Class 8 Science Chapter 3 Question Answers - Coal and Petroleum

Q1: Define the term ‘petrochemicals’.
Ans: Petrochemicals are substances derived from petroleum and natural gas. They are used in the production of detergents, fibers, plastics, and other industrial products.

Q2: What is CNG? What are its uses?
Ans: CNG stands for Compressed Natural Gas. It is natural gas stored under high pressure. CNG is used for power generation and as a fuel for vehicles. It is considered a cleaner fuel option for transportation due to lower emissions compared to traditional gasoline or diesel.

Q3: What is coal? Write its two uses.
Ans: Coal is a hard, black combustible substance that mainly contains carbon.
Uses:

• It is used as a fuel in homes and industries.
• It is used as a fuel at Thermal Power Plants for generating electricity.

Q4: What is fuel?
Ans: Anything that burns to produce energy in an efficient manner is called a fuel.

Q5: Explain about coal tar.
Ans: Coal tar is produced when coal is heated in the absence of air. It is a thick, viscous liquid with a pungent smell. It is a mixture of various compounds including benzene, toluene, naphthalene, and phenol.

Q6: Where do we get coal and how is it formed?
Ans: Coal is obtained from coal mines deep within the earth's crust. It is formed from the slow decomposition of dead trees and other plant matter buried under high pressure and temperature over millions of years.

Q7: Give a brief description of peat.
Ans: Peat is the least advanced and softest form of coal. It has a low carbon content and a significant amount of moisture. It is not very suitable for use as fuel. Its carbon content is around 20 – 25%.

Q8: Name two products obtained from the destructive distillation of coal. What is the residue left in this process? Give one main use of this residue.
Ans: The two main products obtained from the destructive distillation of coal are coal gas and coal tar. The residue left in this process is coke. Coke is mainly used as a reducing agent in the extraction of metals.

Q9: Name three constituents of petroleum and write their uses also.
Ans: The three constituents of petroleum are:

• Petrol: Used as a motor fuel and for dry cleaning.
• Paraffin wax: Used for making ointments, candles, vaseline, etc.
• Diesel: Used as a fuel for heavy motor vehicles and electric generators.

Q10: Define fossil fuels. Give examples.
Ans: Natural fuels that are formed by the burial of living organisms deep underground for an extended period of time are called fossil fuels.
For example, coal, petroleum, natural gas.

Q11: List the steps to conserve the resources.
Ans: As we know, we all are dependent on the resources. But we should keep in mind that resources are limited in nature. If we misuse it, our future generation will have no resources. This is an alarming situation.
We can take following steps:

• We shbuld cook our food on low flame.
• Devices that consume less energy like CFLs and LED lights should be preferred.
• We should take care not to waste electricity.
• We should cover our cooking vessels while cooking.
• Instead of use of individual vehicles, use of public transport should be encouraged.
• Solar or tidal energy should be developed and encouraged.
• Dams should be use to generate electricity instead of burning coal or petroleum.
• Public awareness programmes should be conducted.

Q12: Write a short note on petroleum.
Ans: Petroleum is the liquid form of fuel. It is also known as crude oil and found trapped between the layers of impervious rocks under the ground. It is a natural resource, which formed by the dead plants and animals in the sea. It is a dark coloured viscous liquid and like all other oils, it is lighter than water. It is a mixture of different hydrocarbons. It undergoes fractional distillation to yield petrol, kerosene, diesel and other chemicals used in manufacture of plastics.

Q13: Explain about the varieties of coal.
Ans: Depending upon the amount of carbon content, coal may be of four types:

• Peat: This is the most inferior and softest form of coal. Its carbon content is very low. It has a large amount of moisture and is not much suitable to be used as fuel.
• Lignite: Lignite is comparatively harder than peat, but still is very soft. Its carbon content is more than that of peat.
• Bituminous: Its carbon content is higher, as it is free from moisture and other impurities.
• Anthracite: This is the highest grade coal. This is also known as hard coal. It has maximum amount of carbon. It produces a very little smoke.

Q14: The burning of fossil fuels causes air pollution. Explain.
Ans:

• The burning of fossil fuels causes a lot of air pollution.
• The burning of coal produces gases like carbon dioxide, carbon monoxide, sulphur dioxide, etc., which can lead to undesirable changes in climate due to increase greenhouse effect.
• The major air pollutants produced by the burning of petrol in automobiles are carbon monoxide, sulphur dioxide, unbumt hydrocarbons, etc. These pollutants are harmful for human beings and living organisms which causes breathing problems and skin diseases.

Q15: How is the energy useful to us? Explain.
Ans: We need energy in almost every field of our life. Without energy our life is impossible. Some of the uses of energy are:

• We need energy of fuels to generate electricity and to run vehicles.
• We need energy to run our electrical appliances like refrigerator, TV, radio, computer, etc.
• We need energy at construction sites to construct houses, buildings, etc.
• We need energy to cook our food and other domestic use.
• We need energy (petrochemicals) for manufacturing fibres, plastics, paints, cosmetics, etc.
• All the factories, industries, agricultural devices depend on power supply to run the machines.