Chapter 4. Rocks and minerals

Transcription

1 Chapter 4 Rocks and minerals 4.1 Rocks as a source of minerals 4.2 Extraction of metals from their ores 4.3 Limestone, chalk and marble 4.4 Weathering and erosion of rocks 4.5 Chemical changes involving calcium carbonate 4.6 Tests for the presence of calcium and carbonate in a sample of limestone/chalk/marble Key terms Progress check Summary Concept map P. 1 / 52

2 4.1 Rocks as a source of minerals What are rocks and minerals? A rock is a solid mass of mineral or a mixture of minerals. Minerals may be elements, like gold and carbon (in diamond), which are found free in rocks. More commonly, they are compounds. P. 2 / 52

3 Learning tip Silicon and oxygen are the two abundant elements that form the major types of minerals in the Earth s crust. The rock marble contains mostly the mineral calcite. The chemical composition of calcite is calcium carbonate. Figure 4.1 Calcite 4.1 Rocks as a source of minerals P. 3 / 52

4 The rock granite is a mixture of minerals: quartz, feldspar and mica. Quartz is a compound made up of silicon and oxygen. Mica and feldspar are two different types of compounds, which are made up of silicon, oxygen and other elements. Figure 4.2 Granite 4.1 Rocks as a source of minerals P. 4 / 52

5 Minerals and ores An ore is the type of rocks that contains minerals, from which a high proportion of useful elements (usually contains metal) can be extracted. Most of the metals used in daily life are extracted from their ores. 4.1 Rocks as a source of minerals P. 5 / 52

6 (a) Bauxite the main ore of aluminium. It is mostly aluminium oxide. (b) Copper pyrite the main ore of copper. It is mostly copper iron sulphide. (c) Haematite the main ore of iron. It is mostly iron(iii) oxide. (d) Galena the main ore of lead. It is mostly lead(ii) sulphide. Figure 4.3 Some examples of common ores. 4.1 Rocks as a source of minerals P. 6 / 52

7 4.2 Extraction of metals from their ores Metals can be extracted from their ores by physical methods or chemical methods. Physical change Key point A physical change is a change in which no new substances are produced. P. 7 / 52

8 sublimation ice solid deposition gas liquid water Figure 4.4 Melting of ice is a physical change. liquid heat absorbed heat given out Figure 4.5 Change of state is a common example of physical change. 4.2 Extraction of metals from their ores P. 8 / 52

9 evaporating dish water iodine solid iodine solid iodine vapour Bunsen flame Figure 4.6 Iodine solid sublimes to form vapour on heating. When in contact with a cool surface, the iodine vapour changes back directly to iodine solid, without passing through the liquid state. 4.2 Extraction of metals from their ores P. 9 / 52

10 Chemical change Key point A chemical change is a change in which one or more new substances are produced. Figure 4.7 Burning a piece of paper is a chemical change. 4.2 Extraction of metals from their ores P. 10 / 52

11 The reaction between copper and chlorine is another example of chemical change. The elements copper and chlorine are chemically combined to form a compound called copper(ii) chloride. Word equation: reacts with to produce copper + chlorine copper(ii) chloride reactants product 4.2 Extraction of metals from their ores P. 11 / 52

12 combustion spoon brown copper(ii) chloride copper powder chlorine (a) (b) Figure 4.8 The reaction between copper and chlorine is a chemical change. (a) Heating copper powder to red hot (b) Reaction of hot copper with chlorine to form brown copper(ii) chloride. 4.2 Extraction of metals from their ores P. 12 / 52

13 Physical methods used to extract metals from their ores A few unreactive metals (e.g. gold and platinum) exist as free elements in the Earth s crust. They can be extracted by mechanical separation, e.g. panning. Figure 4.9 Gold panning. 4.2 Extraction of metals from their ores P. 13 / 52

14 Chemical methods used to extract metals from their ores Heating the metal ore alone Some unreactive metals, such as mercury and silver, are extracted by heating their ores in air. Example Silver can be extracted from silver oxide (found in some silver ores) by heating it strongly in air. heat silver oxide silver + oxygen 4.2 Extraction of metals from their ores P. 14 / 52

