1. OXIDATION
ANY REACTION IN WHICH A SUBSTANCE LOSES ELECTRONS
IRON LOSES ELECTRONS TO OXYGEN DURING RUSTING

2. REDUCTION
ANY REACTION IN WHICH A SUBSTANCE GAINS ELECTRONS
OXYGEN GAINS ELECTRONS FROM IRON DURING RUSTING

3. EXAMPLE REACTION
Zn + O → Zn+2 + O-2
ZINC LOSES 2 ELECTRONS AND IS OXIDIZED
OXYGEN GAINS 2 ELECTRONS AND IS REDUCED

4. HALF REACTIONS
SHOW THE OXIDATION OR REDUCTION SEPARATE FROM THE OTHER
Zn → Zn e-
O + 2e- → O-2

5. OXIDATION-REDUCTION REACTION
CALLED A REDOX REACTION
ALSO CALLED A GALVANIC PROCESS

6. OXIDATION II
MAKES ELECTRONS AVAILABLE
THE RELEASED ELECTRONS FLOW TO FORM A CURRENT

7. OXIDATION III
THE AMOUNT OF CURRENT IS RELATED TO HOW STRONGLY ATOMS HOLD VALENCE e-
DIFFERENT FOR EACH ELEMENT

8. OX IV
ELECTRONS WILL FLOW FROM AN ELEMENT THAT GIVES THEM UP EASILY TO ONE THAT DOES NOT GIVE THEM UP EASILY
THIS CAUSES AN ELECTRIC CURRENT

9. POTENTIAL DIFFERENCE
FORCE PUSHING ELECTRONS IN A CURRENT
CALLED VOLTAGE

10. GALVANIC CELL
A DEVICE CONTAINING SUBSTANCES THAT UNDERGO AN REDOX REACTION AND PRODUCE A VOLTAGE

11. ALSO CALLED VOLTAIC CELL

12. GALVANIC CELL II
SUBSTANCES ARE SEPARATED
REACTION TAKES PLACE WHEN THE SUBSTANCES ARE CONNECTED WITH A CONDUCTOR

13. PARTS OF A CELL
CATHODE IS THE PLACE WHERE REDUCTION OCCURS (ELECTRONS FLOW TO IT)
CATHODE IS POSITIVE

14. PARTS OF A CELL II
ANODE IS THE PLACE WHERE OXIDATION OCCURS (ELECTRONS FLOW FROM IT)
IT IS NEGATIVE

15. ELECTROLYTE – SUBSTANCE THAT ALLOWS IONS TO MOVE IN THE CELL

16. BATTERY
A SERIES OF GALVANIC CELLS (SOME ARE ONLY 1 CELL)
DRY CELLS USE MOIST ELECTROLYTES RATHER THAN LIQUID ONES

17. CARBON DRY CELL
GRAPHITE ROD SURROUNDED BY MOIST MnO2 – CARBON PASTE IS THE CATHODE
ZINC ANODE (CASE)
MOIST NH4Cl AND ZnCl2 ELECTROLYTE

18. DRY CELL II
Mn IS REDUCED
REACTION PRODUCES AMMONIA GAS THAT CAUSES BATTERY TO EXPAND
ELECTROLYTE IS ACIDIC

19. ALKALINE DRY CELL
CATHODE IS A MOIST PASTE OF MnO2 AND GRAPHITE
ANODE IS MOIST PASTE OF ZINC AND KOH AROUND A BRASS COLLECTOR

20. ALKALINE VS. CARBON
HAS LONGER SHELF LIFE THAN CARBON DRY CELL
LESS ACIDIC
NO AMMONIA GAS
MORE RELIABLE OPERATING LIFE

21. LEAD STORAGE BATTERY
ANODE IS LEAD METAL
CATHODE IS PbO2
ANODE IS OXIDIZED TO Pb+2
CATHODE IS REDUCED FROM Pb+4 TO Pb+2

22. LEAD STORAGE II
Pb+2 COMBINES WITH SO4-2 FROM SULFURIC ACID ELECTROLYTE TO FORM PbSO4

23. APPLYING A VOLTAGE TO THIS BATTERY CAUSES PbSO4 TO REACT WITH WATER TO FORM PbO2 AND Pb

24. NICKEL-CADMIUM BATTERY
ANODE IS CADMIUM
CATHODE IS NiO2
ELECTROLYTE IS KOH SOLUTION

25. CORROSION
A NATURAL GALVANIC PROCESS (REDOX REACTION)
OCCURS WHEREVER ACTIVE METALS ARE IN CONTACT WITH SUBSTANCES THAT CAN OXIDIZE THEM

26. RUST
OXIDATION OF IRON BY OXYGEN IN THE PRESENCE OF WATER
WATER IS THE ELECTROLYTE
ANODIC RXN: Fe → Fe+2 + 2e-

27. MANY CATHODIC REACTIONS

28. RUST II
OVERALL: 2Fe + 3O2 → 2Fe2O3

29. CORROSION INHIBITORS
SUBSTANCES THAT SLOW THE RATE OF ELECTRON TRANSFER FROM THE OXIDIZED SUBSTANCE
ADDED TO CAR COOLING SYSTEM – STICK TO IRON SURFACE

30. INHIBITORS II
EXAMPLES: CERTAIN PHOSPHATES, CHROMATES, AND ORGANIC COMPOUNDS
PAINT CONTAINING RED LEAD (Pb3O4) OR ZINC CHROMATE (ZnCrO4) WORK WELL

31. CATHODIC PROTECTION
PUT A MORE ACTIVE METAL IN CONTACT WITH METAL TO BE PROTECTED
ZINC OR MAGNESIUM IS OFTEN USED

32. THEY OXIDIZE INSTEAD OF THE PROTECTED METAL

33. GALVANIZED IRON
COATED WITH A ZINC COMPOUND TO PROVIDE CATHODIC PROTECTION