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Important Questions for CBSE Class 8 Science Chapter 6 - Combustion and Flame

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Last updated date: 23rd May 2024
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CBSE Class 8 Science Chapter-6 Important Questions - Free PDF Download

CBSE Class 8 Science Chapter 6 - Combustion and Flame is a crucial part of the syllabus of this subject. Students learn the different types of combustion reactions and flames here. To understand these concepts well and to use them for framing the right answers, download and solve the Class 8 Science Chapter 6 - Combustion and Flame Important Questions. Compare your answers to the solutions given for these questions and take your preparation to the next level. Develop your concepts and knowledge by practising solving these questions to score more in the exams.


Significance of CBSE Class 8 Science Chapter 6 - Combustion and Flame Important Questions

Combustion is a type of chemical reaction. We generally interpret it as burning but there is much more to its concepts. Chapter 6 of the Class 8 Science syllabus is all about what combustion is and how many types of combustion are there. This chapter explains the different types of combustion by using proper examples. Hence, students will learn the fundamental concepts of combustion and flames in this chapter and will proceed to solve the exercises.


Once the exercises are solved, students will need the right platform to assess their preparation level. They download and solve the Class 8 Science Chapter 6 Important Questions developed by the subject experts of Vedantu. These questions have been framed by following the CBSE Class 8 Science level so that students can easily comprehend their contexts and can frame the right answers. Hence, solving these questions will automatically escalate the knowledge foundation of the students.


Advantages of CBSE Class 8 Science Chapter 6 - Combustion and Flame Important Questions

  • The questions are set in such a way that you will have to have a good grip on all the scientific concepts taught in this chapter. It means you can easily judge your preparation level by comparing your answers to the solutions to do the needful.

  • Focus on the answering formats used to compile the solutions. Learn how to do the same by practising solving these questions to score more in the exams.

  • Resolve doubts related to important questions by using specific solutions. Leave no queries back and take a step ahead to complete preparing this chapter perfectly.

Important questions for Class 8 Science Chapter 6 combustion and flames with solutions have been created by subject experts at Vedantu. All the chapters of Class 8 important questions are available on Vedantu in the form of PDF. Subjects like Science, Maths, English will become easy to study if you have access to NCERT Solution for Class 8 Science, Maths solutions, and solutions of other subjects. You can also download NCERT Solutions for Class 8 Maths to help you to revise the complete syllabus and score more marks in your examinations.

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Study Important Questions for Class 8 Science Chapter 6 – Combustion and Flames

Very Short Answer Questions: (1 Marks)

1. ________ do not produce flames but generate heat. 

A. Kerosene

B. Oil

C. Petrol

D. Coal

Ans: D. Coal


2.  Which of the following is the product of combustion? 

A. Carbon dioxide and water

B. Oxygen and Water 

C. Only Carbon Dioxide

D. Only Oxygen

Ans: A. Carbon Dioxide and Water


3. Which one of the following is a combustible substance? 

A. Wood

B. Nail

C. Steel spoon

D. All of These

Ans: A. Wood


4. __________ is produced when a charcoal is burnt in a closed room? 

A. carbon dioxide

B. Nitrogen Dioxide 

C. Carbon Monoxide

D. All of These

Ans: C. Carbon Monoxide


5. What is used as fuel to run automobiles? 

A. Petrol

B. Diesel

C. Kerosene

D. Both A and B

Ans: D. Both A and B


6. A good fuel is one which is ______________. 

A. Cheap

B. Readily Available 

C. Produces Large Amount of Heat

D. All of These

Ans: D. All of these


7. How many zones are there in the flame? 

A. One

B. Three

C. Two

D. Four

Ans: B. Three


8. What are the requirements essential for producing fire?

Ans: Requirements for producing fire:

  • Fuel

  • Air (Oxygen)

  • Ignition Temperature


9. Charcoal burns in air to produce ______________, _______________ and ___________.

Ans: Carbon Dioxide, Heat and Light.


10. Name any one chemical substance which helps to put off the fire other than carbon dioxide.

Ans: Bicarbonates of sodium or potassium will help us to put off the fire.


11. In the Sun, heat and light are produced by ___________.

Ans: Nuclear Reaction.


12. Expand LPG.

Ans: Liquified Petroleum Gas


13. The lowest temperature at which a substance catches fire is called ___________.

Ans: Ignition Temperature


14. The unit of a calorific value of a fuel is _________________.

Ans: Kilojoules per Kilogram.


Short Answer Questions: (3 Marks)

15. Classify the following into combustible and non-combustible substances. 

iron rod, wood, steel spoon, stone, newspaper, petrol

Ans:

Combustible

Non-Combustible

Wood, Newspaper, Petrol

Iron rod, Steel rod, Stone


16. Kerosene oil while burying gives flames on the other hand charcoal does not produce flames? Give a reason.

Ans: Only substances which vaporise during burning can produce flames such as kerosene whereas charcoal doesn’t vaporise when starting burning. Thus, charcoal doesn’t produce any flame.


