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SAI International School

Subject - Chemistry

Class - VIII

Topic – Coal and Petroleum

Sub-Topic – Petroleum

LESSON NOTES

Petroleum:

 The name ‘petroleum’ means rock oil. Petra means rock and Oleum means oil. It is called

petroleum because it is found under the crust of the earth trapped in rocks.
 Petroleum is a dark coloured, thick crude oil found deep below the ground trapped in the

rocks.
 It is a complex mixture of hydrocarbons. It is insoluble in water.

How Petroleum was Formed?

 It was formed by the decomposition of the remains of tiny plants and animals buried under

the sea millions of years ago.
 Their bodies sank to the bottom of the sea and were soon covered by the mud and sand.

 Due to high pressure, heat and action of bacteria and in the absence of air, the dead
remains of plants and animals were slowly converted to petroleum and natural gas.

 The petroleum thus formed got trapped between the layers of impervious rocks (non-

porous), forming an oil deposit. Petroleum is lighter than water, so it floats over water.
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