Air and Water
Water
Chemical tests:
- It turns white anhydrous copper (II) sulphate
- It turns blue cobalt chloride paper
Purification of water:
Uses: at home – drinking, cooking, washing (people, clothes, and dishes), in the toilet, on farms for animals or to water crops, in industry to dissolve, wash and cool things, and in power stations where steam is used to turn turbines.
Air
Clean air is approximately 79% nitrogen, 20% oxygen and the remainder is a mixture of noble gases, water vapour and carbon dioxide.
Common pollutants: carbon monoxide (from incomplete combustion of carbon-containing substances), sulphur dioxide (from combustion of fossil fuels containing sulphur compounds), nitrogen oxides (from hot furnaces and engines) and lead compounds (a lead compound is added to petrol to help it burn more smoothly).
Effects of pollutants: carbon monoxide – reacts with haemoglobin, preventing it from carrying oxygen – so you can die from oxygen starvation
Sulphur dioxide – irritates eyes and throat, causes respiratory problems and causes acid rain Nitrogen oxides – causes respiratory problems, forms acid rain.
Extraction of nitrogen and oxygen: fractional distillation of liquid air:
- Air is filtered to remove dust
- Water vapour and carbon dioxide removed, (because they would freeze and block the pipes):
-air is cooled until water vapour condenses
-then passes over absorbent beads to trap carbon dioxide
- It is compressed, causing it to heat Cooled by recycling cold air
- The cold compressed air is passed through a jet, into a larger It expands rapidly, making it very cold.
Steps 3 and 4 are repeated, cooling the air more. By -200°C it is liquid except for neon and helium. These gases are removed. They can be separated from each other by absorption on charcoal.
- The liquid air is pumped into the fractioning There it is slowly warmed up. The gases boil off one by one, and are collected in tanks or cylinders.
Nitrogen oxides are produced when oxygen and nitrogen from air react in hot conditions (in engines and furnaces). They are removed using a catalytic converter. Nitrogen oxides are decomposed back into nitrogen and oxygen.
Rust prevention: 1) coating with something to prevent contact with air and moisture (plastic, paint, grease, tin or chromium plating by electrolysis or galvanising (dipping in molten zinc)
- Sacrificial protection
- Anodising
Fertilisers: Nitrogen is needed for chlorophyll and other proteins. Potassium helps make proteins and resist diseases. Phosphorus helps roots grow and crops ripen.
All alkalis (except ammonia) will react with ammonium compounds, removing ammonia for example: calcium hydroxide
+ ammonium chloride → calcium chloride + water + ammonia.
Greenhouse gases: carbon dioxide and methane. They stop heat escaping in to space. Too much greenhouse gases leads to climate change. This will cause the ice poles to melt, rising sea levels, more droughts, storms, floods and famine.
Formation of carbon dioxide:
- Product of respiration
- COMPLETE combustion of carbon-containing substances
- Reaction of an acid and a
Sources of methane: oil and natural gas, decomposition of vegetation, and waste gases from digestion in animals. Sacrificial protection: a more reactive metal is used to coat a less reactive metal. The more reactive metal will react more easily and be sacrificed.
The Haber process: N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
Nitrogen comes from the air. Hydrogen can be made in several ways:
- Methane + steam → carbon dioxide + hydrogen
- it can be cracked (using a catalyst): C2H6 → C2H4 + H2 CONDITIONS: 450°C, 200atm, iron catalyst
The forward reaction is exothermic, and the backwards reaction is endothermic.
The optimum conditions would be high pressure, low temperature, removing ammonia as it forms. Higher temperature is used for a better rate and lower pressure for safety and it is cheaper. A catalyst is used for a faster rate.
The carbon cycle:
