Living Science Solutions for Class 8 Science Chapter 5 Coal And Petroleum are provided here with simple step-by-step explanations. These solutions for Coal And Petroleum are extremely popular among class 8 students for Science Coal And Petroleum Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Living Science Book of class 8 Science Chapter 5 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Living Science Solutions. All Living Science Solutions for class 8 Science are prepared by experts and are 100% accurate.

Page No 74:

Question 1:

Renewable resources need to be conserved because
(a) we are using them faster than they are replenished by nature.
(b) they are slowly disappearing from the earth.
(c) if we overuse them nature will stop replacing them.
(d) all of these

Answer:

(d) all of these
Renewable resources need to be conserved because non-renewable resources such as coal, petroleum and natural gas take millions of years to form naturally. Moreover, they cannot be replaced as quickly as they are being consumed.

Page No 74:

Question 2:

It is an important fraction of petroleum. It is further distilled to get lubricating oil and paraffin wax.
(a) petroleum gas
(b) heavy oil
(c) anthracite
(d) residue

Answer:

(d) residue
Residue is that component of petroleum which is collected at the bottom of the tower. It can be further distilled separately to obtain lubricating oil and paraffin wax. 

Page No 74:

Question 3:

Coal mainly contains
(a) carbon.
(b) carbon and hydrogen.
(c) carbon, hydrogen and nitrogen.
(d) carbon, nitrogen and oxygen.

Answer:

(a) carbon
Coal is mainly composed of carbon. It may also contain varying amounts of hydrogen, oxygen, nitrogen and sulphur.

Page No 74:

Question 4:

Which of the following is regarded as the best variety of coal?
(a) bituminous
(b) lignite
(c) anthracite
(d) peat

Answer:

(c) anthracite
Anthracite coal has the highest carbon content and is the cleanest form of coal.

Page No 74:

Question 5:

Which of the following is a non-polluting fuel for vehicles?
(a) petrol
(b) diesel
(c) kerosene
(d) CNG

Answer:

(d) CNG
CNG is a natural gas stored under high pressure. Burning of natural gas produces nitrogen oxides, sulphur dioxide, carbon dioxide and carbon monoxide in low quantities than that produced during the burning of coal or oil. Thus, it is a non-polluting fuel.

Page No 74:

Question 6:

In destructive distillation, coal is heated strongly to about
(a) 5000 °C.
(b) 1000 °C.
(c) 100 °C
(d) 10,000 °C.

Answer:

(b) 1000°C
In destructive distillation of coal, coal is heated at 1000°C in the absence of air to produce coal tar, coal gas, coke and liquor ammonia as main by products.

Page No 74:

Question 7:

Which of these is not a natural source of energy?
(a) coal
(b) petroleum
(c) electricity
(d) sun

Answer:

(c) electricity
Electricity is generated by man using natural resources; therefore, it is not a natural source of energy.

Page No 74:

Question 8:

Fossil fuels are
(a) renewable but exhaustible.
(b) renewable and inexhaustible.
(c) non-renewable but can be recycled.
(d) non-renewable and cannot be recycled.

Answer:

(d) non-renewable and cannot be recycled
Fossil fuels are non-renewable and cannot be recycled because they are formed extremely slowly (in millions of years) from dead remains of living organisms and their rate of consumption is more than their rate of replenishment.

Page No 74:

Question 9:

Which of these is not a fossil fuel?
(a) CNG
(b) LPG
(c) petrol
(d) hydrogen

Answer:

(d) Hydrogen

Fossil fuels are the fuels that are formed naturally from the dead remains of living organisms in millions of years. They include natural gas, petroleum and coal.

Hydrogen is not a fossil fuel because it is not formed by a natural process.

Page No 74:

Question 10:

Which of these is obtained by destructive distillation of coal?
(a) LPG
(b) coal gas
(c) CNG
(d) methane

Answer:

(b) Coal gas
In destructive distillation of coal, coal is heated at high temperature in the absence of air to produce coal tar, coal gas, coke and liquor ammonia as its main by-products.

