Class 8 Science Coal And Petroleum Worksheets
FAQs on Class 8 Science Coal And Petroleum Worksheets
1. What are fossil fuels, and why are they classified as exhaustible natural resources? This is a frequently asked question for exams.
Fossil fuels are natural fuels, such as coal, petroleum, and natural gas, formed in the Earth's crust from the remains of dead plants and animals over millions of years. They are classified as exhaustible natural resources because they are present in limited quantities and cannot be replenished quickly once consumed. Their formation is an extremely slow process, making their conservation an important topic for the CBSE Class 8 Science exam 2025-26.
2. Describe the formation of coal. Why is this process called carbonisation? (3 Marks)
Coal was formed millions of years ago when dense forests got buried under the soil due to natural processes like floods. The process is as follows:
- Over time, more soil deposited over the buried forests.
- They were compressed under immense pressure and high temperature.
- Under these conditions, the dead vegetation slowly converted to coal.
3. Explain the process of petroleum refining and list four important products obtained from it. (5 Marks)
Petroleum is a dark, oily liquid mixture of various substances. The process of separating its various constituents or fractions is called petroleum refining. This is carried out in a petroleum refinery using the method of fractional distillation, which separates components based on their different boiling points. Four important products obtained are:
- Petrol: Used as a fuel for light motor vehicles.
- Diesel: Used as a fuel for heavy motor vehicles and electric generators.
- Kerosene: Used as a fuel for stoves, lamps, and for jet aircraft.
- Lubricating Oil: Used for lubrication in machines and engines.
4. Petroleum is often called 'black gold'. Justify this statement from an exam perspective.
Petroleum is called 'black gold' due to its high commercial value and wide range of uses. The term 'black' refers to its crude, unrefined colour, while 'gold' signifies its immense economic importance, similar to the precious metal. Many useful substances, known as petrochemicals, are derived from it, which are used to manufacture detergents, synthetic fibres (polyester, nylon), plastics, and other valuable materials. Its importance makes this a frequently asked higher-order thinking (HOTS) question.
5. What is CNG, and why is it considered an important alternative fuel for vehicles?
CNG stands for Compressed Natural Gas. It is natural gas stored under high pressure. CNG is considered an important alternative fuel for vehicles for the following key reasons:
- Less Polluting: It is a cleaner fuel because it burns more completely and produces significantly fewer harmful gases like carbon monoxide and sulphur dioxide compared to petrol or diesel.
- Direct Supply: It can be supplied directly to homes and factories through a network of pipes, which is a major advantage.
- Cost-Effective: It is generally cheaper than petrol and diesel.
6. Why should we use fossil fuels like coal and petroleum judiciously? Explain this important concept.
It is extremely important to use fossil fuels judiciously for two main reasons:
- Limited Availability: Coal and petroleum are exhaustible resources. It took millions of years for them to form, but we are consuming them at a very rapid rate. They will eventually run out if we do not conserve them.
- Environmental Pollution: The burning of these fuels releases harmful gases like carbon dioxide, sulphur dioxide, and nitrogen oxides into the atmosphere. This contributes to major environmental problems such as air pollution, acid rain, and global warming.
7. Coal and petroleum are both formed from the remains of ancient organisms. What is the fundamental difference in their origin that makes one a solid and the other a liquid?
The fundamental difference lies in the type of organic matter they were formed from and the environment of their formation.
- Coal is a solid fuel primarily formed from the remains of terrestrial plants and trees in swampy, forest-like environments. The decomposition of this dense plant material under heat and pressure resulted in a carbon-rich solid.
- Petroleum is a liquid fuel formed from the remains of tiny marine organisms like plankton and algae. When these organisms died, they settled on the ocean floor and were buried under layers of sand and silt. The heat and pressure in this marine environment transformed them into a liquid and gaseous state (crude oil and natural gas).
8. List three important products obtained from the processing of coal and state one use for each.
When coal is processed in the industry, several useful products are obtained. Three important ones are:
- Coke: It is a tough, porous, and almost pure form of carbon. It is a crucial component in the manufacture of steel and the extraction of many metals.
- Coal Tar: It is a thick, black liquid with an unpleasant smell. It is a mixture of about 200 substances and is used as a starting material for manufacturing synthetic dyes, drugs, explosives, and plastics.
- Coal Gas: It is obtained during the processing of coal to get coke. It is used as a fuel in many industries situated near coal processing plants.
