Extracting Metals by Electrolysis

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1 Extracting Metals by Electrolysis 1 of 17 Boardworks Ltd 2016

2 Extracting Metals by Electrolysis 2 of 17 Boardworks Ltd 2016

3 Methods of extracting metals 3 of 17 Boardworks Ltd 2016 Most metals are found combined with other elements, as compounds in ores. These metals must be extracted from their ores before they can be made useful. 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.

4 The reactivity series and metal extraction increasing reactivity 4 of 17 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 in their pure form (natively) and do not need to be extracted.

5 What is electrolysis? 5 of 17 Boardworks Ltd 2016 Electrolysis is a process that uses electricity to separate the elements in a compound. Electrolysis is expensive and so it is only used to extract reactive metals that cannot be extracted in other ways. Aluminium is a reactive metal that is found in the ore bauxite as aluminium oxide (Al 2 O 3 ). Electrolysis breaks down the Al 2 O 3 into aluminium and oxygen. As the aluminium loses oxygen, reduction takes place. What is the word equation for the extraction of aluminium?

Ionic substances 6 of 17 Boardworks Ltd 2016 Electrolysis involves breaking down ionic

An ionic substance contains charged particles called ions.

charge. Ions with a positive charge, such as metal ions, have lost electrons.

6 Ionic substances 6 of 17 Boardworks Ltd 2016 Electrolysis involves breaking down ionic compounds into simpler substances using electricity. An ionic substance contains charged particles called ions. An ion is an atom that has gained or lost electrons and so carries a positive or negative charge. Ions with a positive charge, such as metal ions, have lost electrons. Ions with a negative charge have gained electrons. Aluminium atom Aluminium ion In electrolysis, the ionic substance must be dissolved in water or melted so that the ions are free to move. loses 3 electrons

Oxidation and reduction 7 of 17 Boardworks Ltd

and splits up is called the electrolyte.

Negative ions move to the positive electrode and

7 Oxidation and reduction 7 of 17 Boardworks Ltd 2016 In electrolysis, electrodes are used to pass a current through a substance. The substance that the current passes through and splits up is called the electrolyte. The electrolyte contains positive and negative ions. What happens to these ions during electrolysis? Negative ions move to the positive electrode and lose electrons. This is oxidation. heat Positive ions move to the negative electrode and gain electrons. This is reduction.

OILRIG 8 of 17 Boardworks Ltd 2016 An easy way to

electrons during oxidation and reduction are

8 OILRIG 8 of 17 Boardworks Ltd 2016 An easy way to remember what happens to the electrons during oxidation and reduction is to think OILRIG. Equations written to show what happens to electrons during oxidation and reduction are called half-equations: Oxidation: Reduction: 2O 2- O 2 + 4e - Al e - Al

9 Extracting Metals by Electrolysis 9 of 17 Boardworks Ltd 2016

Extracting aluminium 10 of 17 Boardworks Ltd 2016 Electrolysis is used to extract aluminium from its ore. Why is it not possible to extract aluminium by heating its ore with carbon?

10 Extracting aluminium 10 of 17 Boardworks Ltd 2016 Electrolysis is used to extract aluminium from its ore. Why is it not possible to extract aluminium by heating its ore with carbon? Aluminium is more reactive than carbon and it s ore has a very high melting point (2050 C). This means aluminium cannot be extracted by reduction with carbon. In electrolysis, the ore is dissolved in a compound called cryolite (Na 3 AlF 6 ), which lowers the melting point to 1,000 C.

11 Extracting aluminium from bauxite 11 of 17 Boardworks Ltd 2016

At the negative electrode: Al 3+ + 3e - Al (reduction) At the positive electrode: 2O 2- O 2 + 4e -

12 Redox equations aluminium What processes occur at the electrodes during the electrolysis of aluminium oxide (Al 2 O 3 )? At the negative electrode: Al e - Al (reduction) At the positive electrode: 2O 2- O 2 + 4e - (oxidation) What is the overall equation for this extraction by electrolysis? aluminium oxide 2Al 2 O 3 (l) aluminium + oxygen 4Al (l) + 3O 2 (g) 12 of 17 Boardworks Ltd 2016

Economics of electrolysis 13 of 17 Boardworks Ltd 2016 Extracting aluminium from its ore using electrolysis requires large amounts of electrical energy. This is very expensive.

13 Economics of electrolysis 13 of 17 Boardworks Ltd 2016 Extracting aluminium from its ore using electrolysis requires large amounts of electrical energy. This is very expensive. The energy is needed to melt the aluminium oxide in the ore and to extract the aluminium by electrolysis. To reduce energy use, aluminium extraction plants are often located near sources of renewable electricity, such as hydroelectric dams.

14 Extracting aluminium summary 14 of 17 Boardworks Ltd 2016

15 Extracting Metals by Electrolysis 15 of 17 Boardworks Ltd 2016

16 Glossary 16 of 17 Boardworks Ltd 2016

17 Multiple-choice quiz 17 of 17 Boardworks Ltd 2016

Extracting Metals by Reduction

Extracting Metals by Reduction 1 of 19 Boardworks Ltd 2016 Extracting Metals by Reduction 2 of 19 Boardworks Ltd 2016 Finding metals 3 of 19 Boardworks Ltd 2016 Where are metals found? Are some easier