Page No 74:

Question 1:

Are natural resources living, non-living or both?

Answer:

Natural resources are both living and non-living.
Natural resources refers to resources that are present in our nature, gifted by God and can be freely used, for example, soil, air, sunlight, water, plants, animals etc.

Page No 74:

Question 2:

Petroleum is a renewable resource, as it is naturally renewed in a million years. True or false?

Answer:

True. Although petroleum is a renewable resource, its regeneration takes millions of years. Its rate of depletion is much higher than its rate of formation. As we have limited sources of petroleum, we should use it judiciously.

Page No 74:

Question 3:

The process of conversion of wood into coal is called __________

Answer:

The process of conversion of wood into coal is called carbonisation.

Page No 74:

Question 4:

__________ is the variety of coal with maximum carbon content.

Answer:

Anthracite is the variety of coal with maximum carbon content.



Page No 75:

Question 1:

How is destructive distillation of coal carried out? What are the products obtained and their main uses?

Answer:

Destructive distillation of coal is carried out by heating coal strongly to 1000°C in the absence of air. When coal is heated without air, it does not burn but breaks down to produce following by-products:

(a) Coke: It is used in industries for manufacturing of steel and extraction of many metals. It is used as a domestic fuel for cooking and heating.

(b) Coal tar: It can be used to make soap, fats, dyes, plastics perfumes, drugs, pesticides, explosives etc.

(c) Coal gas: It is used as fuel in coal processing plants and in various other industrial units situated near coal processing plants.

(d) Ammonia: It is used for making nitrogenous fertilisers.

Page No 75:

Question 2:

How is refining of petroleum carried out? Name the important products obtained.

Answer:

Refining of petroleum is carried out by fractional distillation of crude oil.



Process of fractional distillation of crude oil is as follows:

  • Crude petroleum is heated and converted into gas.
  • The gases enter the bottom of a long column (fractional distillation column), which is filled with trays or plates.
  • The gases rise in the column, and gets cooled and condenses when they reach their boiling points
  • The trays collect various liquid fractions which may pass to the condensers, which cool them further and go to the storage tanks.
  • The small chains, usually gaseous molecules, come out at the top, while the liquid medium chain molecules come out at the middle and the solid remains at the bottom.
Important products obtained are kerosene, petrol, diesel, bitumen, LPG( liquefied petroleum gas), paraffin wax, lubricating oil and asphalt.

Page No 75:

Question 3:

List five things that you can do to help in preventing an energy crisis.

Answer:

Following ways and measures can help in preventing an energy crisis:

  1. Vehicles should be driven at constant and moderate speed.
  2. Engines should be switched off at traffic lights and other temporary halts.
  3. Vehicle pooling can reduce number of vehicles plying on road, which, in turn, will lead to less consumption of fuel.
  4. At home, gas stoves should be cleaned properly and burners should not be left burning unnecessarily.

Page No 75:

Question 4:

How is CNG obtained? What are its main uses?

Answer:

CNG is obtained from the deposits of natural gas close to the earth’s surface (usually dwarfed by nearby oil deposits). Deeper deposits formed at higher temperatures and under more pressure have more natural gas than oil. Once the natural gas reserve is discovered, it is extracted from the ground by a pipeline and sent to power plants, factories and processing plants. Here, it is cleaned, separated and converted into CNG (by storing under high pressure), a usable fuel for homes and businesses.

Uses  of CNG:
1. It is very easy to transport through pipes and cylinders.
2. It does not cause pollution on usage, while other petrochemicals like petrol and diesel do.
3. It can be directly used in homes and factories for cooking and other purposes.

Page No 75:

Question 5:

Petroleum and natural gas were formed dead __________

Answer:

Petroleum and natural gas were formed from dead remains of living organisms

Page No 75:

Question 6:

In fractional distillation, hydrocarbons with the __________ (highest/lowest) boiling points condense first.

