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View all posts Register Sign In Sherpa Find a Tutor Messages Pending Bookings Upcoming Bookings Become a TutorHelp Center Free Lessons Q&A Forum Blog Sign up Existing user? Sign in Thanks for the response!Each time you help a student, your tutor score is boosted, improving your ranking in search results. How does this work? Chemistry > GCSE > Extracting Metals > Why isn't ... Question 1 year ago · {{ replyCount }} Replies · 1136 views R Rodrick Skiles 1 Reply {{ replyCount }} Replies Carola Best Answer! Verified Sherpa Tutor Aluminium is too reactive. That's why electrolysis is used to extract aluminium from aluminium oxide. See also https://www.bbc.co.uk/bitesize/guides/zpcdsg8/revision/2. Experienced GCSE Science and A level Chemistry tutor with Phd Interested in booking a 1-1 lesson with me? Click here to view my profile and send me a message. Got the answer? Help Rodrick out. Back To Chemistry Back To Chemistry GCSE Back To Topic Need help with Chemistry?We have thousands of qualified teachers who are able to provide top quality lessons online. Find your tutor and set up your free introduction today! Find a Chemistry Tutor Related QuestionsHow is reactivity related to an atoms outer shell? What does the rate of bubbles that hydrogen give off during a reaction suggest? How reactive are the metals at the top of the reactivity series? Why are most metals found on earth compounds? What ia the most common element that reacts with metals? This page starts by looking at the extraction of aluminum from its ore, bauxite, including some economic and environmental issues. It finishes by looking at some uses of aluminum. Aluminum is too high in the electrochemical series (reactivity series) to extract it from its ore using carbon reduction. The temperatures needed are too high to be economic. Instead, it is extracted by electrolysis. The ore is first converted into pure aluminum oxide by the Bayer Process, and this is then
electrolyzed in solution in molten cryolite - another aluminum compound. The aluminum oxide has too high a melting point to electrolyse on its own. The usual aluminum ore is bauxite. Bauxite is essentially an impure aluminum oxide. The major impurities include iron oxides, silicon dioxide and titanium dioxide. Crushed bauxite is treated with moderately concentrated sodium hydroxide solution. The concentration, temperature and pressure used depend on the source of the bauxite and
exactly what form of aluminum oxide it contains. Temperatures are typically from 140°C to 240°C; pressures can be up to about 35 atmospheres. High pressures are necessary to keep the water in the sodium hydroxide solution liquid at temperatures above 100°C. The higher the temperature, the higher the pressure needed. With hot concentrated sodium hydroxide solution, aluminum oxide reacts to give a solution of sodium tetrahydroxoaluminate. \[ Al_2O_3 + 2NaOH + 3H_2O \longrightarrow
2NaAl(OH)_4\] The impurities in the bauxite remain as solids. For example, the other metal oxides present tend not to react with the sodium hydroxide solution and so remain unchanged. Some of the silicon dioxide reacts, but goes on to form a sodium aluminosilicate which precipitates out. All of these solids are separated from the sodium tetrahydroxoaluminate solution by filtration. They form a "red mud" which is just stored in huge lagoons. The sodium tetrahydroxoaluminate solution is cooled, and "seeded" with some previously produced aluminum hydroxide. This provides something for the new aluminum hydroxide to
precipitate around. \[ NaAl(OH)_4 \longrightarrow Al(OH)_3 + NaOH \] Formation of pure aluminum oxide Aluminum oxide (sometimes known as alumina) is made by heating the aluminum hydroxide to a temperature of about 1100 - 1200°C. \[ 2Al(OH)_3 \longrightarrow Al_2O_3 + 3H_2O \] Conversion of the aluminum oxide into aluminum by electrolysis The aluminum oxide is electrolyzed in solution in molten cryolite, Na3AlF6. Cryolite is another aluminum ore, but is rare and expensive, and most is now made chemically. The electrolysis cellThe diagram shows a very simplified version of an electrolysis cell. Although the carbon lining of the cell is labelled as the cathode, the effective cathode is mainly the molten aluminum that forms on the bottom of the cell. Molten aluminum is syphoned out of the cell from time to time, and new aluminum oxide added at the top. The cell operates at a low voltage of about 5 - 6 volts, but at huge currents of 100,000 amps or more. The heating effect of these large currents keeps the cell at a temperature of about 1000°C. The electrode reactionsThese are very complicated - in fact one source I've looked at says that they aren't fully understood. For chemistry purposes at this level, they are always simplified (to the point of being wrong! - see comment below). This is the simplification: Aluminum is released at the cathode. Aluminum ions are reduced by gaining 3 electrons. \[ Al^3+ + 3e^- \longrightarrow Al\] Oxygen is produced initially at the anode. \[ 2O^{2-} \longrightarrow O_2 + 4e^-\] However, at the temperature of the cell, the carbon anodes burn in this oxygen to give carbon dioxide and carbon monoxide. Continual replacement of the anodes is a major expense. Some economic and environmental considerations This section is designed to give you a brief idea of the sort of economic and environmental issues involved with the extraction of aluminum. I wouldn't claim that it covers everything! Think about:
Environmental problems in mining and transporting the bauxite Think about:
Extracting aluminum from the bauxite Think about:
RecyclingThink about:
Uses of aluminumAluminum is usually alloyed with other elements such as silicon, copper or magnesium. Pure aluminum isn't very strong, and alloying it adds to it strength. Aluminum is especially useful because it
Anodizing essentially involves etching the aluminum with sodium hydroxide solution to remove the existing oxide layer, and then making the aluminum article the anode in an electrolysis of dilute sulphuric acid. The oxygen given of at the anode reacts with the aluminum surface, to build up a film of oxide up to about 0.02 mm thick. As well as increasing the corrosion resistance of the aluminum, this film is porous at this stage and will also take up dyes. (It is further treated to make it completely non-porous afterwards.) That means that you can make aluminum articles with the colour built into the surface. Some uses include:
Why is it not possible to reduce aluminium using carbon?Why can't aluminium be reduced by carbon ? Solution : Carbon has a greater reduction potential than aluminium i.e., carbon has a greater tendency than aluminium to get reduced.
Why is electrolysis of is used to extract aluminum rather than reduction using carbon?Aluminium is more reactive than carbon and has more affinity towards oxygen. So aluminium can not be reduced by using carbon. Electrolysis is the best method for extraction.
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