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Extracting Metals by Electrolysis

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1 Extracting Metals by Electrolysis
Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis Extracting Metals by Electrolysis

2 Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis

3 Extracting metals from ores
Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis Most metals that we use are found combined with other elements, as compounds in ores. These metals must be extracted from their ores before they can be made useful. potassium The method of extraction which is most appropriate depends on the reactivity of the metal being extracted. This can be discovered using the reactivity series. increasing reactivity sodium calcium magnesium aluminium (carbon) zinc iron Teacher notes See the Extracting Metals by Reduction presentation for more information on ores and extracting metals by reduction. This content is higher tier for Edexcel GCSE Science. lead (hydrogen) Metals above carbon in the reactivity series must be extracted using electrolysis. copper silver gold platinum

4 Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis
What is electrolysis? Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis 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 combined with oxygen as aluminium oxide (Al2O3). Electrolysis breaks down the Al2O3 into aluminium and oxygen. As the aluminium loses oxygen, reduction takes place. Photo credit: © Dave Dyet. This image is in the public domain. What is the word equation for the extraction of aluminium? aluminium oxide aluminium oxygen +

5 Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis
Ionic substances Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis Electrolysis involves breaking down ionic substances 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, which is shown after its formula. Al Aluminium atom loses 3 electrons Al3+ Aluminium ion Ions with a positive charge have lost electrons, and ions with a negative charge have gained electrons. Teacher notes An ion is an atom or group of atoms that has an electrical charge, either positive or negative. Atoms have an equal number of protons and electrons and so do not have an overall charge. Atoms with incomplete outer electron shells are unstable. By either gaining or losing electrons, atoms can obtain full outer electron shells and become stable. When this happens, atoms have an unequal number of protons and electrons and so have an overall charge. This is how atoms become ions. An atom that loses electrons has more protons than electrons and so has a positive overall charge. This is called a positive ion. Metal atoms, such as sodium, magnesium and iron, form positive ions. An atom that gains electrons has more electrons than protons and so has a negative overall charge. This is called a negative ion. Non-metal atoms, such as chlorine, oxygen and nitrogen, form negative ions. The electron configuration of an atom shows how many electrons it must lose or gain to have a filled outer shell. Atoms with a nearly empty outer shell will lose electrons to obtain a full outer shell. Atoms with a nearly full outer shell will gain electrons to obtain a full outer shell. In electrolysis, the ionic substance must be dissolved in water or melted so that the ions are free to move.

6 Oxidation and reduction
Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis In electrolysis, 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? heat This content is higher tier for OCR Gateway GCSE Science. Negative ions move to the positive electrode and lose electrons. This is oxidation. Positive ions move to the negative electrode and gain electrons. This is reduction.

7 Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis
OILRIG Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis An easy way to remember what happens to the electrons during oxidation and reduction is to think OILRIG. Oxidation Is Loss of electrons Reduction Is Gain of electrons Equations written to show what happens to electrons during oxidation and reduction are called half-equations, i.e.: magnesium + oxygen magnesium oxide 2Mg (s) O2 (g) 2MgO (s) + This content is higher tier for OCR Gateway GCSE Science. oxidation: Mg Mg e- reduction: O2 + 4e O2-

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Extracting aluminium Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis Aluminium is one of the most useful metals in the world. Electrolysis is used to extract aluminium from its ore. Why is it not possible to extract aluminium by heating its ore with carbon? Aluminium ore (bauxite) is more reactive than carbon and has a very high melting point (2050 °C). Teacher notes It is not possible to extract aluminium by heating its ore with carbon because aluminium is more reactive than carbon, as can be seen in the reactivity series. The melting point of aluminium oxide is very high, making heating it with carbon not viable. Photo credit: © Gemenacom, 2011 Shutterstock.com In electrolysis, the ore is dissolved in a compound called cryolite (Na3AlF6), which effectively lowers the melting point to 1,000 °C.

9 Aluminium from bauxite
Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis Teacher notes This virtual experiment illustrates how aluminium can be extracted from its ore using electrolysis. Students may need to be reminded of how ions are formed before viewing this animation.