15 Heating the metal ore with carbon Some metals, such as zinc, iron and lead, are extracted by heating their ores with carbon. Example Lead can be extracted from lead(ii) oxide (found in some lead ores) by heating it with carbon strongly. heat lead(ii) oxide + carbon lead + carbon dioxide 4.2 Extraction of metals from their ores P. 15 / 52

16 Electrolysis of molten ore Some metals, such as sodium, magnesium and aluminium, are extracted by electrolysis of their molten ores. Example Aluminium is extracted from aluminium oxide by passing electricity through it. aluminium oxide electrolysis aluminium + oxygen STSE connections 4.1 Class practice 4.1 Activity Extraction of metals from their ores P. 16 / 52

17 4.3 Limestone, chalk and marble Rocks containing calcium carbonate Limestone, chalk and marble are common rocks which contain the mineral calcite. Its chemical composition is calcium carbonate. Limestone cave in Carlsbad, New Mexico. Figure 4.10 Limestone cave, chalk curves and marble cave. P. 17 / 52

18 Chalk cliffs in Sussex, England. Marble canyon in Taroko Gorge, Taiwan. Figure 4.10 Limestone cave, chalk curves and marble cave. In other words, limestone, chalk and marble are three different rocks that contain naturally occurring calcium carbonate. 4.3 Limestone, chalk and marble P. 18 / 52

19 Uses of limestone As the construction material for some footpaths To make glass Powdered limestone to neutralize acidic soil To make cement Limestone Figure 4.11 Some common uses of limestone To build statue 4.3 Limestone, chalk and marble P. 19 / 52

20 4.4 Weathering and erosion of rocks Weathering of rocks occurs due to changes in atmospheric conditions, such as temperature change, and also actions of water and chemicals in the environment (e.g. carbonic acid in rainwater). Weathering of rocks is a slow process. This process is called erosion. P. 20 / 52

21 Weathering by temperature changes Changes in temperature can break the rocks. Figure 4.12 Rocks in deserts get hot in the daytime and cool down quickly at night. They are badly weathered. 4.4 Weathering and erosion of rocks P. 21 / 52

22 Weathering by frost action rainwater gathers in a crack ice eventually a piece of rock breaks off water freezes and expands rock the crack gets bigger temperature falls below 0 C (a) (b) (c) Figure 4.13 Expanding ice breaks rocks. 4.4 Weathering and erosion of rocks P. 22 / 52

23 Weathering by acidic substances Rainwater is slightly acidic because carbon dioxide in air dissolves slightly in it, forming carbonic acid. carbon dioxide + water carbonic acid The carbonic acid formed reacts with calcium carbonate in rocks such as chalk and limestone. calcium carbonate + carbonic acid calcium hydrogencarbonate acidic 4.4 Weathering and erosion of rocks P. 23 / 52

24 Figure 4.14 A sinkhole in limestone area. Figure 4.15 This limestone statue has been weathered by rainwater. 4.4 Weathering and erosion of rocks P. 24 / 52

25 4.5 Chemical changes involving calcium carbonate Thermal decomposition of calcium carbonate Calcium carbonate decomposes to calcium oxide and carbon dioxide when it is heated strongly. heat calcium carbonate calcium oxide + carbon dioxide white solid The calcium oxide formed is commonly known as quicklime. P. 25 / 52

26 When water is added to calcium oxide, calcium hydroxide (slaked lime) forms and a lot of heat is produced. calcium oxide + water calcium hydroxide (quicklime) (slaked lime) Calcium hydroxide is only slightly soluble in water. When water is added to calcium hydroxide, a saturated solution with white suspension forms. 4.5 Chemical changes involving calcium carbonate P. 26 / 52

27 After suspension is filtered, a colourless solution is obtained. The filtrate obtained is called limewater. Figure 4.16 Suspension of calcium hydroxide in water Figure 4.17 Limewater 4.5 Chemical changes involving calcium carbonate P. 27 / 52