Answer:

In fractional distillation, hydrocarbons with the lowest boiling points condense first.

Page No 75:

Question 7:

Name two fuels obtained from petroleum, which can be used as domestic fuels.

Answer:

1. LPG: Liquefied petroleum gas is a non-poisonous colourless gas, commonly known as cooking gas. It can be stored in cylinders and is drawn out and used as gas.

2. Kerosene: Kerosene is a flammable pale yellow or colourless oily liquid with a non pleasant odour. It is used as a fuel in lamps and domestic heaters or furnaces.

Page No 75:

Question 8:

Which fuel is used in jet aeroplanes?

Answer:

Kerosene is used as a fuel in jet aeroplanes.
Kerosene is a flammable pale yellow or colourless oily liquid with a unpleasant odour. It is obtained from petroleum.

Page No 75:

Question 9:

Name one non-polluting fuel for vehicles.

Answer:

Compressed Natural Gas (CNG) is a non-polluting fuel for vehicles. Burning of natural gas produces nitrogen oxides, sulphur dioxides, carbon dioxide and carbon monoxide in very small amounts. Thus, it does not cause pollution.

Page No 75:

Question 10:

What is the colour of the crude oil pumped out from a well?

Answer:

Petroleum, also called crude oil, is a thick dark coloured oily liquid. Most of the chemicals present in crude oil are slightly colourless or yellow except bitumen, which brings dark color to crude oil.  

Page No 75:

Question 11:

Which petroleum product is used for surfacing roads?

Answer:

Bitumen is an oil-based substance and is used for surfacing roads. It is a semi solid product obtained from the refining of petroleum.

Page No 75:

Question 12:

Name the petroleum product used to manufacture candles, vaseline, grease, polish, etc.

Answer:

Paraffin wax, a white or colourless soft solid extracted from petroleum, is used to manufacture candles, vaseline, grease and polish.

Page No 75:

Question 13:

Which is the ultimate source of the energy of fossil fuels?

Answer:

Solar energy is the ultimate source of the energy for fossil fuels.
Plants absorb sun's energy through photosynthesis when they are alive and the animals that eat them, get the energy from plants. This energy stays trapped in them for millions of years and gets converted into fuel. Thus, the energy released when fuel is burnt, originally comes from the sun.

Page No 75:

Question 14:

The fuel obtained from coal that is almost pure form of carbon is __________

Answer:

The fuel obtained from coal that is almost pure form of carbon is coke.

Coke is a fuel with high carbon content and few impurities. It is made from destructive distillation of coal.

Page No 75:

Question 1:

Differentiate between renewable and non-renewable resources, giving two examples of each.

Answer:

Renewable resources Non-renewable resources
Resources that are present in infinite amounts (for example, the sun, wind) and can be replaced or reproduced within a reasonable time (for example, wood because we can plant trees) are called renewable resources Resources that are present in a finite amount and cannot be replaced or reproduced within a reasonable time are called non-renewable resources. For example, fossil fuels and minerals which take millions of years to form and cannot be formed artificially.
They can last for ever with limited use. They will finally get exhausted.
They are both living (like forest) and non-living (like water). They are non-living (like coal, petroleum) resources.

Page No 75:

Question 2:

What are fossil fuels?

Answer:

Fuels that are formed from the dead remains of living organisms by natural processes are called fossil fuels. They take millions of years to form.
Petroleum, coal and natural gas are fossil fuels, which are formed after dead remains of living organisms get buried under the sea and earth through natural processes like compression.

Page No 75:

Question 3:

Why should fossil fuels not be wasted?

Answer:

Fossil fuels such as coal, petroleum and natural gas take millions of years to form naturally. They cannot be replaced as fast as they are being consumed. Moreover, it is not possible to make new fossil fuels artificially. If they are overused, they will get exhausted as they are available in nature in limited amount. That is why, they should not be wasted.

