C13.1CALCIUM CARBONATE
Calcium carbonate (CaCO3) is an important raw material which occurs naturally as the sedimentary rocks, limestone and chalk, and as the metamorphic rock, marble. These rocks are obtained by quarrying.
Malham cove (limestone) Dover cliffs (chalk) marble quarry
Thermal Decomposition When some substances are heated, they decompose (break down) into simpler substances. This process is called THERMAL DECOMPOSITION. Calcium carbonate undergoes thermal decomposition when heated in a kiln to about 1100oC, forming calcium oxide (quicklime) and carbon dioxide. Other metal carbonates decompose in a similar way. The lower the metal is in the reactivity series, the lower the temperature at which this decomposition takes place. CaCO (s) CaO(s) + CO (g) 3 2
. We can test for the production of CO gas using limewater. If 2 CO is given off the limewater 2 will turn cloudy and decomposition has occurred
When CO2 reacts with limewater the following reaction occurs which produces a white insoluble precipitate (which makes it cloudy)
Ca(OH)2 (aq) + CO2 (g) CaCO3(s) + H2O (l)
Calcium hydroxide + carbon dioxide Calcium carbonate + water (limewater)
TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 1 Hydration Quicklime reacts with water in a very exothermic reaction, forming calcium hydroxide (slaked lime). CaO(s) + H O(l) Ca(OH) (s) 2 2
The Limestone Cycle
LIMESTONE (calcium carbonate) H2O
CO2
CO2
SLAKED LIME QUICKLIME (calcium hydroxide) (calcium oxide)
H2O
TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 2 Building Material Limestone is used as a building material. A form of limestone, called Portland stone, was used in the construction of St Paul’s Cathedral in London. Limestone is a hard rock, but it erodes badly in polluted urban environments, because it dissolves readily in acids. Marble is used in sculpture and as a building material.
Removal of Acidity Powdered limestone is used to neutralise acidity in lakes and in light, sandy soils. Slaked lime (calcium hydroxide) is used to neutralise acidity in heavy soils and in drinking water.
Glass Manufacture Glass is made by heating a mixture of: limestone sand sodium carbonate
Iron production Limestone is added to the Blast Furnace, in the production of iron, to remove acidic impurities present in iron ore.
Cement Manufacture Cement is made by roasting powdered limestone with powdered clay in a rotary kiln.
Mortar which is used to build a modern house today is a mixture of cement, sand and water.
The hard, stone-like building material, concrete is made by mixing: cement water sand crushed rock
The soft mixture undergoes a slow chemical reaction and eventually sets hard. TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 3 END-OF-TOPIC TEST 1. Which oxide can be reduced by heating it with carbon?
A aluminium oxide B calcium oxide C copper(II) oxide D potassium oxide
2. A student suggests three uses of calcium carbonate (limestone).
1 manufacture of cement 2 manufacture of iron 3 treating alkaline soils Which of these suggestions are correct?
A 1 and 2 only B 1 and 3 only C 2 and 3 only D 1, 2 and 3
3. A steel works and a chemical works are built near to a city. The limestone buildings in the city begin to crumble. Which gas is most likely to cause this damage?
A carbon dioxide B carbon monoxide C oxygen D sulphur dioxide
4. A newspaper article claims that carbon dioxide is formed as follows.
1 during respiration 2 when calcium carbonate reacts with hydrochloric acid 3 when methane burns in air
Which statements are correct?
A 1, 2 and 3 B 1 and 2 only C 1 and 3 only D 2 and 3 only
5. What are the products when limestone (calcium carbonate) is strongly heated?
A calcium hydroxide and carbon dioxide B calcium hydroxide and carbon monoxide C calcium oxide and carbon dioxide D calcium oxide and carbon monoxide
6.Two processes are listed.
1 treating acidic soil with slaked lime TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 4 2 using limestone to extract iron
In which of these processes is carbon dioxide produced?
7. Which of the oxides CaO, CuO and Na2O can be reduced by heating with carbon?
A CaO only B CuO only C Na2O only D CaO, CuO and Na2O
8. Dolomite is a rock that contains magnesium carbonate.
A piece of dolomite is heated strongly in air.
Which word equation correctly describes the reaction that takes place?
9. In which process is carbon dioxide not formed?
A blast furnace extraction of iron B burning of natural gas C heating lime D oxy-acetylene welding
10. A newspaper article claims that carbon dioxide is formed as follows.
1 during respiration 2 when calcium carbonate reacts with hydrochloric acid 3 when methane burns in air
Which statements are correct?
A 1, 2 and 3 B 1 and 2 only C 1 and 3 only D 2 and 3 only 11. In separate experiments, mixtures of CuO/C and of MgO/C are strongly heated in the apparatus shown.
TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 5 What happens to the limewater in these experiments?
12. The diagram shows a kiln used to heat limestone.
What is the product and what waste gas is formed?
TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 6 B1.. Give the names of two naturally occurring forms of calcium carbonate, one a sedimentary rock, the other a metamorphic rock.
Sedimentary ...... ………....
Metamorphic ...... ………...
Complete this sentence: When calcium carbonate is heated strongly, it undergoes a chemical reaction called ...... and forms a gas called ...... and a solid called ...... ……......
This solid is also known as ......
Describe what you would see when water is added to this solid.
...... ………...
2. How is calcium carbonate turned into cement?
...... ………....
Which other substances are added to cement to make concrete?
...... ………...
State THREE uses for calcium carbonate, other than in cement-making.
...... …..
...... ….
...... …
TOPIC 10.1.2: ROCKS & BUILDING MATERIALS 7