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:
Reduce pollution from vehicles:
- 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
Essential conditions:
- Nitrogen: from the air
- Hydrogen: methane + steam → carbon dioxide + hydrogen
Essential conditions:
- Temperature: 450°C
- Pressure: 200 atm
- Catalyst: Iron