CIE IGCSE Chemistry Revision Notes
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2 ORGANISATION
OF THE ORGANISM
13 CARBONATES
YOUR NOTES
CONTENTS:
13.1 CARBONATES 3 CARBONATES
VIEW EXAM QUESTIONS
13.1 CARBONATES
Calcium Oxide & Calcium Carbonate
Manufacture of lime
• Limestone consists mainly of calcium carbonate, CaCO3
• Lime which is calcium oxide, is manufactured from calcium carbonate by thermal
decomposition:
CaCO3 → CaO + CO2
• Slaked lime, calcium hydroxide, is made by adding a small amount of water slowly to
calcium oxide:
CaO + H2O → Ca(OH)2
• Limewater is a solution of calcium hydroxide in water, hence it is alkaline
• The addition of carbon dioxide to calcium hydroxide produces the initial starting material,
calcium carbonate:
CO2 + Ca(OH)2 → CaCO3 + H2O
• This reaction is the basis of the standard chemical test for CO2
Ca(OH)2 solution turns cloudy when in the presence of CO2 gas due to the
formation of insoluble white calcium carbonate
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13 CARBONATES
YOUR NOTES
13.1 CARBONATES cont...
The combination of these three reactions constitutes the limestone cycle:
Diagram showing the stages in the limestone cycle
Uses of limestone and limestone products
• Limestone (calcium carbonate) is used in the manufacture of iron and cement
• In the production of iron, limestone is added to the blast furnace where it decomposes to
form lime (CaO) and carbon dioxide
• The lime reacts with silica impurities to form calcium silicate, which floats to the top of the
molten iron and is removed:
CaO + SiO2 → CaSiO3
• Cement is manufactured by heating a mixture of powdered limestone and clay in a rotary
kiln
• Once heated, calcium sulfate and water are added which produce cement
• Cement is a hardened, interlocked structure of calcium aluminate (Ca(AlO2)2 and calcium
silicate (CaSiO3)
• CaCO3 is also used in treating excess acidity in soils and lakes where it is often preferred
to lime because it does not make the water in the soil alkaline
• Lime (calcium oxide) is used in lime mortar and in flue-gas desulfurization
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2 ORGANISATION
OF THE ORGANISM
13 CARBONATES
YOUR NOTES
13.1 CARBONATES cont...
• Flue-gas desulfurization involves spraying acidic sulfur dioxide emissions with jets of
slaked lime to reduce pollution by neutralising these gases before they leave the factory
chimneys
• Lime is also used in treating excess acidity in soils and lakes. If excess lime is used,
however, the water in the soil may become too alkaline
• Slaked lime (calcium hydroxide) is used in treating acidic soils and neutralising acidic
industrial wasted products
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13 CARBONATES
YOUR NOTES
EXAM QUESTIONS
?
QUESTION 1
A solid compound WX is heated to a high temperature and produces solid
compound Y and gas Z. No other reagent is used.
WX(s) → Y(s) + Z(g)
What type of reaction has occurred?
A Neutralisation reaction
B Redox reaction
C Thermal decomposition reaction
D Metal displacement reaction
?
QUESTION 2
A student is given a solid compound X to analyse. The student heats the solid
and observes a colour change from green to black. A gas is released which
turns limewater cloudy.
What is the solid compound and the gas produced?
X
gas
A
copper carbonate
carbon dioxide
B
copper carbonate
oxygen
C
calcium carbonate
carbon dioxide
D
calcium carbonate
oxygen
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2 ORGANISATION
OF THE ORGANISM
13 CARBONATES
YOUR NOTES
EXAM QUESTIONS
?
QUESTION 3
In which of the following processes is carbon dioxide not a product?
A Addition of lime to acidic soil
B Producing lime from limestone
C Respiration
D Fractional distillation
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