NCERT Solutions - Science , Class 8 solutions for Chapter 6 Combustion and Flame

List conditions under which combustion can take place.

Fill in the blanks.

(a) A place where animals are protected in their natural habitat is called _________ .

(b) Species found only in a particular area is known as _______ .

(c) Migratory birds fly to faraway places because of __________ changes.

Q1) List conditions under which combustion can take place.

A substance which reacts with oxygen giving heat is called a combustible substance. Which, one of the following is a combustible substance?

(a) iron nail

(b) glass

(c) stone piece

(d) wood

Q2) Fill in the blanks.

(a) Burning of wood and coal causes _____________ of air.

(b) A liquid fuel, used in homes is _______________.

(c) Fuel must be heated to its ___________ ___________ before it starts burning.

(d) Fire produced by oil cannot be controlled by ____________ .

Which one of the following has the highest calorific value?

(a) kerosene

(b) biogas

(c) LPG

(d) petrol

Fill in the blanks.

(a) Burning of wood and coal causes __________of air.

(b) A liquid fuel, used in homes is__ .

(c) Fuel must be heated to its ____________ before it starts burning.

(d) The fire produced by oil cannot be controlled by___ .

Explain how the use of CNG in automobiles has reduced pollution in our cities.

Q3) Explain how the use of CNG in automobiles has reduced pollution in our cities.

Magnesium ribbon on burning in air produces

(a) magnesium oxide, water and light

(b) magnesium oxide and heat

(c) magnesium oxide, heat and light

(d) magnesium oxide, water and heat

Which of the following is not a combustible substance?

(a) camphor

(b) glass

(c) straw

(d) alcohol

Q4) Compare LPG and wood as fuels.

Compare LPG and wood as fuels

Give reasons.

(a) Water is not used to control fires involving electrical equipment.

(b) LPG is a better domestic fuel than wood.

(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

Answer in brief.

(a) Why should we conserve biodiversity?

(b) Protected forests are also not completely safe for wild animals. Why?

(c) Some tribals depend on the jungle. How?

(d) What are the causes and consequences of deforestation?

(e) What is Red Data Book?

(f) What do you understand by the term migration?

Q5) Give reasons.

(a) Water is not used to control fires involving electrical equipment.

(b) LPG is a better domestic fuel than wood.

(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

The substance that does not burn with flame is

(a) LPG

(b) camphor

(c) dry grass

(d) charcoal

Q6) Make a labelled diagram of a candle flame.

Make a labelled diagram of a candle flame.

On placing an inverted tumbler over a burning candle, the flame extinguishes after some time. This is

because of the nonavailability of

(a) oxygen

(b) water vapors

(c) carbon dioxide

(d) wax

Q7) Name the unit in which the calorific value of a fuel is expressed.

If a person’s clothes catch fire, the best way to extinguish the fire is to:

(a) throw water on the clothes.

(b) use a fire extinguisher.

(c) cover the person with a woolen blanket.

(d) cover the person with a polythene sheet.

Name the unit in which the calorific value of a fuel is expressed.

The substance expected to have the highest ignition temperature out of the following is

(a) kerosene

(b) petrol

(c) coal

(d) alcohol

Explain how CO2 is able to control fires.

Q8) Explain how $CO_2$ is able to control fires.

It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Choose the correct statement about inflammable substances from the following. They have:

(a) low ignition temperature and cannot catch fire easily.

(b) high ignition temperature and can catch fire easily.

(c) low ignition temperature and can catch fire easily.

(d) high ignition temperature and cannot catch fire easily.

Q9) It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Choose the incorrect statement from the following. Forest fires are usually due to:

(a) carelessness of humans

(b) heat of sun

(c) cutting of trees

(d) lightning strike

Q10) Which zone of a flame does a goldsmith use for melting gold and silver and why?

Which zone of a flame does a goldsmith use for melting gold and silver and why?

In an experiment, 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.

Q11) In an experiment 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.

The calorific value of a fuel is expressed in a unit called

(a) kilojoule per litre

(b) kilogram per mililitre

(c) kilojoule per gram

(d) kilojoule per kilogram

Q12) Can the process of rusting be called combustion? Discuss.

Can the process of rusting be called combustion? Discuss.

In villages, people use wood as fuel because:

(a) it is considered to be an ideal fuel.

(b) of its easy availability and low cost.

(c) it is environment friendly.

(d) it catches fire easily.

Q13) Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?

Which among the following is considered as the cleanest fuel?

(a) cow dung cake

(b) petrol

(c) kerosene

(d) hydrogen gas

Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?

Choose the incorrect statement from the following. A good fuel is one which:

(a) is readily available.

(b) produces a large amount of heat.

