1	Core & Extension Metals III: Extraction
2	Learning objectives Concepts ore, native, extraction, bauxite, hematite, zinc blende, blast furnace, gangue, smelting, electrolysis, oxidization, oxidized, reduction, reduced, thermal decomposition, galvanization Skills Core: Describe and relate position of metals in the reactivity series to the ease of obtaining the metals from their ore Describe essential reactions in the extraction of iron from hematite name the uses of calcium carbonate in the manufacture of iron and of cement describe the manufacture of lime (calcium oxide) from calcium carbonate (limestone) in terms of the chemical reactions involved.
3	Learning objectives Extension: Describe in outline, the extraction of zinc from zinc blende
4	Human discovery of metals Approximate dates Copper for weapons & jewellery
5	Human discovery of metals Approximate dates aluminium (zinc, lead etc.)
6	Reactivity, discovery & use 1. Why were gold and silver the first discovered and used metals? 2. Gold, silver and some copper are naturally occurring because …….. 3. How do we produce the other metals that are not naturally occurring? 4. What is the starting material and where do we get it from?
7	Metal Ores Most metals are reactive enough to not exist in their free state in the Earth’s crust and are found in compounds called ORES. The more reactive a metal is, the more likely it will be found in an ore. They either occur as their oxide or sulfide. Some common ores you need to know are... Bauxite (Al₂O₃) is an ore of aluminium. Haematite (Fe₂O₃) is an ore of iron. Zinc blende (ZnS) is an ore of zinc.
8	Ore formation
9	Native Metals Unreactive metals do not react with other elements in the earths surface. They can be found in their natural or native state The less reactive a metal is, the more likely it will be found in native form. Some metals that are found native are...
10	Native Metals These metals are all at the bottom end of the reactivity series. Gold and platinum (sometimes silver) as they are found native, they do not need to be extracted from their ore. That is why gold and silver were one of the first metals to be discovered. The higher up in the reactivity series a metal is, the harder it is to extract that metal from its ore.
11	Metal Extraction
12	Exercise 1: Link the Ores and Metals
13	Exercise 2: Link the Boxes
14	Exercise 3: Finding Metals
15	Extraction of metals Once the ores have been mined from the ground, they are crushed. Then the metal must be extracted from the ore. As has already been mentioned, we will restrict our studies of extraction to extraction by reduction by carbon and electrolysis. The next question is which metals can be extracted by reduction by carbon and which by electrolysis? Those metals that are relatively unreactive, those are less reactive than carbon are extracted by reduction by carbon, while those that are more reactive by electrolysis.
16	Carbon Position in the Reactivity Series C Al₂O₃
17	Reduction by Carbon
18	Extracting Metals from their Ores The metals that are less reactive than carbon in the reactivity series such as lead, tin and iron can have their oxides heated in the presence of carbon. The oxides then undergo reduction and you are left with the metal. The extraction of iron and zinc from its ore using carbon is a very important industrial process that you will need to study carefully, you will also need to know the important implications it has on the environment.
19	Extraction by Reduction: Iron Ferrum is the latin word for iron, hence the chemical symbol “Fe.” It is the fourth most abundant element on the surface of the earth. It is however the next most abundant metal (after alumunum). It has however been used for thousands of years and is the most important metal (followed by aluminum). It is magnetic, malleable and silvery white metallic element. Iron is very hard. Trace amount of the metal occur in combination is natural water, plants, and as a constituent of haemoglobin in blood.
20	The Importance of Iron
21	Exercise 1: The Blast Furnace
22	Blast Furnace Reactions
23	Overview of Blast Furnace Reactions
24	Exercise 2: The Conditions in the Blast Furnace
25	Exercise 3: Direct Reduction
26	Exercise 4: Limestone
27	Cement from Limestone Limestone, a form of calcium carbonate (others being chalk and marble), also finds use in cement manufacture and lime production (in addition to being used in the extraction of iron) Cement manufacture first involves heating powdered limestone with clay in kiln. The product is then powdered and mixed with gypsum (CaSO₄•2H₂O). The result is a mixture to which when water is added a complex chemical reaction produces the hard solid cement consisting of calcium aluminate (Ca(AlO₂)₂) and calcium silicate (CaSiO₃).
28	Lime from Limestone Lime or quicklime (CaO) production essentially involves the thermal decomposition reaction that limestone undergoes in the blast furnace. The limestone is roasted in a lime kiln with an open top. CaCO_3(s) ® CaO_(s) + CO_2(g)
29	Extension: Extraction of Zinc Since zinc is also less reactive than carbon, zinc is also extracted using a similar method to iron. The main ore of zinc is zinc blende (zinc sulfide). The first step in its extraction after the ore is mined is concentration (or purification), separation of the ore from the gangue, impurities. Crushed ore is fed into tanks of water containing an oil-detergent mixture and air blown through the mixture while being stirred. Heavier contaminants sink to the bottom, while the oil coated lighter mineral particles rise to the surface of the oily froth. The oily mineral particles are then skimmed off with the froth, cleaned and dried.
