4.1 Rocks
Rocks containing calcite Rocks containing calcite (CaCO(CaCO33))
limestonelimestone
4.1 Rocks
chalkchalk
4.1 Rocks
marblemarble
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(limestone) (chalk) (marble)
CalciteCaCO3
contains
Formed by skeletons and shells of sea animals sank to the bottom of the sea, covered by mud under heat and pressure for millions of years
4.1 Rocks
Limestone
It is the most common form of calcium carbonate.
It is hard and strong, yet inexpensive.
It is widely used in the building industry.
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Fig. 4.9 Spectacular limestone pinnacles rise along both sides of the Li River in Guilin, China.
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Uses of limestoneUses of limestone1. To make footpath.
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2. A raw material for making cement.
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Chalk
Fig. 4.10 Chalk cliffs in Sussex, England.
Chalk is slightly softer and is also used in buildings.
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MarbleMarble is a crystalline solid and is very hard.
It can be smoothly polished to give a beautiful appearance.
It is often used for building statues, monuments, and as floors and walls in some buildings.
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(limestone)
(chalk) (marble)
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Weathering and erosion Weathering and erosion
Fig. 4.15 The Great Wall of China has been continuously weathered during the past 2200 years.
All rocks exposed on the Earth’s surface are slowly worn away by weathering and erosion.
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Fig. 4.16(a) Wind erosion caused this unusual limestone formation.
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Fig. 4.16(b) A sea cliff in Hong Kong — a result of water erosion.
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Types of weatheringTypes of weathering
Rocks can be weathered in two ways:• Physical weathering• Chemical weathering
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Rocks break!
2. Rocks cool down quickly at night
1. Rocks get hot in the daytime
Physical weatheringPhysical weathering
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Fig. 4.17 Rocks in deserts are badly weathered, partly due to big day-and-night temperature change.
4.1 Rocks
Chemical weatheringChemical weathering
CaCO3 (s) + H2CO3 Ca(HCO3)2 (aq)
CO2 + H2O H2CO3
Carbon dioxide in air dissolves slightly in rainwater, forming an acidic solution:
The carbonic acid formed reacts with calcium carbonate:
Attack by acid
Calcium hydrogencarbonate is soluble in water and thus the limestone is slowly worn away.
(acidic)
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Earth’s crust
RocksRocks
containing ________
Marble
calcite
broken down intosmall pieces
transportedaway bygravity, windand water
Weathering Erosion
Limestone Chalk
Physical Chemical
Attacked bycarbonic acid
4.1 Rocks
Thermal decomposition of Thermal decomposition of calcium carbonatecalcium carbonate
CaCO3CaCO3
gently
warmed
No visible change
CaO CO2
heated strongly
4.1 Rocks
calcium carbonate
roaring non-luminous flame
Bunsen burner
test tube holder
Fig. 4.23 Heating calcium carbonate strongly to make quicklime (calcium oxide).
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H2O
heatCaO (s)
(quicklime)
Ca(OH)2 (S)
(slaked lime)
4.1 Rocks
water
Ca(OH)2 (S)
(slaked lime)
LimewaterCa(OH)2(aq)
filtered whitesuspension
4.1 Rocks
Limewater test for Limewater test for carbon dioxidecarbon dioxide
limewater(colourless solution)
Limewater is a saturated solution of calcium hydroxide in water.
It is a clear colourless solution.
4.1 Rocks
When carbon dioxide is passed through limewater for a few seconds…
limewater turned milky
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Carbon dioxideCarbon dioxide
Calcium hydroxide
(colourless solution)
water
Carbon dioxide is a colourless gas. It turns limewater milky.
(white solid)
Calciumcarbonate
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Carbon dioxideCarbon dioxide
Calcium hydrogencarbonate
(colourless solution)
water
(white solid)
Calciumcarbonate
4.1 Rocks
Some chemical changes involving calcium carbonate are related.
CaCOCaCO33
Ca(OH)Ca(OH)2 (aq)2 (aq)CaOCaO
Ca(OH)Ca(OH)2 (s)2 (s)
pass in CO2 (limewater test)
add more H2O, stir well and then filter
strong heat
add a little H2O
step 1
step 2step 3
step 4
(limewater)
(limestone)
(slaked lime)
(quicklime)
CO2 given off
4.1 Rocks
How can we show How can we show that limestone, that limestone, chalk and marble chalk and marble all contain all contain calcium calcium ionsions and and carbonate carbonate ionsions??
????
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Test for calcium Test for calcium ionsions
Calcium compounds give a brick-red flame in a flame test.
4.1 Rocks
Test for carbonate ionsTest for carbonate ions
Fig. 4.27 Test for a carbonate ions by limewater test.
dilute hydrochloric acid
solid sample under test
limewater
delivery tube
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hydrochloric acid
Calciumcarbonate
Calcium chloride
Carbon dioxideCarbon dioxide
water
4.1 Rocks
Limestone, chalk and marble all give a positive limewater test.
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Calcium carbonate
Carbonate ions
________flame colourBrick-red
flame test addhydrochloricacid
Carbon dioxide
Calcium ions
4.1 Rocks
Some chemical changes involving calcium carbonate are related.
CaCOCaCO33
Ca(OH)Ca(OH)2 (aq)2 (aq)CaOCaO
Ca(OH)Ca(OH)2 (s)2 (s)
pass in CO2 (limewater test)
add more H2O, stir well and then filter
strong heat
add a little H2Or
step 1
step 2step 3
step 4
(limewater)
(limestone)
(slaked lime)
(quicklime)
CO2 given off
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Earth’s crust
RocksRocks
containing ________
Marble
calcite
broken down intosmall pieces
transportedaway bygravity, windand water
Weathering Erosion
Limestone Chalk
Physical Chemical
Attacked bycarbonic acid
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Calcium carbonate
Carbonate ions
________flame colourBrick-red
flame test addhydrochloricacid
Carbon dioxide
Calcium ions
