Air and water
Measuring the percentage of oxygen in air
Results:
● Starting volume of air: 100cm
3
● Final volume of air: 79cm
3
● The percentage of oxygen is therefore 21/100 x 100 = 21%
Separating gases from air
- First air must be cooled until it turns liquid
- Then the liquid is allowed to warm up again. The various gases boil off at different temperatures
Uses
Oxygen
- Converting impure iron to steel
- Oxygen masks in hospitals
- Oxy-acetylene to cut steel
Nitrogen
- Freeze food in food factories
Noble gases
- Argon in bulbs
- Neon in advertising signs
- Helium in balloons
Pollutants of air
Pollutant
Source
Effect
Control
Carbon monoxide
Incomplete combustion
of carbon containing
fuels
Toxic
Catalytic converter
Oxides of nitrogen
Nitrogen and oxygen
Acid rain
Catalytic converter
from air react at high
temperature in car,
furnace or lighting
Sulfur dioxide
Burning of fossil fuels
containing sulfur
Acid rain
Flue gas desulfurisation
Lead compounds
Burning leaded petrol
Nervous disorder,
learning disability in
children
Stop using leaded petrol
- Effects of acid rain
- Lakes and soils acidified
- Nutrient leached out from soil, trees, crops causing reduction in growth
- Kills marine life
Catalytic converters
Car exhaust fumes contain gases such as:
- Carbon monoxide CO
2
- Oxides of nitrogen NO, NO
2
- Unburned hydrocarbons
● Reduction reaction: 2NO → N
2
+ O
2
● Oxidation reactions: 2CO + O
2
→ 2CO
2
● Other: NO + CO → N
2
+ CO
2
- A catalytic converter therefore ‘removes’ polluting oxides and completes the oxidation of unburned
hydrocarbon fuel
- honeycombed surface on which gases can react
Rust
Rusting of iron and steel is an oxidation process where the iron gets oxidised to iron oxide
Conditions necessary for rusting are oxygen and water
Conditions that speed up rusting are warmth and salinity
Rust prevention
→ paint
→ grease
→ electroplating with chromium, nickel, cobalt, copper or tin
→ alloying by converting iron into stainless steel
→ galvanising
→ sacrificial protection
