METALS - II : BRIEF ANSWERS

ANSWER IN BRIEF

*INDEX-TOPIC SEARCH

1. Explain : 'Earth - A treasure of Elements'.
   
   ANS:
   
   
   
   • Elements necessary for life are available in the form of minerals [native state or compound form] from all three main spheres of earth.
     
   • LITHOSPHERE consists of rocks and sand. It provides elements like aluminium, sodium, iron, calcium, copper, etc. in the form of their oxides and sulphides.
     
   • HYDROSPHERE consists of all water sources like seas, rivers, lakes, etc. It supplies elements like chlorine, bromine, sodium, potassium, magnesium, etc. in the form of their compounds.
     
   • ATMOSPHERE is the envelope of gases surrounding the earth. It provides nitrogen, oxygen, carbon dioxide, etc.
     
   
   Hence the earth is a treasure of elements for us.
   
   
2. Explain : Roasting giving examples.
   
   ANS: Roasting is a process in which the concentrated ore is heated for a longer period. This process is used to convert sulphide ore into oxide by removing sulphur. The volatile impurities are removed by roasting.
   
   
   
   
3. Describe the importance of Ultrapure metals.
   
   ANS: Modern science and technology require ultrapure elements for several specific applications. Elements like silicon, boron and germanium used as semiconductors, in space and in technology must be ultrapure. Elements like uranium used in nuclear field must also be ultrapure. Amount of boron in uranium is 1 ppm. Neutron produced during nuclear fission breaks boron atom and the chain reaction stops. A similar problem arises when germanium is used as semiconductor because it contains 1 ppm of copper. Such ultrapure elements are obtained by zone refining method or 'van Arkel' method.
   
   
4. Write in brief about the Fractional Refining Process (Zone Refining Process).
   
   ANS: The fractional refining process [zone refining process] is used to obtain ultrapure elements [metals with almost 100% purity] used in some specific applications like semiconductors, space technology, nuclear energy, etc. During the process impurities are removed on the basis of fractional crystallization. The impurities being more volatile remain in solution in molten state and their solubility decreases as the molten metal cools and can be separated in the form of crystals. This gives ultrapure element. Silicon, boron, germanium, etc.are obtained in ultrapure form by this method and are used in semiconductor technology.
   
   
5. Give the names of different steps of metallurgy.
   
   ANS: Different steps involved in metallurgy are :
   
   
   
   • Crushing and grinding of ore
     
   • Concentration or enrichment of ore
     
   • Roasting, calcination and smelting
     
   • Reduction
     
   • Refining and purification of metals
     
   
   
6. Distinguish between roasting and calcination.
   
   ANS: