water

1) Describe chemical tests for Water
  • Blue Cobalt(II) Chloride Paper: Paper turns from blue to pink.
  • Anhydrous Copper(II) Sulphate powder: From white powder to blue ​crystals.
2) Describe Treatment of Water
  • Water is essential for life. It must be free of poisonous salts and harmful microbes.
  • ​Water is pumped through screens to remove solid floating debris.
  • Aluminum sulfate is added to coagulate (stick together) small pieces of clay so that they are easily removed.
  • The water is then filtered by passing through coarse sand to remove larger insoluble solids.
  • The water is then sterilized to kill microbes by using ozone, UV light or chlorine.
  • Some countries also add fluorine.

air

3) Composition of Air
  • 78% nitrogen
  • 21% oxygen
  • Rest is mixture of noble gases, water vapour and carbon dioxide.
4) Name Common Pollutants
Pollutant
Source
Problems caused
Carbon Monoxide
CO
Incomplete combustion of carbon-containing substances
Reacts with haemoglobin, preventing it from carrying oxygen; death due to oxygen starvation
​Sulphur Dioxide
SO2
From combustion of fossil fuels which contain sulfur compounds
Irritates eyes and throat, causes respiratory problems and causes acid rain
Oxides of Nitrogen
NOx
From car exhausts
Causes respiratory problems and forms acid rain
5) Approaches to Reduce Air Pollution
Reduce emission of sulfur dioxide:
  • Use low sulfur petrol.
  • Flue gas desulfurisation by calcium oxide.

​Reduce pollution from vehicles:
  • ​In the combustion engine, insufficient amounts of oxygen lead to incomplete combustion of the fuel.
  • Gases produced: (a) carbon monoxide (b) oxides of nitrogen.
  • A catalytic convertor removes nitrogen monoxide and carbon monoxide from exhaust emissions by reaction over a hot catalyst.​
\[2CO+O_{2}\rightarrow 2CO{2}\]
\[2NO+2CO\rightarrow N_{2}+2CO_{2}\]
\[2NO\rightarrow N_{2}+O_{2}\]
6) Methods of Rust Prevention
  • Rusting of iron requires presence of oxygen and water.

Coating with something to prevent contact with air and moisture will prevent rusting (barrier methods):
  • Plastic, paint and grease.
  • Electroplating with tin or chromium.
  • Galvanising: dipping in molten zinc.​

carbon dioxide and methane

7) Formation of Carbon Dioxide
  • as a product of complete combustion of carbon-containing substances.
  • as a product of respiration.
  • as a product of the reaction between an acid and a carbonate.
  • as a product of thermal decomposition of calcium carbonate.
8) Greenhouse Gases
  • Greenhouse gases are 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; global warming.

nitrogen and fertilisers

9) Describe the need for Fertilisers
  • Fertilisers contain nitrogen, potassium and phosphorus.
  • Nitrogen promotes healthy leaves, potassium promotes growth and healthy fruit and flowers and phosphorus promotes healthy roots.​
10) Describe the Displacement of Ammonia from its Salts
  • Ammonia can be displaced from its salts by the addition of an alkali substance.
  • Farmers regularly add basic substances such as calcium hydroxide to their soil to neutralise any excess soil acidity.
  • If too much is added, then an ammonia displacement reaction may occur.
  • This involves the loss of nitrogen from the fertiliser, nullifying its effectiveness as a fertiliser.
11) Explain the manufacture of Ammonia by the Haber process
\[N_{2}(g)+3H_{2}(g)\leftrightharpoons 2NH_{3}(g)\]
Raw materials
  • Nitrogen: from the air
  • Hydrogen: methane + steam → carbon dioxide + hydrogen
 
Essential conditions:
  • Temperature: 450°C
  • Pressure: 200 atm
  • Catalyst: Iron