Page No 75:

Question 4:

How is coke obtained?

Answer:

Coke is a hard porous black substance which is obtained by destructive distillation of coal.

Page No 75:

Question 5:

What are the advantages of using natural gas as a fuel?

Answer:

Following are the advantages of using natural gas as a fuel:
1. It is easy to transport through pipes and cylinders.
2. It does not cause pollution on usage.
3. It can be directly burnt in homes and factories for cooking and other purposes.

Page No 75:

Question 6:

Why is there a rapid increase in our energy consumption?

Answer:

There is a rapid increase in our energy consumption because of the following reasons:

  1. World’s population is increasing, which means energy requirements are also increasing. People need more energy to cook food, to heat their homes etc., which means more energy is being used.
  2. With the development of countries, energy consumption also increases because people use more devices which need energy, both for functioning and manufacturing.

Page No 75:

Question 7:

Why are fossil fuels our most important source of energy today?

Answer:

Matter that stores energy is called fuel. 
We depend most on fossil fuels for many energy uses because fossil fuels can be burnt, shipped and stored. The energy from fossil fuels is both concentrated and portable. Fossil fuel releases tremendous amount of energy on burning. Natural gas provides cleaner burning and coal is available in abundance.

Page No 75:

Question 8:

What is the main purpose of petroleum refining?

Answer:

Petroleum or crude oil is a complex mixture of organic liquids. Crude oil is of little use in industrial applications.
Petroleum refining is done to convert crude oil into more useful products such as petrol, kerosene, LPG, diesel, waxes, asphalt etc.

Page No 75:

Question 1:

If a resource is renewable, it can still get exhausted. Discuss with two examples.

Answer:

A renewable resource is any resource that can "renew" itself within a person's life span. But most renewable resources become exhaustible if we use them faster than they are renewed or replaced by nature.

Examples:
Ground water is a renewable resource. In recent years, there is a decline in its level because its usage is faster than its replacement. This has led to the drying of wells.

Forests or trees are being cut down to fulfil our need of wood for furniture, paper etc. It usually takes 25 years or more for a tree to grow to its original state. If new trees do not grow up and replace the older trees as fast as the older trees are cut down, sooner or later they would be exhausted.  

Page No 75:

Question 2:

Why is topsoil considered a non-renewable resource even though it is constantly being formed by weathering of rocks?

Answer:

Topsoil is considered a non-renewable resource because its rate of erosion is faster than its rate of regeneration. Although topsoil does build up over time through weathering of rocks and minerals and decaying of organic matter, it does not build up to an appreciable amount in a person's lifetime.

Page No 75:

Question 3:

Why do we feel the need for conservation more today than our ancestors did?

Answer:

Our ancestors had modest energy requirements, mostly for cooking, lighting and heating. In today's society, energy consumption by humans has increased manyfold as compared to energy consumed by early humans because people have progressed. Developed nations use more energy especially for transportation and industry. Most of the energy we use today comes from fossil fuels which are non-renewable on a human time scale.
That is why, there is more need for energy conversation today than early times.

Page No 75:

Question 4:

How was coal formed?

Answer:

Coal was formed by the dead remains of the plants by the process of carbonisation. Millions of years ago, dead flora and fauna in forests got buried under soil, rocks and other land masses due to earthquakes, volcanic eruptions and floods. With the passage of time, more soil layers got deposited on it and they were compressed and went deeper and deeper beneath the earth. This raised the temperature and pressure beneath the soil. This initiated the process of burning these dead remains. Slowly, all the vegetation got converted into coal, which is a rich form of carbon.

Page No 75:

Question 5:

What are the important uses of coke?

Answer:

Uses of coke:

  1. It is used in industries for manufacturing of steel and for the extraction of many metals.
  2. It is used in thermal power plants to produce electricity.
  3. It is used as a domestic fuel for cooking and heating.
 