28 Test for carbon dioxide Limewater turns milky when carbon dioxide is passed into it for a few seconds. Carbon dioxide reacts with calcium hydroxide solution to give a white insoluble solid which is calcium carbonate. calcium hydroxide + carbon dioxide colourless solution calcium carbonate + water white solid Key point Carbon dioxide is a colourless gas. It turns limewater. milky 4.5 Chemical changes involving calcium carbonate P. 28 / 52

29 delivery tube carbon dioxide calcium carbonate limewater heat delivery tube calcium carbonate limewater Figure 4.18 Test for carbon dioxide using limewater. 4.5 Chemical changes involving calcium carbonate P. 29 / 52

30 If excess carbon dioxide is continuously passed into the limewater, the milky solution will become colourless. Because the insoluble calcium carbonate reacts with the excess carbon dioxide and water to form soluble calcium hydrogencarbonate. calcium carbonate + carbon dioxide + water white solid calcium hydrogencarbonate colourless solution 4.5 Chemical changes involving calcium carbonate P. 30 / 52

31 pass carbon dioxide into it pass excess carbon dioxide into it limewater limewater turns milky milky limewater becomes colourless (a) (b) Figure 4.19 (a) Limewater (b) The limewater turns milky when carbon dioxide is passed into it. (c) The milky limewater becomes colourless when excess carbon dioxide is passed into it. 4.5 Chemical changes involving calcium carbonate Example 4.1 P. 31 / 52 (c)

32 4. pass carbon dioxide into it (limewater test) calcium carbonate 1. strong heat carbon dioxide given off calcium hydroxide solution (limewater) calcium oxide (quicklime) 3. add more water, stir well and then filter calcium hydroxide (slaked lime) 2. add a little water Figure 4.20 Some chemical changes involving calcium carbonate. Class practice 4.2 Experiment 4.1 Experiment Chemical changes involving calcium carbonate P. 32 / 52

33 4.6 Tests for the presence of calcium and carbonate in a sample of limestone/ chalk/marble Test for the presence of calcium Calcium compounds give a brick-red flame in the flame test. Figure 4.21 Calcium compounds give a brick-red flame in the flame test. P. 33 / 52

34 Test for the presence of carbonate Dilute hydrochloric acid is added to a sample. If carbonate is present, carbon dioxide is produced, which turns limewater milky. delivery tube dilute hydrochloric acid solid sample under test limewater Figure 4.22 Test for the presence of carbonate using limewater test. 4.6 Tests for the presence of calcium and carbonate in a sample of limestone/chalk/marble P. 34 / 52

35 Limestone, chalk and marble all give a brick-red flame in the flame test and positive results in the limewater test. Experiment 4.2 Experiment 4.2 Class practice Tests for the presence of calcium and carbonate in a sample of limestone/chalk/marble P. 35 / 52

36 Key terms 1. calcite 方解石 2. calcium carbonate 碳酸鈣 3. chalk 白堊 4. chemical change 化學變化 5. erosion 侵蝕作用 6. limestone 石灰石 7. limewater 石灰水 8. marble 大理石 9. mineral 礦物 P. 36 / 52

37 10. ore 礦石 11. physical change 物理變化 12. rock 岩石 13. quicklime 生石灰 14. slaked lime 熟石灰 15. sublimation 昇華 16. weathering 風化作用 17. word equation 文字方程式 Key terms P. 37 / 52

38 Progress check 1. What is a rock? 2. What is a mineral? 3. What is an ore? 4. What is a physical change? 5. What is a chemical change? 6. What are the common methods for extraction of metals from their ores? 7. What is the common mineral present in limestone, chalk and marble? P. 38 / 52

39 8. What is weathering? 9. What is erosion? 10.What are the effects of the action of heat on calcium carbonate? 11.What are the effects of the action of water on calcium carbonate? 12.What are the effects of the action of acids on calcium carbonate? 13.What is the relationship between limestone, quicklime, slaked lime and limewater? Progress check P. 39 / 52

