Balance by CHARGE a.Determine total charge on each side of each half-reaction b.Add electrons to the more positive side c.Use a multiplier to get electrons in each reaction to be equal 6.Add half reactions together and cancel any terms that are the same on opposite sides.

9. MnO 4 - + S 2 O 3 -2 + H +  Mn +2 + SO 4 -2 + H 2 O

10. Br 2 + OH -  Br - + BrO 3 - + H 2 O

11. Fe +2 + Cr 2 O 7 -2  Fe +3 + Cr +3 (in acidic solution) Click here for answers

12. S 8  S 2 O 3 -2 + S -2 (in basic solution) Click here for answers