Some general notes on electrolysis AND. Electrolysis of acidified water dilute sulfuric acid 3. Electrolysis of sodium chloride solution brine 4. Electrolysis of copper II sulfate solution and electroplating 5.
Electrolysis of molten lead II bromide and other molten compounds 6. Electrolysis of copper II chloride solution 7. Electrolysis of hydrochloric acid 8. Summary of electrode equations and products 9.
Summary of electrolysis products from various electrolytes Simple cells batteries Fuel Cells The extraction of aluminium from purified molten bauxite ore Anodising aluminium to thicken and strengthen the protective oxide layer The extraction of sodium from molten sodium chloride using the 'Down's Cell' The purification of copper by electrolysis The purification of zinc by electrolysis Electroplating coating conducting surfaces with a metal layer Electrolysis calculations.
Reactivity of metals : all the reactions of metals with oxygen air , water and acids, displacement reactions Oxidation—reduction explained redox theory Group 1 Alkali Metals: chemical and physical properties Extra Industrial chemistry : properties and uses of metals including titanium and aluminium Transition metals physical and chemical properties and uses Metallic Bonding — structure and properties of metals.
Extra Electrochemistry—electrolysis theory, experiment designs and links to all electrolysis sections Doc Brown's. Doc Brown's Chemistry. Enter chemistry words e. Metal extraction index 1. Introduction to Metal Extraction 2. Extraction of Iron and Steel Making 3. Extraction of Aluminium and Sodium this page 4. Extraction of Lead, Zinc, Titanium and Chromium 6. Extraction of Aluminium The current method for extracting aluminium is expensive because it involves several stages and uses large amounts of costly electrical energy.
Aluminium is theoretically a very reactive metal, so, because its position in the reactivity series of metals, aluminium cannot be extracted using carbon because it is above carbon in the reactivity series ie more reactive than carbon in the series. Carbon is not reactive enough to displace aluminium from its compounds such as aluminium oxide.
So, if aluminium is too reactive to be obtained by carbon reduction of its oxide another method must be employed which is called electrolysis. Aluminium is obtained from mining the mineral bauxite which is mainly aluminium oxide Al 2 O 3 and bauxite must be purified prior to electrolysis, adding to the manufacturing costs. Aluminium oxide is insoluble in water, so it must be molten to act as an electrolyte. However, the melting point of aluminium oxide is high. A lot of energy must be transferred to break its strong ionic bonds , and this is expensive.
To reduce costs, powdered aluminium oxide is dissolved in molten cryolite. This ionic compound melts at a lower temperature than aluminium oxide, reducing costs.
However, significant amounts of energy are required to melt the cryolite. The diagram shows an electrolysis cell used to extract aluminium. The negative electrodes cathodes and the positive electrodes anodes are made of graphite, a form of carbon.
During electrolysis:. The oxygen reacts with the carbon in the electrodes, forming carbon dioxide which bubbles off. Carbon is therefore lost from the positive electrodes, so they must be replaced frequently.
This adds to the cost of the process. The high cost of the process because of the huge amounts of electricity it uses. This is so high because to produce 1 mole of aluminium which only weighs 27 g you need 3 moles of electrons.
You are having to add a lot of electrons because of the high charge on the ion to produce a small mass of aluminium because of its low relative atomic mass. Energy and material costs in producing the cryolite, some of which gets lost during the electrolysis.
Loss of landscape due to the size of the chemical plant needed, and in the production and transport of the electricity. Atmospheric pollution from the various stages of extraction. For example: carbon dioxide from the burning of the anodes greenhouse effect ; carbon monoxide poisonous ; fluorine and fluorine compounds lost from the cryolite during the electrolysis process poisonous.
Saving of raw materials and particularly electrical energy by not having to extract the aluminium from the bauxite. Offsetting these to a minor extent Energy and pollution costs in collecting and transporting the recycled aluminium. Aluminium is usually alloyed with other elements such as silicon, copper or magnesium.
Pure aluminium isn't very strong, and alloying it adds to it strength. This layer can be strengthened further by anodising the aluminium. Anodising essentially involves etching the aluminium with sodium hydroxide solution to remove the existing oxide layer, and then making the aluminium article the anode in an electrolysis of dilute sulphuric acid.
The oxygen given of at the anode reacts with the aluminium surface, to build up a film of oxide up to about 0.
As well as increasing the corrosion resistance of the aluminium, 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 aluminium articles with the colour built into the surface.
If this is the first set of questions you have done, please read the introductory page before you start. Extracting aluminium from bauxite Introduction Aluminium is too high in the electrochemical series reactivity series to extract it from its ore using carbon reduction.
Aluminium ore The usual aluminium ore is bauxite. Purifiying the aluminium oxide - the Bayer Process Reaction with sodium hydroxide solution Crushed bauxite is treated with moderately concentrated sodium hydroxide solution. Precipitation of aluminium hydroxide The sodium tetrahydroxoaluminate solution is cooled, and "seeded" with some previously produced aluminium hydroxide. Conversion of the aluminium oxide into aluminium by electrolysis The aluminium oxide is electrolysed in solution in molten cryolite , Na 3 AlF 6.
The electrolysis cell The diagram shows a very simplified version of an electrolysis cell. The electrode reactions These are very complicated - in fact one source I've looked at says that they aren't fully understood. This is the simplification: Aluminium is released at the cathode.
Aluminium ions are reduced by gaining 3 electrons.
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