ICSE Class 8 Answered

Formation of Coal

·Coal was formed about 200 to 300 million years ago from the remains of plants such as ferns, moss and trees which existed in swampy forests.

·As plants and trees died, their remains sank to the bottom of swampy areas.

·These dead plants and trees got covered with a layer of mud, water, rocks and soil by accumulating layer upon layer over a period of time. This eventually formed a soggy and dense material called as Peat.

·As more and more matter piled up on them, the bottom layers got compressed.

·Increasing heat and pressure from the top layers along with bacterial action gradually changed the material to coal.

·With the formation of each successive layer of coal, the amount of carbon present in the deposit increased and the level of impurities decreased.

·This gradual process of conversion of vegetable matter into coal under high temperature and pressure is called Carbonisation

Types of Coal

Peat

•The heat and pressure from the top layers converts dead plants into a spongy brown material called Peat.

•Peat is the first stage in the formation of coal.

•It is light brown in colour and contains only about 50% - 60% carbon. therefore, it is the most inferior form of coal.

Lignite

•It is the second stage in the formation of coal. The peat is compressed between sediment layers to form Lignite.

•Lignite contains 60% - 70% carbon.

•It is also brown in colour, but it is harder than peat.

Bituminous

•It is the third stage in the formation of coal. It contains 80% - 90% carbon.

•There are high, medium and low varieties of bituminous coal, with carbon content being 90%, 80% and 70%-75% respectively.

•Bituminous coal is the most common variety of coal and is also known as household coal. It is black and hard. On heating it, both volatile and non-volatile materials are given out.

Anthracite

•It is the purest variety of coal. It is the oldest stage in the formation of coal. Its carbon content varies between 92-98%.

•It is hard, dense and black.It is difficult to ignite, but once ignited it burns with a lot of heat and for a very long time.

•It is found in very few places in the world. Anthracite does not produce any ash and is considered as the best quality of a coal.

Uses of coal

1.Coal is used in various industries as both domestic and an industrial fuel, that is, in homes, thermal power stations and furnaces.

2.It is processed in the industry to obtain useful products such as coke, coal tar and coal gas.

3.It is used in the manufacture of synthetic petrol.

4.It is also an important requirement for the manufacture of some fertilizers, drugs, rubber, wax, synthetic textiles and perfumes.

5.It is used as a source of many organic compounds such as benzene, naphthalene, aniline, etc.