NCERT 8th Class (CBSE) Science: Coal and Petroleum

Question: Why is it necessary to use coal and petroleum economically?

Answer: There are two main reasons for which economical use of fossil fuels is necessary.

1. Fossil fuels are exhaustible sources. If they are used indiscriminately, they will be exhausted, as they are present in nature in limited amount. It takes millions of years to form fossil fuels, so it is not possible to make new fossil fuels artificially.
2. Secondly, fossil fuels specially coke, petrol, diesel, etc.,generate polluting gases on burning. Coke is almost carbon and produces carbon dioxide on burning, which pollutes the environment. These polluting emissions have given rise to danger of global warming and air pollution. So, their limited and economic use can control pollution and give better environment to live in.

Question: Write some ways in which we can conserve fossil fuels.

Answer: Economic and controlled consumption of fossil fuel can help conserving our natural resources. Following ways and measures can conserve our resources:

1. Vehicles should be driven at constant and moderate speed.
2. Engines should be switched off at traffic lights or other temporary halts.
3. Proper and regular maintenance of vehicles.
4. Vehicle pooling can reduce number of vehicles plying on road thus less consumption of fuel.
5. At home gas stoves should be cleaned properly and burners should not be left burning unnecessarily.
6. Pressure cookers should be preferred to pans. If pans are being used, they should be properly covered and their bottoms should not have deposits of burnt oil.
7. Small pans and burners should be used and pulses etc. should be soaked in water before cooking them

Question: Write some uses of coal tar.

Answer:  It is used as raw material for making various items – like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, naphthalene balls, etc. It is used for making the surface of roads.

Question: What happens after petroleum is taken out of oil well?

Answer: Crude oil needs to be processed to obtain useful products. After extraction from oil wells, petroleum is sent to oil refineries. Petroleum is subjected to fractional distillation in oil refinery. Various constituents of petroleum are separated through this process.