1. Lecture 233/30/05

2. Redox example: respiration/combustion Balance redox reaction for glucose (C 6 H 12 O 6 ) respiration (same as combustion reaction) C 6 H 12 O 6 + 6H 2 O  6 CO 2 + 24H + + 24e - 4e - + 4H + + O 2  2H 2 O C 6 H 12 O 6 + 6O 2  6 CO 2 + 6H 2 O How does the oxidation numbers of carbon and oxygen change? What is being oxidized? What is being reduced? What is the oxidizing agent? The reducing agent?

3. Redox under basic conditions: Solve Redox equation, then add OH - to both sides to cancel H + Balance the following redox reaction in a basic solution CrO 4 2- + SO 3 2-  Cr(OH) 3 + SO 4 2- 3e - + 5H + + CrO 4 2-  Cr(OH) 3 + H 2 O H 2 O + SO 3 2-  SO 4 2- + 2H + + 2e - 4H + + H 2 O + 2CrO 4 2- + 3SO 3 2-  2Cr(OH) 3 + 3SO 4 2- 4OH - + 4H + + H 2 O + 2CrO 4 2- + 3SO 3 2-  2Cr(OH) 3 + 3SO 4 2- + 4OH - 5H 2 O + 2CrO 4 2- + 3SO 3 2-  2Cr(OH) 3 + 3SO 4 2- + 4OH -

4. Displacement reactions Some metals react with acids to produce salts and H 2 gas special redox type of displacement reaction We will soon see why some metals react like this and some don’t Balance the following displacement reaction: Zn (s) + HBr (aq)  ZnBr 2 (aq) + H 2 (g) Zn (s) + 2HBr (aq)  ZnBr 2 (aq) + H 2 (g)

5. 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

6. 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