Page No 75:

Question 6:

How was petroleum formed?

Answer:

Petroleum was formed by the dead remains of the sea animals which got trapped under soil and clay and more deposits were formed with time. Due to depth, the temperature and pressure raised and over the years, they got converted into petroleum oil. Since, oil is lighter than water, it did not mix with water and arose to the superficial rocks, which did not allow it to pass through them.

Page No 75:

Question 7:

Name four important products of petroleum and give their uses.

Answer:

Various constituents of petroleum oil obtained during fractional distillation in oil refineries are:

  1. Liquid Petroleum Gas (LPG): It is primarily used as domestic fuel. Now, it is also used as fuel in vehicles and industry because it is less polluting and easy to transport.
  2. Petrol: It is a black liquid used as fuel in light vehicles like scooters, cars, etc. It is also used as aviation fuel and for dry cleaning of fabrics.  
  3. Kerosene: It is used as fuel in stoves, lamps and jet aircrafts.
  4. Diesel: It is used as fuel for heavy vehicles and electric generators. 

Page No 75:

Question 8:

What are the advantages of using energy judiciously?

Answer:

Advantages of judicious use of energy:

  1. Fossil fuels are primary source of energy today. If they are used indiscriminately, they will be exhausted because they are available in limited amount. It takes millions of years to form fossil fuels and it is not possible to make new fossil fuels artificially. Therefore, they should be wisely used and not wasted.
  2. Judicious use of energy today will help future generations to use the available resources.



Page No 76:

Question 1:

If a resource can be replaced within ten years by natural processes, would you classify it as renewable or non-renewable?

Answer:

If a resource can be replaced within ten years by natural processes, it can be classified as renewable. Renewable resource is a resource that can renew itself within a person's life span, while a non-renewable resource takes millions of years to form.

Page No 76:

Question 2:

All renewable resources are inexhaustible. Do you agree? Give reasons.

Answer:

Renewable resources are resources that are present in infinite amounts (for example, the sun, wind) and can be replaced or reproduced at a scale comparable to its consumption (for example, wood because we can plant trees).

All renewable resources are inexhaustible, i.e., last forever with limited use.
But most renewable resources become exhaustible if we use them faster than they are renewed or replaced by nature.

Page No 76:

Question 3:

All combustible substances are not fuels. Why?

Answer:

Fuel is a substance which on burning releases a large amount of energy as heat at a reasonable cost and leaves behind little ash content. For example, coal, natural gas, petroleum nearly meet all these conditions.
Combustible substance is the one which liberates heat on burning. The amount of heat liberated is different for different substances. This determines whether or not a substance is a good fuel.
All the combustible substances are not fuels because many of them produce less amount of heat for a particular amount of energy input on burning and leave behind high ash content; for example, paper, cloth, etc. 

Page No 76:

Question 4:

Can fossil fuels be made in the laboratory?

Answer:

Fossil fuels can’t be prepared in our laboratory because it took millions of years for dead bodies of plants and animals to get converted into fossil fuels. Moreover, necessary conditions of high temperature and pressure for the conversion of dead bodies into fossil fuel cannot be created in a laboratory.

Page No 76:

Question 5:

Conservation of resources means avoiding their wasteful use. Does this definition cover all aspects of conservation? Explain.

Answer:

Conservation of resources means not only avoiding their wasteful use but also maintaining their quality. It can also be defined as restoring, protecting and maintaining the natural ecosystem, vegetation and wildlife.

Page No 76:

Question 6:

In a petroleum well, crude oil is found above water. Which two properties of petroleum make it possible to form a layer of it above water?

Answer:

Following two properties of petroleum make it possible to form a layer of it above water:

  1. Petroleum is immiscible with water, i.e., it cannot be mixed with water. 
  2. Petroleum oil is lighter than water, it forms a layer above water.



View NCERT Solutions for all chapters of Class 8