What is roasting in metallurgy?

The moderately reactive metals such as iron, zinc, lead, copper, etc., are usually present as sulphides or carbonates in nature. The sulphide ores are converted into oxides by heating strongly below their melting point in the presence of excess air. This process is known as roasting. For example, the chemical reaction for the roasting of zinc ore is as follows: 2 ZnS s + 3 O 2 g → Heat 2 ZnO s + 2 SO 2 g

Molten cryolite is mixed with molten alumina in the extraction of aluminium by electrolysis. Why? Name the substances that are used as anode and cathode in this method.

Molten cryolite is mixed with molten alumina in the extraction of aluminium to reduce the melting point of alumina. The melting point is reduced from 2000 - 2500 ° C to 900 - 1000 ° C . Thus, it reduces some of the energy costs involved in the extraction of aluminium. Molten cryolite acts as a solvent for alumina and forms an electrolyte at low temperature which prevents the loss of aluminium in the form of vapours. Graphite rods are used as an anode and carbon lining is used as a cathode in this process. Aluminium metal is obtained at the cathode and oxygen gas is released at the anode.

Observe the following chemical equations: (i) Al 2 O 3 + 2 NaOH → 2 NaAlO 2 + H 2 O (ii) Al 2 O 3 + 6 HCl → 2 AlCl 3 + 3 H 2 O What is the conclusion that you take about the nature of aluminium oxide with the help of these equations? Give a reason for your conclusion.

Al 2 O 3 + 2 NaOH → 2 NaAlO 2 + H 2 O Al 2 O 3 + 6 HCl → 2 AlCl 3 + 3 H 2 O Aluminium oxide is reacting with base in the first equation to give salt & water and in the second equation, it is reacting with an acid to give salt and water. Thus, aluminium oxide is amphoteric in nature. Hence, it is an amphoteric oxide. Metal oxides that react with both acids as well as bases to produce salts and water are known as amphoteric oxides. Amphoteric oxides can neutralise both acids and bases.

Draw the diagram of an electrolytic cell used in the purification of copper and label the electrode having impure copper.

The above diagram shows the electrolytic cell used in the purification of copper. The anode is made of impure copper metal rod and the cathode is a pure copper metal rod. The electrolyte used in the reaction is acidified copper sulphate solution. On passing an electric current through the electrolyte, the metal ions from the anode migrate into the electrolyte and an equivalent amount of metal ion migrates from the electrolyte and deposits on the cathode. The soluble impurities go into the solution. The insoluble impurities settle down at the bottom as mud which is known as anode mud.