10 Redox equations – aluminium
Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis What processes occur at the electrodes during the electrolysis of aluminium oxide (Al2O3)? At the negative electrode: Al3+ + 3e- Al (reduction) At the positive electrode: 2O O2 + 4e- (oxidation) Teacher notes This reaction may be known as a ‘redox’ reaction as both reduction and oxidation are taking place. What is the overall equation for this extraction by electrolysis? aluminium oxide aluminium + oxygen 2 Al2O3 (l) Al (l) + 3 O2 (g)

11 Economics of electrolysis
Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis The extraction of aluminium from its ore by electrolysis requires large amounts of energy in the form of expensive electricity to complete the many stages in the process. This energy is needed both to melt the aluminium oxide and to split up the compound. To reduce costs, aluminium extraction plants are often located near sources of cheap electricity such as hydroelectric dams. Photo credit: © liza1979, 2011 Shutterstock.com

12 Extracting aluminium summary
Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis Teacher notes This completing sentences activity provides the opportunity for some informal assessment of students’ understanding of how aluminium is extracted. This slide is accompanied by the worksheet Extracting Metals by Electrolysis.

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14 Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis
How is copper purified? Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis Copper is an excellent conductor and does not corrode quickly which makes it a good material for wiring and plumbing Only pure copper can be used for electric wires because even very low levels of impurities will reduce the conductivity. Copper can occur as a native metal, but more often it is found combined with other elements, such as in the ore malachite. Photo credit: © polat, 2011 Shutterstock.com The copper extracted from compounds by reduction with carbon is impure. Electrolysis can be used after reduction to remove the impurities and obtain pure copper.

15 Purifying copper using electrolysis
Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis Teacher notes This virtual experiment illustrates how copper can be purified by electrolysis. It could be used as a precursor to running the practical in the lab, or as a revision exercise. This content is higher tier for OCR Gateway GCSE Science.

16 Labelling copper purification
Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis Teacher notes This drag and drop activity could be used as a plenary exercise to check students’ ability to label the parts and reactants in copper electrolysis. Class voting or the use of coloured traffic light cards could make this a whole-class exercise. Alternatively, students could be asked to complete the diagram in their books and the activity could be concluded by the completion on the IWB. This content is higher tier for OCR Gateway GCSE Science.

17 Redox equations – copper
Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis What happens at the electrodes during the purification of copper by electrolysis? At the negative electrode: Cu2+ + 2e- Cu (reduction) At the positive electrode: Cu Cu2+ + 2e- (oxidation) This process is carried out on a huge scale in industry The copper formed on the negative electrodes is 99.99% pure. The precious metals recovered from the impurities are also sold off and help to make this industrial process profitable.

18 Purifying copper – true or false?
Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis Teacher notes This true-or-false activity could be used as a plenary or revision exercise on purifying copper, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.

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20 Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis
Glossary Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis Teacher notes compound – A substance consisting of elements that have reacted together or combined. electrode – A conductor which conducts electric charge into a liquid, gas or vacuum, or on to the surface of a solid body. electrolysis – The process of separating the elements within a compound using electricity. electrolyte – A solid substance which is dissolved or melted so it becomes ions in solution and a conductor of electricity. extraction – The process of separating the elements within a compound. ion – An atom that has gained or lost electrons and so carries a positive or negative charge. ionic substance – A substance containing ions, formed when a non-metal reacts with a metal. native metal – A metal that can be found in the Earth’s crust in its pure form, i.e. not requiring extraction. ore – A mineral from which a metal, usually found within a compound, can be extracted. oxidation – The loss of electrons from a substance. purification – The removal of impurities. reactant – A chemical element or compound that changes due to a chemical reaction to form a new compound. reactivity series – A list of metals in order of reactivity, with the most reactive metal at the top of the list, and the least reactive at the bottom. redox – A reaction where reduction and oxidation is taking place. reduction – The gain of electrons to a substance.

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Anagrams Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis

22 Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis
Multiple-choice quiz Boardworks GCSE Science: Chemistry Extracting Metals by Electrolysis Teacher notes This multiple-choice quiz could be used as a plenary activity to assess students’ understanding of extracting metals by electrolysis. The questions can be skipped through without answering by pressing the forward arrow. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.


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