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Topic 1 The Planet EarthTopic 1 The Planet Earth
Unit 4 Rocks and mineralsUnit 4 Rocks and minerals
Jing Kung Educational Press All Rights Reserved
2Unit 4 Rocks and minerals
4.2 Extracting metals from their ores
4.3 Investigating calcium carbonate
4.4 Formation of chalk, limestone and marble
4.5 Formation of limestone caves
Key terms
4.1 Metals in the Earth’s crust
Summary
Content
Unit key concept
Unit 4 Rocks and minerals 3
Unit Key Concepts
Metals in the Earth’s crust Methods for extracting metals from
their ores Chemical reactions of calcium carbonate Formation of chalk, limestone and marble
4Unit 4 Rocks and minerals
Metals play a very important role in our lives.
4.1 Metals in the Erath’s crust (p. 66)
A mirror with a film of silver on the back of a sheet of glass.
6Unit 4 Rocks and minerals
4.1 Metals in the Erath’s crust (p. 66)
Some metals are obtained from the oceans, but most metals are obtained from the Earth’s crust.
About 25% of the Earth’s crust consists of metals. Only a few metals, such as gold and silver, exist as free
elements in the Earth. Most of them exist as compounds in nature.
The individual chemical compounds that make up rocks are called minerals (礦物 ). Rocks from which we obtain metals are called ores (礦石 ).
Ores of aluminium, copper, iron and zinc (from left to right)
7Unit 4 Rocks and minerals
Getting a metal from its ore is called extracting (提取 ) the metal.
4.2 Extracting metals from their ores (p. 67)
Metal Name of ore Main metallic compound in the ore
Aluminium bauxite (鋁土礦 ) an oxide of aluminium
Iron haematite (赤鐵礦 ) an oxide of iron
Mercury cinnabar (硃砂 ) A sulphide of mercury
The names of common ores of three metals and the main metallic compound each ore contains:
8Unit 4 Rocks and minerals
Physical methods
Only metals which exist as free elements can be extracted by physical methods.
If the pieces of metal are large enough, we can pick them up by hand.
If the metal is much denser than the soil or rock mixed with it, we can wash the mixture with flowing water.
The flowing water carries the less dense particles away, leaving behind the metal.
4.2 Extracting metals from their ores (p. 67)
9Unit 4 Rocks and minerals
4.2 Extracting metals from their ores (p. 67)
A man panning for gold (淘金 )
10Unit 4 Rocks and minerals
Heating the ore alone
We can extract mercury from cinnabar (containing mercury sulphide) by heating it in air.
mercury sulphide + oxygen mercury + sulphur dioxide
4.2 Extracting metals from their ores (p. 67)
Extracting silver from silver oxide
heat in air
We can extract silver from silver oxide by heating it strongly.
silver oxide silver + oxygen
11Unit 4 Rocks and minerals
4.2 Extracting metals from their ores (p. 67)
Heating the ore with carbon We can extract iron from haematite (containing an oxide of iron) by heating it with carbon in a blast furnace.
A blast furnace (鼓風爐 )
Electrolysis of the molten ore
We can extract sodium, magnesium and aluminium by electrolyzing their molten (熔融的 ) ores.
12Unit 4 Rocks and minerals
4.2 Extracting metals from their ores (p. 67)
The availability (and hence price) of a metal depends
mainly on: - the abundance of the metal in the Earth’s crust; - the ease of mining its ore and the cost; and - the ease of extracting the metal from its ore and the cost.
13Unit 4 Rocks and minerals
4.3 Investigating calcium carbonate (p. 68)
Limestone caves are interesting geological features (地質特徵 )
Limestone is composed primarily of the mineral calcite. Calcite (方解石 ) is composed of calcium carbonate.
A limestone cave Calcite
14Unit 4 Rocks and minerals
4.3 Investigating calcium carbonate (p. 68)
Action of heat on calcium carbonate Upon heating, calcium carbonate changes to a white
powder called quicklime (calcium oxide) (生石灰 ). Carbon dioxide is also given off.
calcium carbonate calcium oxide + carbon dioxide
Heating limestone in a lime kiln, like the traditional one shown here, breaks down the calcium carbonate into calcium oxide.
heat
15Unit 4 Rocks and minerals
4.3 Investigating calcium carbonate (p. 68)
Action of heat on calcium carbonate When we add water to calcium oxide, calcium hydroxide
forms calcium oxide + water → calcium hydroxide
Calcium hydroxide is often called slaked lime (熟石灰 ). Although it is not very soluble, we can dissolve a little calcium hydroxide in water. After filtering, this produces a colourless solution called limewater (石灰水 ).
