Summary notes for CIE IGCSE Biology Topic 11: Air and water
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Course
Chemistry
Institution
GCSE
Complete revision notes for Topic 11 of the CIE IGCSE Chemistry course: Air and water. Explanations with diagrams for every specification point. These notes are written for candidates taking the Extended paper.
Describe chemical tests for water using cobalt(II) chloride and copper(II) sulphate
Cobalt (II) chloride
Cobalt (II) chloride turns blue to pink on the addition of water. This test is usually done using
cobalt chloride paper.
The equation is: CoCl2(s) + 6H2O(l) → CoCl2.6H2O(s)
Copper (II) sulphate
Anhydrous copper (II) sulphate turns white to blue on the addition of water
The equation is: CuSO4(s) + 5H2O(l) → CuSO4.5H2O(s)
Describe, in outline, the treatment of the water supply in terms of filtration and chlorination
Untreated water contains soluble and insoluble impurities:
Insoluble impurities include soil, pieces of plants and other organic matter
Soluble impurities include dissolved calcium, metallic compounds and inorganic
pollutants
For this reason, water purification involves a two-step process:
1) Filtration
2) Chlorination
Filtration
Filtration is the process used to remove large insoluble particles by passing the water
through layers of sand and gravel filters that trap larger particles.
Chlorination
But bacteria and other microorganisms are too small to be trapped by the filters, so
chlorination is used.
This involves the careful addition of chlorine to the water supply which kills bacteria and
other unwanted microorganisms.
Cholera and typhoid are examples of bacterial diseases which can arise by the consumption
of untreated water.
, Name some of the uses of water in industry and in the home
Industry
As a coolant to reduce the temperature of some industrial processes e.g., in nuclear power
plants
Watering crops
As a solvent in many chemical production processes
Hydroelectric power stations to generate electricity
As a first raw material for many processes e.g., the production of ethanol from ethene and
steam (water)
Home
Drinking, cooking and washing
General sanitation
In car radiators, for gardens and plants
Discuss the implications of an inadequate supply of water, limited to safe water for drinking
and water for irrigating crops
Clean and safe water supply is very important to mankind.
Many problems arise in the event of an inadequate water supply, including:
Food shortages and famine due to a lack of crops which cannot grow without a clean
water supply
Poor sanitation leads to the spread of bacteria and disease as drinking water
becomes infected
11.2 Air
State the composition of clean, dry air as being approximately 78% nitrogen, 21% oxygen
and the remainder as being a mixture of noble gases and carbon dioxide
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