Question

Define Roasting.
(A) Heating of sulphide ores in the presence of excess air to convert them into oxides
(B) Heating of carbonate ores in the limited supply of air to convert them into oxides
(C) Heating of oxides of metal to turn them into metal
(D) Heating of carbonate ores in the limited supply of air to convert them into oxides

Answer 1

In the process of roasting, the oxidation number of metals does not change. In the process of roasting the gas which is produced as a side product can be used in the production of a mineral acid.

Complete step by step solution:
Roasting is a method to obtain metal oxides by reaction of some compounds with oxygen.
- So, we can allow the sulphides of the metal to react with oxygen gas in excess of air to give metal oxides. This process is called roasting.
- Thus, the ores which contain metal in its form of sulphides are heated at a temperature below its melting point and allowed to react with the oxygen.
As an example,
$2ZnS+3{{O}_{2}}\to 2ZnO+2S{{O}_{2}}$
Here, Zinc sulphide reacts with oxygen when heat is given to give zinc oxide and sulphur dioxide gas.
- When roasting of copper ores is done, a special furnace which is named as a reverberatory furnace is used.
- In this roasting process, if the ores contain impurity of iron, then we can add silica to it and iron will get removed as slag.

So, the correct answer to this question is (A).

Note: Do not get confused between calcination and roasting. In calcination, the compound is heated and the volatile matter present in the compound gets removed and we obtain metal oxide as a product.