30	Extension: Extraction of Zinc The next step is the actual process of extraction from the clean and dry mineral particles. The enriched sulfide ore is first converted into the oxide by roasting it in air. 2ZnS _(s) + O_{2 (g)} à ZnO_(s) + SO_{2 (g)} Then what follows is very similar to the processes carried out in the extraction of iron from hematite. The oxide is heated in a blast furnace with coke. Carbon monoxide reduces zinc oxide to zinc. 2ZnO _(s) + CO_(g) à Zn _(g) + CO_{2 (g)} Notice that zinc vapor is produced instead of molten zinc because the temperature (of over 1000°C) in the furnace is higher than the boiling point (992°C) of zinc.
31	Extraction of Aluminum The vapor passes out of the furnace and is cooled and condensed. See Electrochemistry for details of extraction of Aluminum, Sodium and Chlorine.
32	Summary Those metals below carbon in the reactivity series are extracted by reduction by carbon. Reactive metals, metals that are more reactive than carbon are extracted by electrolysis as carbon would not be able to displace the metals from its oxide ore. Two metals extracted by reduction are iron and zinc. The reduction is carried out in a blast furnace. The raw materials are the ore (hematite in the case of iron, and zinc blende in the case of zinc), coke and limestone. Limestone removes impurities. Another use of limestone is in the production of lime (CaO) and slaked lime (Ca(OH)₂).
33	Paper 2 Practice Questions 1. J04/2/6. Iron is extracted from its ore in a blast furnace using carbon (coke) as a reducing agent and as a source of heat. (a) The coke burns in hot air. The equation for this reaction is 2C(s) + O₂(g) ® 2CO(g) State the name of the gas produced in this reaction. [1] (b) Near the top of the blast furnace, the iron(III) oxide in the iron ore gets reduced to iron. Fe₂O₃(s) + 3CO(g) ® 2Fe(l) + 3CO₂(g) Use the equation to explain why the change of iron(III) oxide to iron is a reduction reaction. [1]
34	Paper 2 Practice Questions (c) In the hottest regions of the furnace, iron(III) oxide is reduced by carbon. Complete the equation for this reaction. Fe₂O₃(s) + …… C(s) ® ……Fe(l) + 3CO(g) [2]
35	Paper 2 Practice Questions (a) State one use of limestone, other than in making lime. [1] (b) Coke is mainly carbon. Write a symbol equation for the burning of carbon. [2] (c) State the name of the type of reaction which releases heat energy. [1] (d) The heat produced by the burning coke causes thermal decomposition of the limestone. Complete the word equation for the thermal decomposition of calcium carbonate. calcium carbonate → [2]
36	Paper 2 Practice Questions (e) (i) Complete the following equation for the reaction of calcium carbonate with hydrochloric acid. CaCO₃ + … HCl → CaCl₂ + CO₂ + H₂O (ii) Describe how you would test for the gas given off in this reaction. test result [3]
37	Paper 2 Practice Questions 3. N02/2/5. Iron is extracted from the ore, haematite. The iron ore is put in a blast furnace with coke and a current of air is blown through the heated mixture. (a) What do you understand by the term ore? [1]
38	Paper 2 Practice Questions (b) What other raw material needs to be added to the blast furnace? Put a ring around the correct answer. cement limewater limestone slag [1] (c) Near the bottom of the furnace, iron(III) oxide is reduced by carbon. Fe₂O₃ + 3C ® 2Fe + 3CO (i) Write a word equation for this reaction. [1] (ii) Explain what is meant by the term reduction. [1] (d) The table (on the next slide) shows the composition of the waste gases leaving the blast furnace.
39	Paper 2 Practice Questions
40	Paper 3 Practice Questions 1. J03/3/6. The list below shows part of the metal reactivity series . potassium more reactive magnesium aluminium zinc iron copper less reactive (a) From this list, choose a metal which is extracted using electrolysis. [1] (b) Two thousand years ago, people were able to extract iron and copper from their ores. They were not able to extract aluminium. Suggest why they were not able to extract aluminium from its ore. [1]
41	Paper 3 Practice Questions 2. J03/3/6 (f) Zinc can be extracted by heating zinc oxide with carbon. ZnO + C → Zn + CO Explain why carbon is a reducing agent (reductant) in this reaction. [1] 3. N03/3/3. Zinc blende is the common ore of zinc. It is usually found mixed with an ore of lead and traces of silver. (a) (i) Describe how zinc blende is changed into zinc oxide. [2]
42	Paper 3 Practice Questions (ii) Write an equation for the reduction of zinc oxide by carbon. [2] (iii) The boiling point of lead is 1740 °C and that of zinc is 907 °C. Explain why, when both oxides are reduced by heating with carbon at 1400 °C, only lead remains in the furnace. [2] 4. J03/3/1. No one knows where iron was first isolated. It appeared in China, the Middle East and in Africa. It was obtained by reducing iron ore with charcoal.
43	Paper 3 Practice Questions (a) Complete the following equation. Fe₂O₃ + C → ................... + ........................ [2]
44	Paper 3 Practice Questions (i) The temperature in the furnace rises to 2000 °C. Write an equation for the exothermic reaction that causes this high temperature. (ii) In the furnace, the ore is reduced by carbon monoxide. Explain how this is formed. [3] (c) The formation of slag removes an impurity in the ore. Write a word equation for the formation of the slag. [2]
45	Paper 3 Practice Questions N01/3/4. (a) Zinc is made by reducing zinc oxide. In 1695 Homberg obtained zinc from calamine, zinc carbonate. At present zinc is extracted from the ore, zinc blende. (ii) Describe how zinc is extracted from zinc blende. [3]