(c) leaves behind many undesirable substances.

(d) burns easily in the air at a moderate rate.

Shyam was cooking potato curry on a chulha. To his surprise, he observed that the copper vessel was getting blackened from outside. It may be due to:

(a) proper combustion of fuel.

(b) improper cooking of potato curry.

(c) improper combustion of the fuel.

(d) burning of the copper vessels.

Fill in the blanks in the following sentences.

(a) A ____________ process in which a substance reacts with __________ to give off heat is calledcombustion.

(b) When the clothes of a person catch __________, the person is covered with a __________ toextinguish fire.

(c) The __________ temperature at which a substance catches fire is called its __________ temperature.

(d) The substances which have very ________________ ignition temperature and can easily catch fire with a flame are called __________ substances.

(e) The substances which vapourise during __________, give flame.

Some words (underlined) in the following sentences are jumbled up. Write them in their correct form.

(a) Seldie is a combustible substance.

(b) Slags is a non-combustible material.

(c) Chittsmack does not burn by itself.

(d) Some substances on combustion produce thea and mafel.

(e) The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value.

Two glass jars A and B are filled with carbon dioxide and oxygen gases, respectively. In each jar a lighted candle is placed simultaneously. In which jar will the candle remain lighted for a longer time and why?

Anu wants to boil water quickly in a test tube. On observing the different zones of the flame, she is not able to decide which zone of the flame will be best for boiling water quickly. Help her in this activity.

Why is the use of diesel and petrol as fuels in automobiles being replaced by Compressed Natural Ga (CNG) in big cities?

Boojho wants to separate the following materials as combustible and non-combustible. Can you help him?

Indicate whether the following statements are True or False. Also write the false statements in their correct form.

(a) Air is necessary for combustion.

(b) Magnesium is a non-combustible metal.

(c) Carbon dioxide is an excellent fire extinguisher.

(d) Calorific value of wood is higher than that of coal

Match the items of Column A with the items of Column B

Match the following for the flame of a candle.

If you hold a piece of iron wire with a pair of tongs inside a candle flame or a Bunsen burner flame, what will you observe? Will it produce a flame?

Fill in the blanks using the words given in the box.

(a) A chemical process in which a substance reacts with oxygen to give off heat is called __________.

(b) Wood, paper, CNG are __________ substances.

(c) The lowest temperature at which a substance catches fire is called its __________ temperature.

(d) Ignition temperature of __________ is lower than that of wood.

(e) The substances which have very low __________ temperature and can easily catch fire with a flame are called __________ substances.

(f) The amount of heat energy produced on complete combustion of 1kg of a fuel is called its __________

People usually keep Angethi/burning coal in their closed rooms during the winter season. Why is it advised to keep the door open?

Write True/False against the following statements and also correct the false statement.

(a) A physical process in which a substance reacts with oxygen to give off heat is called combustion.

(b) Water is the best extinguisher for fires involving electrical equipment.

(c) Alcohol, CNG, and LPG are inflammable substances.

(d) The increased concentration of nitrogen in the air is believed to cause global warming.

(e) Greater the calorific value, the better is the fuel.

(f) The Middle zone is the hottest zone of a flame.

(g) The substances which vapourize during burning, give flame.

Cracker on ignition produces sound. Why?

What do you understand by fuel efficiency?

You are provided with three watch glasses containing milk, petrol and mustard oil, respectively.

Suppose you bring a burning candle near these materials one by one, which material(s) will catch fire instantly and why?

Manu was heating oil to fry potato chips. The cooking oil all of a sudden caught fire; he poured water to extinguish the fire. Do you think this action was suitable? If yes, why? If not, why not? In such a condition what should Manu have done?

What are the three essential requirements to produce fire? How fire extinguisher is useful for controlling the fire.

Give two examples each for a solid, liquid and gaseous fuel along with some important uses.

The calorific values of petrol and CNG are 45000 kJ/kg and 50,000 kJ/kg, respectively. If you have a vehicle which can run on petrol as well as CNG, which fuel will you prefer and why?

Although wood has a very high calorific value, we still discourage its use as a fuel. Explain.

Forest fire produces a lot of air pollution. Write in brief about the reasons for forest fires.

Complete the crossword Fig. with the help of the clues

Across

Non-metal which catches fire if exposed to air (10)
The lowest temperature at which a substance catches fire is called its __________ temperature. (8)
The most common fire extinguisher. (5)

Down

A chemical process in which a substance reacts with oxygen to give off heat. (10)
Petrol is used as a __________ in automobiles. (4)
It is as hard as stone and black in color. (4)

Ncert solutions science class 8 Solutions for Chapter 6 combustion and flame