16Unit 4 Rocks and minerals
4.3 Investigating calcium carbonate (p. 68)
Action of heat on calcium carbonate Limewater is used to test for carbon dioxide gas. Carbon
dioxide turns limewater milky due to the formation of insoluble white calcium carbonate (Fig. 4.11c).
carbon + calcium calcium + water dioxide hydroxide carbonate
17Unit 4 Rocks and minerals
4.3 Investigating calcium carbonate (p. 68)
Action of heat on calcium carbonate When we pass an excess of carbon dioxide into the
limewater, the white precipitate disappears (Fig. 4.11c). This is because the precipitate dissolves to form soluble calcium hydrogencarbonate.
calcium + carbon + water → calcium carbonate dioxide hydrogencarbonate
19Unit 4 Rocks and minerals
4.3 Investigating calcium carbonate (p. 68)
Effervescence occurs when calcium carbonate reacts with dilute hydrochloric acid.
Action of dilute acid on calcium carbonate When calcium carbonate reacts with dilute hydrochloric
acid, effervescence ( 泡騰 ) occurs. Calcium chloride, water and carbon dioxide are formed.
calcium + dilute hydrochloric → calcium + water + carbon carbonate acid chloride dioxide
20Unit 4 Rocks and minerals
4.3 Investigating calcium carbonate (p. 68)
Action of water ion calcium carbonate
Calcium carbonate is insoluble in water. However, it dissolves in dilute hydrochloric acid. This is because calcium carbonate reacts with the acid to form soluble calcium chloride.
21Unit 4 Rocks and minerals
4.3 Investigating calcium carbonate (p. 68)Example
An anhydrous compound X gives a brick-red flame in a flame test. Upon strong heating, compound X gives off a gaseous product Y which turns blue cobalt(II) chloride paper pink and a gaseous product Z which turns limewater milky.
a) i) Identify gaseous products Y and Z.
ii) Write a word equation for the reaction between the gaseous product Z and limewater.
b) What can be deduced about compound X from the observation in the flame test?
c) Suggest what compound X may be?
22Unit 4 Rocks and minerals
4.3 Investigating calcium carbonate (p. 68)
Solution
a) i) Y is water vapour. Z is carbon dioxide.
ii) carbon + calcium → calcium + water dioxide hydroxide carbonate
b) Compound X contains calcium.
c) Calcium hydrogencarbonate
23Unit 4 Rocks and minerals
Practice 4.1 (p.71)The results of three tests on substances X and Y are summarized in the following table:
Test X Y
1 Flame test golden yellow flame brick-red flame
2
Addition of dilutenitric acid followed
by silver nitrate Solution to a solution
of the substance
No observable change
A white precipitate is formed
3Addition of dilute hydrochloric acid
A gas which can turn
limewater milky is evolved
No observable change
24Unit 4 Rocks and minerals
Practice 4.1 (p.71)
a) According to the results of Test 1, what species are present in X and Y respectively?
26Unit 4 Rocks and minerals
Practice 4.1 (p.71)
b) According to the results of Tests 2 and 3, explain briefly what species are present in X and Y respectively.
27Unit 4 Rocks and minerals
Practice 4.1 (p.71)
SolutionX — Carbonate ionX reacts with dilute hydrochloric acid to produce carbon dioxide gas which turns limewater milky.
Y — Chloride ionSolution of Y gives a white precipitate (silver chloride) in the silver nitrate test.
30Unit 4 Rocks and minerals
4.4 Formation of chalk, limestone and marble (p. 71)
Glass rod
The Capital in Washington DC, USA is largely constructed of marble.
Calcium carbonate occurs naturally in three main forms — chalk (白堊 ), limestone and marble (大理石 ).
Chalk is the softest among them. Limestone is harder than chalk and marble is the hardest.
31Unit 4 Rocks and minerals
4.4 Formation of chalk, limestone and marble (p. 71)
The skeletons and shells of sea animals are made up of calcium carbonate.
