1A 2nd The Planet Earth Unit 4 Rocks and Minerals (Eng).pptx

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


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.



A stainless steel sink



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)


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:


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.




A man panning for gold (淘金 )


Heating the ore alone

We can extract mercury from cinnabar (containing mercury sulphide) by heating it in air.

mercury sulphide + oxygen mercury + sulphur dioxide


Extracting silver from silver oxide

heat in air

We can extract silver from silver oxide by heating it strongly.

silver oxide silver + oxygen



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.



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.


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



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



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 ).



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



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





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



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.


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?



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


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


Practice 4.1 (p.71)

a) According to the results of Test 1, what species are present in X and Y respectively?


Practice 4.1 (p.71)

SolutionX — Sodium

Y — Calcium


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.


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.


Practice 4.1 (p.71)

c) Name X and Y.


Practice 4.1 (p.71)

Solution

X — Sodium carbonate

Y — Calcium chloride


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.



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



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.



Uses of limestone.


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

http://ees.as.uky.edu/sites/default/files/elearning/module07swf.swf

http://ees.as.uky.edu/sites/default/files/elearning/module07swf.swf


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.

+


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)


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


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


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


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.

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1A 2nd The Planet Earth Unit 4 Rocks and Minerals (Eng).pptx