Extracting Metals by Reduction

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1 Extracting Metals by Reduction 1 of 19 Boardworks Ltd 2016

2 Extracting Metals by Reduction 2 of 19 Boardworks Ltd 2016

3 Finding metals 3 of 19 Boardworks Ltd 2016 Where are metals found? Are some easier to find than others?

4 Where do metals come from? 4 of 19 Boardworks Ltd 2016 Some unreactive metals, like gold, silver and copper, are found in the Earth s crust as pure substances. Native metals are metals found in a pure form. Most metals are actually found combined with other elements, as compounds in ores. These metals must be extracted from their ores before they can be made useful. Highly reactive metals, such as titanium, require complicated extraction which can increase the cost of the pure metal.

5 Methods of extracting metals 5 of 19 Boardworks Ltd 2016 There are two main methods of extracting metals from their ores: reduction with carbon electrolysis (using electricity). The method of extraction which is most appropriate depends on the reactivity of the metal being extracted. The reactivity series of metals can be determined by comparing the reactivity of metals with other compounds, such as acids, or by carrying out displacement reactions.

6 Reacting metals with acid 6 of 19 Boardworks Ltd 2016

7 Displacement reactions 7 of 19 Boardworks Ltd 2016

8 The reactivity series and metal extraction increasing reactivity 8 of 19 Boardworks Ltd 2016 The reactivity of a metal determines how it is extracted. potassium sodium calcium magnesium aluminium (carbon) zinc iron lead (hydrogen) copper silver gold platinum Metals above carbon in the reactivity series must be extracted using electrolysis. Metals less reactive than carbon can be extracted from their ores by reduction. Copper, silver, gold and platinum can occur as native metals and do not need to be extracted. Sometimes copper needs to be extracted from an ore.

9 Metal extraction activity 9 of 19 Boardworks Ltd 2016

10 Extracting Metals by Reduction 10 of 19 Boardworks Ltd 2016

11 Reduction of metal oxides 11 of 19 Boardworks Ltd 2016 Metals are often found combined with oxygen as oxides. To obtain the metal, the oxygen must be removed. During reduction, oxygen can be removed from a substance or electrons are gained by a substance. During oxidation, oxygen can be added to a substance, or electrons are removed from a substance. Reduction of the metal oxide is used to extract the metal:

12 Extracting metals using carbon 12 of 19 Boardworks Ltd 2016 Carbon can be used to extract some metals from their metal oxides by reduction. For example, the extraction of lead from lead oxide: This is a displacement reaction, and occurs because carbon is more reactive than lead. In this reaction, the lead oxide is reduced in this reaction while carbon is oxidised.

13 Metal oxides and carbon 13 of 19 Boardworks Ltd 2016

14 Extraction of zinc by reduction 14 of 19 Boardworks Ltd 2016 Zinc oxide, ZnO, reacts with carbon at very high temperatures to form molten zinc and carbon monoxide. This is also a displacement reaction, and occurs because carbon is more reactive than zinc. ZnO(s) + C(s) reduction Zn(l) + CO(g) The more reactive carbon displaces the zinc atom, causing the zinc oxygen bond to break while a new carbon-oxygen bond forms. In this reaction, what is oxidised and what is reduced?

15 Reducing metals with carbon activity 15 of 19 Boardworks Ltd 2016

16 Comparing extraction methods 16 of 19 Boardworks Ltd 2016 The majority of the world s zinc is obtained by electrolysis of zinc sulfate, while only 15% is obtained by reduction with carbon. The table below compares extraction of metals by reduction and electrolysis: electrolysis reduction temperature C 1000 C purity of zinc 99.99% >95% greenhouse gas production SO 2 SO 2 and CO Which method would you choose?

17 Extracting Metals by Reduction 17 of 19 Boardworks Ltd 2016

18 Glossary 18 of 19 Boardworks Ltd 2016

19 Multiple-choice quiz 19 of 19 Boardworks Ltd 2016