Reduction Of Aluminium Oxide

Reduction of Aluminium Oxide

Aluminium cannot be extracted by heating with carbon, because it is too reactive. Instead, it is extracted by electrolysis. When ionic compounds are dissolved or melted the ions are free to move about. If an electric current is passed through the liquid the positive ions move to the negative electrode where they gain electrons. The negative ions move to the positive electrode where they lose electrons. During electrolysis gases may be given off or metals deposited at the electrodes. The raw material for producing aluminium is aluminium oxide, purified from an aluminium ore called bauxite. Aluminium oxide has a very high melting point, so it is dissolved in a molten aluminium compound called cryolite. This does not use so much heat energy, so is cheaper because cryolite has a lower melting point. The electrodes are made of carbon. 1. Aluminium oxide (Al2O3) is an ionic compound where each oxygen atom gains 2 electrons. a. What is the charge on each aluminium ion? b. Which electrode will these be attracted to? 2. Why is the aluminium oxide dissolved in cryolite? 3. Which ion is attracted to the anode? a. How many electrons does this ion gain/lose when it reaches the anode? b. This atom reacts with the anode to form carbon dioxide. Write a balanced chemical equation with state symbols for this reaction. c. What will happen to the anode over time? What does this mean for the cost of extracting aluminium? 4. Aluminium is one of the most abundant materials in the Earths crust. Why is it relatively expensive compared to less common materials (look at the costs of the reduction process)?