When these animals die, their skeletons or shells sink into the mud at the bottom of the oceans.
Over millions of years, layers build up. Pressure from the top layers changes the bottom layers into chalk.
Earth movements such as earthquakes may lift the chalk to the Earth’s surface.
Formation of limestone and limestone caves
32Unit 4 Rocks and minerals
4.4 Formation of chalk, limestone and marble (p. 71)
Earth movement may also cause the layers to sink further. Higher pressure and heat cause the chalk to turn into much
harder limestone. The limestone deposit may stay below the Earth for a long time. Higher temperature and pressure may turn the limestone into
marble.
34Unit 4 Rocks and minerals
4.5 Formation of limestone caves (p. 75)
Fireproof mat (防火墊 )
Solid rock can be broken down into smaller pieces and changed into other materials as a result of weathering (風化作用 ).
The wearing away of surface materials and the movement of products of weathering from where they formed to a different location is called erosion (侵蝕作用 ).
The major causes of erosion are gravity (重力 ), running water, waves, ice and wind.
Formations caused by wind erotion.
Stack formed by wave water
Physical and chemical weathering: http://ees.as.uky.edu/sites/default/files/elearning/module07swf.swf
35Unit 4 Rocks and minerals
4.5 Formation of limestone caves (p. 75) When rain falls, rainwater reacts with carbon dioxide in the air to
form carbonic acid (碳酸 ). water + carbon dioxide carbonic acid
When this dilute solution of carbonic acid comes into contact with underground limestone deposits, it reacts with calcium carbonate to form soluble calcium hydrogencarbonate.
calcium carbonic calcium
carbonate acid hydrogencarbonate
Underground limestone deposits are gradually dissolved in the same way over millions of years, creating underground holes called limestone caves.
+
36Unit 4 Rocks and minerals
mineral 礦物 slaked lime 熟石灰ore 礦石 limewater 石灰水extract 提取 effervescence 泡騰bauxite 鋁土礦 chalk 白堊haematite 赤鐵礦 marble 大理石cinnabar 硃砂 weathering 風化作用molten 熔融的 erosion 侵蝕作用limestone 石灰石 carbonic acid 碳酸calcite 方解石quicklime 生石灰
Key terms (p. 76)
37Unit 4 Rocks and minerals
1 The individual chemical compounds that make up rocks are called minerals. Rocks from which we obtain metals are called ores.
2 Getting a metal from its ore is called extracting the metal.
3 The following table summarizes common methods for extracting metals from their ores:
Summary (p.76)
Extraction method Example(s)Physical method panning for gold
Heating the ore alone
extracting mercury from cinnabar
extracting silver from silver oxide
Heating the ore with carbon
extracting iron from haematite
Electrolysis of the molten ore
extracting aluminium from its molten ore
38Unit 4 Rocks and minerals
4 The following table summarizes the action of heat, dilute acid and water on calcium carbonate:
Summary (p.76)
Action of Change(s)
Heat
heatcalcium carbonate → calcium oxide (quicklime) + carbon dioxidecalcium oxide + water → calcium hydroxide (slaked lime)
Dilute acid
calcium carbonate + dilute hydrochloric acid→ calcium chloride + water + carbon dioxide
Water insoluble in water but soluble in dilute hydrochloric acid
39Unit 4 Rocks and minerals
Summary (p.76)5 Limewater is a saturated solution of calcium hydroxide. It is used
to test carbon dioxide gas.
Carbon dioxide turns limewater milky due to the formation of
insoluble white calcium carbonate.
carbon dioxide + calcium hydroxide →
calcium carbonate + water
When an excess of carbon dioxide is passed into the
limewater, the white precipitate disappears. This is because
the precipitate dissolves to form soluble calcium
hydrogencarbonate. calcium carbonate + carbon dioxide + water → calcium hydrogencarbonate
40Unit 4 Rocks and minerals
Summary (p.76)
7 Solid rock can be broken down into smaller pieces and changed into other materials as a result of weathering. :
The wearing away of surface materials and the movement of products of weathering from where they formed to a different location is called erosion.
The major causes of erosion are gravity, running water, waves, ice and wind.
6 Calcium carbonate occurs naturally in three main forms — chalk, limestone and marble.