40 14.How can we test for the presence of calcium in limestone/chalk/marble? 15.How can we test for the presence of carbonate in limestone/chalk/marble? Progress check P. 40 / 52

41 Summary 4.1 Rocks as a source of minerals 1. A rock is a solid mass of a mineral or a mixture of minerals. 2. A mineral is a naturally occurring chemical that makes up the rocks. 3. An ore is the type of rock that contains minerals, from which a high proportion of useful elements (usually contains metal) can be extracted. Some common ores include bauxite, copper pyrite and haematite. P. 41 / 52

42 4.2 Extraction of metals from their ores 4. A physical change is a change in which no new substances are produced. Example: change of states of a substance 5. A chemical change is a change in which one or more new substances are produced. Example: burning a piece of paper Summary P. 42 / 52

43 6. Metals can be extracted from their ores by the following methods: Physical methods Heating the metal ore alone Heating the metal ore with carbon Electrolysis of the molten ore 4.3 Limestone, chalk and marble 7. Limestone, chalk and marble are common rocks that contain naturally occurring calcium carbonate. 8. Limestone is a very useful rock. Refer to p.9 for some of its uses. Summary P. 43 / 52

44 4.4 Weathering and erosion of rocks 9. Weathering of rocks is a slow process (usually taking place over thousands of years) in which exposed rocks are broken down into smaller pieces or changed into other substances. 10. Erosion of rocks refers to a slow process in which weathered rock pieces are transported away by gravity, wind and water. 11. Rocks are weathered by temperature changes frost action acidic substances, e.g. acidic rainwater Summary P. 44 / 52

45 4.5 Chemical changes involving calcium carbonate 12. On strong heating, calcium carbonate decomposes to calcium oxide (quicklime) and carbon dioxide. heat calcium carbonate calcium oxide + carbon dioxide (quicklime) 13. When calcium oxide (quicklime) is treated with water, it changes to calcium hydroxide (slaked lime). calcium oxide + water calcium hydroxide (slaked lime) Summary P. 45 / 52

46 14. Limewater is a saturated solution of calcium hydroxide. It is a colourless solution, which turns milky when carbon dioxide is passed into it for a few seconds. It can be used to test for the presence of carbon dioxide. calcium hydroxide + carbon dioxide colourless solution calcium carbonate + water white solid Summary P. 46 / 52

47 15. If excess carbon dioxide is passed into limewater, the milky solution will become colourless because the insoluble calcium carbonate reacts with the excess carbon dioxide and water to form soluble calcium hydrogencarbonate. calcium carbonate + carbon dioxide + water white solid calcium hydrogencarbonate colourless solution Summary P. 47 / 52

48 16. Calcium carbonate reacts with dilute hydrochloric acid to give carbon dioxide. calcium carbonate + dilute hydrochloric acid calcium chloride + water + carbon dioxide 4.6 Tests for the presence of calcium and carbonate in a sample of limestone/ chalk/marble 17. Calcium compounds give a brick-red flame in the flame test. 18. Calcium carbonate gives off carbon dioxide when it reacts with dilute hydrochloric acid. Summary P. 48 / 52

49 Concept map MINERALS Ores contain a high proportion of useful elements methods of extracting metals from their ores Physical methods Heating the metal ore alone Heating the metal ore with carbon Electrolysis of the molten ore P. 49 / 52

50 Erosion the process of transporting rocks pieces away by gravity, wind and water Weathering the process of breaking down rocks into smaller pieces Rocks contains MINERALS Concept map P. 50 / 52

51 Rocks calcite containing Limestone Chalk Marble Calcium carbonate strong heating add carbon dioxide Calcium oxide ( ) Quicklime add water Calcium hydroxide ( ) Slaked lime Concept map P. 51 / 52

52 flame test Brick-red flame which shows that it contains Calcium Calcium carbonate add dilute hydrochloric acid Carbon dioxide evolved which shows that it contains Carbonate Concept map P. 52 / 52