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

Get here the accurate and comprehensive NCERT Solutions for Class 8 Science Chapter 6 - Combustion and Flame. All the solutions are available for download in PDF format.

Created On: Jun 17, 2021 22:56 IST
NCERT Solutions for Class 8 Science Chapter 6 - Combustion and Flame
NCERT Solutions for Class 8 Science Chapter 6 - Combustion and Flame

NCERT Solutions for Class 8 Science Chapter 6 - Combustion and Flame are best to understand the concepts clearly and learn the answer writing skills for obtaining high scores in exams. These NCERT Solutions have been created by the subject matter experts. Moreover, these solutions have been prepared only for the latest NCERT Class 8 Science Book hence are best for the exam preparations in the current academic session 2021-2022.

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

Exercise

1. List conditions under which combustion can take place.

Answer:

There are three conditions required for combustion to take place. These are:

(i) Presence of a fuel

(ii) Presence of air (or oxygen)

(iii) Ignition temperature

2. 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 _________.

Answer:

(a) Burning of wood and coal causes pollution of air.
(b) A liquid fuel used in homes is LPG.
(c) Fuel must be heated to its ignition temperature before it starts burning.
(d) Fire produced by oil cannot be controlled by water.

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

Answer:

CNG produces the harmful products like carbon dioxide gas, carbon monoxide gas, sulphur dioxide and nitrogen dioxide in very small amounts. Whereas petroleum releases these pollutants in very large quantities. Thus CNG is comparatively a cleaner fuel. That is why the use of CNG in automobiles has reduced pollution in our cities

4. Compare LPG and wood as fuels.

Answer:

LPG

Wood

1. It has high calorific value about 55000 kJ/kg.

1.It has low calorific value about 17000 to 22000 kJ/kg.

2. It is a smokeless fuel.

2. It produces a lot of smoke.

3. It does not cause any environmental pollution.

3. It releases unburnt carbon particles which are dangerous pollutants and cause respiratory diseases, such as asthma.

3. It is a liquid fuel.

3. It is a solid fuel.

4. It does not leave any residues after burning.

4. It leaves behind ashes that pollute air and water.

5. It has low ignition temperature.

6. It has high ignition temperature

5. 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:

(a) Since water is a conductor of electricity, it can easily conduct electric current and cause electric shock  to the person trying to extinguish fire. Therefore, water is not used to control fires involving electrical equipment.

(b) LPG is a better domestic fuel than wood because as it does not produce smoke and other pollutants like unburnt carbon particles, which cause respiratory issues.

(c) Paper by itself catches fire easily because it has low ignition temperature but when wrapped around an aluminium pipe then the heat given to it gets absorbed by the aluminium pipe and the piece of paper does not get its ignition temperature. Therefore, it does not catch fire.

6. Make a labelled diagram of a candle flame.

Answer:

Labelled diagram of a candle flame is given below:

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

Answer:

The calorific value of a fuel is expressed in kilojoules per kilogram (kJ/kg).

8. Explain how CO2 is able to control fires.

Answer:

Carbon dioxide (CO2) being heavier than oxygen, covers the fire like a blanket. Since the contact between the fuel and oxygen is cut off, the fire is controlled.

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

Answer:

Green leaves contain a lot of moisture in them due to which they have a high ignition temperature. Thus, they do not catch fire easily. Whereas, dry leaves have no moisture in them hence they have low ignition temperature. Therefore, they catch fire easily.

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

Answer:

A goldsmith uses the outermost zone of the candle flame for melting gold and silver because this zone has the highest temperature which helps to melt the metals easily.

11. 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.

Answer:

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

Now, heat produced by complete combustion of 4.5 kg of fuel = 180000 kJ

Thus, heat produced by complete combustion of 1Kg of fuel = 180000/4.5 = 1KJ/Kg
= 40,000 kJ/kg

Hence, the calorific value of the fuel is 40,000 kJ/kg.

12. Can the process of rusting be called combustion? Discuss.

Answer:

Combustion is a rapid chemical reaction of an inflammable substance with oxygen to give heat and light On the other hand, in rusting, metal reacts with oxygen slowly to form metal oxide and gives out a very small amount of heat. Thus, rusting may be considered slow combustion.

13. 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?

Answer:

The water in Ramesh's beaker will heat up in a shorter time because he kept his beaker in the outermost zone of the flame that has the highest temperature.

All these solutions can also be saved in PDF from the following link:

Download NCERT Solutions for Class 8 Science Chapter 6 in PDF

Also check the NCERT Books and NCERT Solutions for all major subjects of Class 8:

NCERT Books for All Subjects of Class 8 (Latest Editions for 2021-2022)

NCERT Solutions for All Subjects of Class 8 (Updated for 2021-2022)                                                                                                           

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