Explain the electrochemical reduction method to obtain aluminium from alumina with diagram.

Electrolysis of alumina is carried out in an electrolytic cell at a much lower temperature by dissolving it in molten cryolite ( Na 3 AlF 6 ) and fluorspar ( CaF 2 ) . The addition of cryolite, and fluorspar reduces the melting point to about 1000 0 C . The electrolytic cell is a large steel tank having a lining of carbon (graphite) on the inner side. The carbon (graphite) lining acts as a cathode. A set of carbon (graphite) rods dipped in the molten electrolyte acts as an anode. On passing electric current, electrolysis of alumina takes place. Aluminium is formed at the cathode and oxygen gas is liberated at the anode. The electrode reactions are as follows:Cathode: Al 3 + + 3 e - → Al ( l ) (Reduction) Anode: 2 O 2 - → O 2 + 4 e - (Oxidation) The molten aluminium is heavier than the electrolyte used and hence, it sinks to the bottom of the tank from where it is removed periodically. The oxygen gas liberated at the anode reacts with the carbon anode and forms carbon dioxide gas. C ( s ) + O 2 ( g ) → CO 2 ( g ) As anode gets oxidised during the electrolysis of alumina, it has to be replaced from time to time.

Explain the liquefaction and zone refining method of refining of metals. (draw diagram)

Zone melting (or zone refining) is a group of similar methods of purifying crystals, in which a narrow region of a crystal is melted, and this molten zone is moved along the crystal. The molten region melts impure solid at its forward edge and leaves a wake of purer material solidified behind it as it moves through the ingot. The impurities concentrate in the melt, and are moved to one end of the ingot. Liquefaction of gases is the physical conversion of a gas into a liquid state. When pressure on a gas is increased, its molecules are closer together, and its temperature is reduced, which removes enough energy to make it change from the gaseous to the liquid state.

Give the rules for how much metal is deposited on the electrode in the process of electrolysis?

Faraday’s First Law of Electrolysis states that “The mass of a substance deposited at any electrode is directly proportional to the amount of charge passed.” Mathematically it can be expressed as follows – m = ZQ Where m = mass of a substance (in grams) deposited or liberated at an electrode Q = amount of charge (in coulombs) or electricity passed through it Z is the proportionality constant Faraday’s Second Law of Electrolysis states that “the mass of a substance deposited at any electrode on passing a certain amount of charge is directly proportional to its chemical equivalent weight.” w α E Where w = mass of the substance E = equivalent weight of the substance