CLASS XII CHAPTER 6 General Principles and isolation
INTRODUCTION
We have archaeological evidence of the use of different metals since ancient times. Evidence shows that different metals were used in different parts of the country. For example, Harappans used gold, silver and their alloys for making ornaments etc. Recent excavation by the archaeological department of India has shown that Iron was used in 1800 BCE. The use of other metals has also been proved.
Archaeological evidence is available of zinc production in Rajasthan mines at Zawar from the 6th or 5th BCE. India was the first country to master zinc distillation. Because of its low boiling point, zinc tends to vaporise while its ore is smelted. Pure zinc could be produced after a sophisticated ‘downward’ distillation technique in which the vapour was condensed in a lower container. The same method was applied to mercury also. Indian metallurgists were masters in this technique. We can find this description in Sanskrit texts of the 14th century.
For obtaining a particular metal, first, we look for minerals which are naturally found chemical substances in the earth’s crust which are extracted through mining. Out of many minerals, only a few can be used to extract metal profitably and economically. These minerals are known as ores.
Some elements like carbon, sulphur, gold and noble gases, occur in a free state while others are found in combined forms in the earth’s crust. Elements vary in abundance. Among metals, aluminium is the most abundant. In fact, it is the third most abundant element in the earth’s crust. It is a primary component of many igneous minerals including mica and clays. Many gemstones are impure forms of Al2O3. For example, gems ‘ruby’ and ‘sapphire’ have Cr and Co respectively as impurities. The second most abundant metal in the earth’s crust is Iron. It forms a variety of compounds and their various uses make it a very important element. It is one of the essential elements in biological systems as well.
In the following chapter, we will learn about the modern methods of extraction of elements.
CONTENT
Occurrence of Metals
Concentration of Ores
Extraction of Crude Metal from Concentrated Ore
Thermodynamic Principles of Metallurgy
Electrochemical Principles of Metallurgy
Oxidation Reduction
Refining
Uses of Aluminium, Copper, Zinc and Iron
ICSE class XII chapter 6 general principles and isolation