17. If a fire breaks out in the petrol station, how does a fire extinguisher help to put off the fire?

Ans: A combination of liquid and gaseous carbon is used in fire extinguishers. Because carbon dioxide is heavier than oxygen, it blankets the fire. Thus, the fire is controlled because there is no contact between the fuel and the oxygen.


18. Petrol can be considered as a good fuel. Why?

Ans: Reasons petrol is considered a good fuel:

a. It is affordable.

b. It is easily available.

c. It has a high calorific value.

d. It is easy to transport.

e. It burns easily and produces more heat.


19. What will happen when a paper cup with water is heated?

Ans: When we heat a paper cup containing water, the water will absorb the heat of the flame. Hence, the ignition temperature of paper will not reach and it will not start burning easily.


20. Give four examples of inflammable substances.

Ans: Four inflammable substances:

a. Kerosene

b. Petrol

c. LPG

d. Diesel

 

21. How does combustion start in a matchstick?

Ans: Antimony trisulphide and potassium chlorate are found in the matchstick's head. The rubbing surface has powdered glass & red phosphorus. Red phosphorus is transformed to white phosphorus when the match is hit against the rubbing surface. This combines with the potassium chlorate in the matchstick head to provide enough heat to ignite antimony trisulphide and start the combustion process.


22. Define the following. 

a. Combustion: Combustion is a chemical reaction in which a material combines with oxygen present in air to produce heat.

b. Fuel: Fuels are the substances which undergo combustion.

c. Calorific Value: The calorific value of a fuel is the quantity of heat energy produced when 1 kg of fuel is completely burned.


23. Why is it not advised to use water if an electrical equipment is on fire?

Ans: Water is a good conductor of electricity which increases the risk to the helpers. Therefore it is advised not to use water if there is any electrical equipment on fire.


24. Label the different zones of a candle flame.


Candle Flame


Ans: 

A – outer zone of complete combustion (Blue coloured) 

B – Middle zone of partial combustion (yellow coloured) 

C – Innermost zone of unburnt wax vapours (black coloured)


25. In an experiment, 1 kg of fuel was completely burnt. The heat produced was measured to be 9,000 kJ. 

a. What will be the head produced for 7 kg of fuel?

Ans: If the heat produced for 1 kg of fuel is 9000 kJ. 

Then heat produced for 7 kg is = 7 X 9000 

         = 63,000 kJ

b. Calculate the calorific value of the fuel.

Ans: Calorific value of the fuel = Amount of heat energy produced / weight of fuel burnt 

        = 63000/8 kJ/kg 

        = 9,000 kJ/kg


Long Answer Questions: (5 Marks)

26. List the characteristics of an ideal fuel.

Ans: Characteristics of an ideal fuel:

a. It should be affordable.

b. It should be easily available.

c. It should have high calorific value.

d. It should be easy to transport.

e. It should burn easily and produce more heat.

f. It should not leave any unwanted residue behind on burning.

g. It should be more environmentally friendly.


27. With the help of an experiment show that air is necessary for combustion.

Ans: 

i. Take two lighted candles on a table. 

ii. Put a glass chimney over one candle s in such a way that air can enter the chimney. 

iii. On the other hand, put a chimney over another candle and place a glass plate over the chimney. 

iv. We observe that the first candle continues to burn whereas flame in the second candle extinguishes. 


This is because the air supply was cut off after placing the glass plate over the chimney and the candle was not able to burn in the absence of air. This shows that air (oxygen) is necessary for combustion.


28. Explain the different types of combustion with examples.

Ans: There are three different types of combustions:

a. Rapid Combustion: It's a form of combustion in which a substance burns quickly, releasing heat and light. Example: LPG.

b. Spontaneous Combustion: The sort of combustion in which a substance spontaneously erupts into flames without any apparent cause. 

Example: Phosphorus. It burns in air at ambient temperature without igniting.

c. Explosion: When a substance is ignited, it undergoes a rapid reaction that produces heat, light, and sound. The reaction produces a significant amount of gas and heat, which is then released. This type of combustion is called an explosion.

Example: Bursting of firecrackers.


29. Explain in detail the harmful effect caused by burning of fuel.

Ans: Harmful effects of burning of fuels:

a. The carbon based wood, coal etc leaves unburnt substances which causes air pollution. They can be harmful for humans too, causing respiratory diseases.

b. Most of the fuel releases carbon dioxide on burning. This process slowly increases carbon content in the atmosphere leading to bigger problems like global warming.

c. Incomplete combustion of fuel can produce carbon monoxide instead of dioxide which when inhaled can rapidly combine with our blood and work as poison.

d. In a few cases sulphur dioxide is produced on burning of fuel which is harmful to both humans and the environment.


Download Class 8 Science Chapter 6 Important Questions PDF

Important questions will help the students in ways that they should not struggle to prioritize the topics while their exam preparation. Class 8 Science Chapter 6 important questions are created following the recent CBSE guidelines.

Topics covered in the Class 8 Science Chapter 6 are materials combustion and flame, what is combustion? How do we control fire? Types of combustion, flame, the structure of a flame, What is fuel? Fuel efficiency, etc.


