1. Lecture 233/12/06

2. What is a REDOX reaction? OXIDATION: Ca(s)  Ca 2+ REDUCTION: 2H +  H 2 (g) OIL RIG Combined (net): REDOX REACTIONS Oxidation-Reduction Reaction REDOX REACTIONS Oxidation-Reduction Reaction

3. OXIDATION NUMBERS

4. Rules Atoms in elemental state Monatomic ions Reference elements Sum of all oxidation numbers OXIDATION NUMBERS What are they?

5. Oxidation number practice NH 3 N = ? H = ? ClO - Cl = ?O = ? H 3 PO 4 P = ?H = ?O = ? MnO 4 - Mn = ?O = ? Cr 2 O 7 2- Cr = ?O = ? C 3 H 8 C = ?H = ?

6. How do you know if the reaction is a Redox Reaction?

7. Balancing Redox reactions H 2 C 2 O 4 (aq) + MnO 4 -  Mn 2+ + CO 2 (g) oxalic acid permanganate 1. Break into half-reactions 2. Balance the atoms 3. Combine the half-reactions 4. Check for mass and charge balance

8. Redox example: respiration/combustion Balance redox reaction for glucose (C 6 H 12 O 6 ) respiration (same as combustion reaction) How do the oxidation numbers of carbon and oxygen change? What is being oxidized? What is being reduced? What is the oxidizing agent? The reducing agent?

9. Redox reaction example

10. Redox under basic conditions: Balance the following redox reaction in a basic solution CrO 4 2- + SO 3 2-  Cr(OH) 3 + SO 4 2-

11. Displacement reactions Some metals react with acids to produce salts and H 2 gas Balance the following displacement reaction: Zn (s) + HBr (aq)  ZnBr 2 (aq) + H 2 (g)

12. Apparatus with oxidation and reduction reactions in different compartments Apparatus with oxidation and reduction reactions in different compartments redox reaction occurs by transferring electrons through an external connector redox reaction occurs by transferring electrons through an external connector voltaic or galvanic cell product favored reaction product favored reaction produces electric current produces electric current electrolytic cell reactant favored reaction reactant favored reaction external electric current used to drive reaction external electric current used to drive reaction Electrochemical cells

13. Voltaic (Galvanic) Cells Redox reaction must favor products Electrodes Anode: where oxidation occurs Cathode: where reduction occurs Salt bridge Need salt bridge or porous barrier in order to maintain charge balance in each compartment External circuit Wire to allow electrons to flow between electrodes