CBSE Class 8 Science Coal and Petroleum Chapter Notes. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.
COAL & PETROLEUM
We use various materials for our basic needs. Some of them are found in nature and some have been made by human efforts. The variety of substances that man gets from earth and nature to meet his basic needs are called natural resources.
Types of Natural Resources :
These are two types namely renewable and non-renewable.
Fossil fuels : Exhaustible natural resources like coal , petroleum or natural gas were formed from the dead remains of living organism (fossils). So , these are called fossil fuels. Coal and petroleum are very important natural resources and play a vital role in modern society. They are found in the earth's crust.
Coal : Coal is a complex mixture of carbon, hydrogen and oxygen compounds. Some nitrogen, sulphur and phosphorus compounds are also present in it. It is found in coal mines deep under the surface of earth.
Occurence of coal : Russia, China, UK. Germany, Africa and Australia have rich deposits of coal. In India, big coal mines are found at Jharia and Bokaro in Jharkhand and Raniganj in West Bengal.
Types of coal :
The different varieties of coal with varying carbon content are given below in table
Formation : It is believed that millions of years ago, the ground below the forests was split open by natural forces such as earthquakes and volcanoes. The forests were buried in the chasms. Thus, the plants had no contact with oxygen. Successive layers of sediments sealed the buried plants. Over millions of years these deposits were subjected to tremendous pressure and heat which finally transformed them into coal.
Carbonisation : The chemical process involved in the transformation of plant matter into coal is called the carbonisation of plant matter.
Destructive distillation of coal : The process of heating coal in the absence of air is called the destructive distillation of coal. Coal contain a number of elements such as carbon, hydrogen, oxygen, nitrogen and sulphur. When coal is heated in the absence of air, a number of products are obtained.
The main products obtained by the destructive distillation of coal are as follows :
(i) Coke (ii) Coal tar (iii) Ammoniacal liquor (iv) Coal gas
(i) Coke : Coke contains 98% carbon. It is porous , tough black and the purest form of coal. Like charcoal, it is a good fuel and burns without smoke. But it is seldom employed as a fuel because it can be put to more valuable use. It is largely employed as a reducing agent in the extraction of metals from their ores, It is also used in making fuel gases like water gas and producer gas.
DO YOU KNOW?
Water gas is an equimolar mixture of carbon monoxide and hydrogen. (CO + H2) Producer gas is a mixture of carbon monoxide and nitrogen. (CO + N2)
(ii) Coal tar : Coal tar is a mixture of different carbon compounds. It is a thick, black liquid with unpleasant smell. The fractional distillation of coal tar gives many chemical substances which are used in the preparation of dyes, explosives, paints, synthetics fibres, drugs, and pesticides. Some of these chemical substances are benzene, toluene, phenol and aniline. Naphthalene balls used to repel moth and other insects are also obtained from coal tar. Bitumen is used in place of coal tar for metalling the roads.
(iii) Ammoniacal liquor : The ammonia produced as a result of destructive distillation of coal is absorbed in water. The aqueous solution of ammonia, i.e. ammonium hydroxide solution , is called ammoniacal liquor. It is used in the preparation of fertilizers such as ammonium sulphate and ammonium superphosphate.
(iv) Coal gas : Coal gas is mainly a mixture of hydrogen, methane and carbon monoxide. The gases present in coal gas are combustible, and hence it is an excellent fuel. It has high calorific value. It was used for lighting houses, factories and streets in Mumbai until 1950. It was also used for cooking until recently.
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