Chapter 6 - Combustion and Flames

  • Combustion

It is a type of chemical process, in which a substance reacts with oxygen to produce heat and light is called combustion. One example of combustion is the burning of wood. There are two types of substances mainly combustible substances and non-combustible substances. Substances that easily catch fire are known as combustible substances, some of the examples of combustible substances are paper, coal, and wood. The substances which do not catch fire readily are known as incombustible substances, some of the examples are sand, water, and glass.

There are two types of combustion mainly rapid combustion and spontaneous combustion. When something burns rapidly and produces heat and light like LPG gas is known as rapid combustion.

And when something bursts into flames without application of any other thing is known as spontaneous combustion. The spontaneous reaction can be seen, when phosphorus is in direct contact with air at room temperature.


  • Flame

It is the visible and gaseous part of the fire, the flame is the light energy released during the process of combustion. There are different zones of flames, the outer zone is of complete combustion, the middle zone is of partial combustion, the innermost zone is of uncombusted substance.

Smoke is an example of solid unburnt particles, which disappears in the gas. Smoke is of black colour due to the presence of unburnt carbon particles in the smoke. Fire can be controlled by removing all the factors of the combustion like fuel, oxygen, and by lowering the ignition temperature. A fire extinguisher is a device that is used to control the fire, by cutting off the supply of oxygen or by bringing down the temperature of the fuel.


Download CBSE Class 8 Science Chapter 6 - Combustion and Flame Important Questions PDF

Get the free PDF version of these important questions and answers. Solve these questions at your convenience at home and use them as a mock test tool. Focus on how the experts have solved these questions and learn to use the scientific concepts of this chapter well. Sharpen your answering skills by following the answers given in the solutions and stay ahead of the competition.

Conclusion 

The compilation of important questions for CBSE Class 8 Science Chapter 6, "Combustion and Flame," plays a pivotal role in the educational journey of students. These questions serve as invaluable aids for a comprehensive understanding of the subject. They offer a structured approach to learning, highlighting key concepts related to combustion, types of flames, and fire safety measures. As an integral part of exam preparation, these questions help students identify and focus on the most critical topics, ensuring readiness for assessments. By engaging with these questions, students not only consolidate their knowledge but also hone critical thinking skills. In essence, important questions facilitate a deeper exploration of combustion and flame, contributing to enhanced understanding and academic excellence.

FAQs on Important Questions for CBSE Class 8 Science Chapter 6 - Combustion and Flame

Q1. It is observed at petrol pumps and airports that hydrocarbon fire extinguishers are used, instead of soda-acid fire extinguishers. Why do you think so?

There are more chances of fire breaking out at petrol pumps and airports due to oil. In these kinds of situations, soda-acid fire extinguishers do not work. It's because it has water which extinguishes the fire by cooling down the place. Fire does not get controlled as water sinks to the bottom because it is heavier than oil. That is why, hydrocarbon fire extinguisher should be used as it is very useful because it contains turkey red oil. It causes the foaming of carbon dioxide gas under pressure. The surface of the burning substances is covered by foam and dispels the supply of air to control fire.

Q2. What are the reasons for forest fires?

Forest fires occur due to the following reasons. When lightning strikes the forest trees or areas, it may lead to forest fires. Dry grass catches fire at some places during the extreme heat of summer. Very soon, the fire from the grass will spread to the whole forest. Another reason for forest fires can be due to the sparks from rock falls in a mountainous region. Human causes or activities can lead to forest fires. Volcanic eruption is also one of the reasons.

Q3. Why is LPG a better domestic fuel than wood?

Wood was used both as a domestic and industrial fuel for centuries. However, coal and other fuels like LPG have replaced wood. LPG has much higher calorific value compared to wood. So, on burning, LPG produces much more heat than an equal mass of wood. A lot of smoke is produced when the wood is burnt which is harmful for humans whereas LPG burns without producing any smoke. A lot of ash is left on burning of wood whereas no solid residue is left behind when LPG is burned completely. LPG is a cleaner fuel than wood as it does not cause environmental problems. However, for wood, we need to cut trees which will lead to deforestation which is quite harmful to the environment.

Q4. What do you mean by fuel and efficiency of fuel?

To produce heat, materials that are burnt are known as fuel. Examples such as wood, coal, LPG, kerosene, petrol, and diesel are all fuels. Different amounts of heat are produced on the burning of different fuels. On complete burning of one kilogram of fuel, the amount of heat produced by it is known as the Calorific value. The calorific value of a fuel is expressed in the form of a unit of kilojoule per kilogram. To learn more about the topic, refer to the Important Questions for CBSE Chapter 6 - Combustion and Flame of Class 8 Science  provided by Vedantu. These are available on both the website and the App free of cost.

Q5. “When the oxygen supply is sufficient, then the fuels burn completely producing mainly blue flame”. Why?

A blue flame is said to be a non-luminous flame as it does not produce much light.  When the “complete combustion” of fuel takes place, the blue flame is produced. For example, in the kitchen gas stove, complete combustion of LPG takes place. The LPG burns with a blue flame in the LPG stove. The burner of the kitchen gas stove is designed in such a way that it helps to provide sufficient air for the complete combustion of LPG.