Gases in the air and rusting (TOPIC 14) Flashcards
What are the 4 main gases in the atmosphere
Percentages?
Argon - 1%
Nitrogen - 78%
Carbon dioxide - 0.04%
Oxygen - 21%
How can we determine the percentage of oxygen in the air?
Using iron
and phosphorus
Percentage of oxygen in the air iron experiment.
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
Formula for percentage of oxygen in the air?
Start volume - final volume / start volume X 100
How do we use phosphorus to determine the percentage of oxygen in the air?
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
Combustion of magnesium in oxygen?
2Mg + o2 -> 2MgO (Magnesium Oxide)
Burns with a bright white flame.
Forms white magnesium oxide powder
Magnesium oxide is alkaline when dissolved in water
Combustion of Hydrogen in oxygen?
2H2 + O2 -> 2H2O
Burns easily produces pale blue flame
Produces water vapour so is a neutral PH
Combustion of sulfur in oxygen?
S + O2 -> SO2 (Sulfur dioxide)
Burns with pale blue flame
Sulfur dioxide is acidic when dissolved in water
Thermal decomposition of metal carbonates?
Metal carbonate -> Metal oxide + Carbon Dioxide
Thermal decomposition of copper carbonate
Copper carbonate -> Copper oxide + Carbon dioxide
Copper carbonate = green solid
Copper oxide = black solid
What are the conditions for rusting?
Iron in the presence of Oxygen + Water
Forming Hydrated Iron oxide
How do we prevent rusting?
Barrier methods
Galvanizing
Sacrificial Protection
What are the barrier methods to prevent rusting
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
How does galvanisation prevent rusting?
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.
How does sacrificial protection prevent rusting?
Adding a more reactive metal to iron so if the object gets exposed to oxygen.
That sacrificial metal is oxidised and not the iron