Gases in the air and rusting (TOPIC 14)

Argon - 1% Nitrogen - 78% Carbon dioxide - 0.04% Oxygen - 21%

Using iron and phosphorus

Soak iron wool in acetic acid(catalyst) Put wool in measuring cylinder and invert it in a beaker of water. Record starting position of water in the cyclinder. Water level will rise as iron reacts with oxygen in the air. Water takes up space where oxygen was. Leave for 7 days. Record finishing position of water Change in volume / start volume X 100 Or use phosphorus with gas syringes ensuring one is empty and one is full

Start volume - final volume / start volume X 100

Place phosphorus in tube and attach glass syringe at either end. Make sure one is empty and the other one is full. Heat the phosphorus and move the air over it back and forth using the syringes Air will decrease - phosphorus oxide Use percentage of oxygen in air formula to calculate

2Mg + o2 -> 2MgO (Magnesium Oxide) Burns with a bright white flame. Forms white magnesium oxide powder Magnesium oxide is alkaline when dissolved in water

2H2 + O2 -> 2H2O Burns easily produces pale blue flame Produces water vapour so is a neutral PH

S + O2 -> SO2 (Sulfur dioxide) Burns with pale blue flame Sulfur dioxide is acidic when dissolved in water

Metal carbonate -> Metal oxide + Carbon Dioxide

Copper carbonate -> Copper oxide + Carbon dioxide Copper carbonate = green solid Copper oxide = black solid

Iron in the presence of Oxygen + Water Forming Hydrated Iron oxide

Barrier methods Galvanizing Sacrificial Protection

Barrier methods - preventing oxygen and water from touching the iron. Do this through painting (for big pieces) Oil or grease - for moving parts Electroplating - Uses electrolysis to cover iron in thin layer of another metal

Coating iron in zinc - acts as barrier method prevents water and oxygen reaching metal. But also if oxygen does reach metal it reacts with zinc instead.

Adding a more reactive metal to iron so if the object gets exposed to oxygen. That sacrificial metal is oxidised and not the iron