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

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

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

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

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

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

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

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

POTENTIAL DIFFERENCE FORCE PUSHING ELECTRONS IN A CURRENT CALLED VOLTAGE

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

ALSO CALLED VOLTAIC CELL

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

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

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

ELECTROLYTE – SUBSTANCE THAT ALLOWS IONS TO MOVE IN THE CELL

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

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

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

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

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

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

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

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

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

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

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

MANY CATHODIC REACTIONS

RUST II OVERALL: 2Fe + 3O2 → 2Fe2O3

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

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

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

THEY OXIDIZE INSTEAD OF THE PROTECTED METAL

GALVANIZED IRON COATED WITH A ZINC COMPOUND TO PROVIDE CATHODIC PROTECTION