NCERT Solutions for Class 8 Science Chapter 6 Combustion and Flame


Do you know why blue flame is used to melt gold?

What is the correlation between acid rain and fuel-burning?

These are some of the interesting facts that you will learn in this chapter on combustion and flame of Class 8 Science NCERT Solutions. You will learn the definition and types of combustion, the different types of fuel and their uses as well as some bad environmental effects of burning fuel. Other important definitions include ignition temperature, flammable and non-flammable substances and practical ways to put out a fire.

Download PDF of NCERT Solutions for Class 8 Science Chapter 6

Question 1 - List conditions under which combustion can take place.

Answer 1 - The following are the conditions that must be met for combustion to happen:

1. Oxygen

2. Temperature of ignition (the minimum temperature at which a substance catches fire).


3. The presence of a fuel


Question 2 - Fill in the blanks.

(a) Burning of wood and coal causes _________ air. (polluted)

(b) A liquid fuel, used in homes is ________ (liquefied petroleum gas)

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

(d) Fire produced by oil cannot be controlled by _______ (water)


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

Answer 3 - CNG is also known as compressed natural gas. It’s another name for CNG.

CNG, which is pollution-free, may be utilized in automobiles since it has a low ignition temperature and complete combustion.

CNG can be used to minimize pollution since, unlike other fuels, it burns fully cleanly and emits very few hazardous gases.


Question 4 - Compare LPG and wood as fuels.

LPG

Fuel

It burns cleanly and leaves no trace.

It produces ash as a byproduct of combustion.

It pollutes the environment less.

It contributes to increased pollution.

It's simple to store.

It necessitates a large amount of area.


Question 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 aluminum pipe does not.

Answer –

a) Water is an electrical conductor; it may easily conduct electric current and cause electric shocks or short-circuits. As a result, water cannot be used to put out a fire caused by electrical equipment.

b) LPG is a better household fuel since it does not emit smoke or carbon particles which can cause respiratory issues. However, wood emits a lot of unburnt carbon particles, which can cause respiratory issues.

c) A paper that is wrapped around an aluminium pipe catches fire readily because it has a low ignition temperature, but the temperature is lowered because the aluminium metal absorbs the heat that is provided to the paper. As a result, it does not catch fire.

Question 6 - Make a labeled diagram of a candle flame.

Answer 6 -

Diagram of candle flame

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

Answer - kJ/kg


Question 8 - Explain how CO2 is able to control fires?

Answer - It is heavier than oxygen and acts as a blanket over the flames. By displacing oxygen, it prevents oxygen from contacting the fuel.

Carbon dioxide is maintained in liquid form in cylinders. Carbon dioxide expands tremendously as it is discharged from the cylinder. Because of the lack of oxygen and the ice-cold temperature of the Carbon dioxide when released from the extinguisher, this is an effective approach to put out fires and also prevent them from returning.


Also get access to
NCERT Solutions for Class 8 Maths
Class 8 Maths Worksheets
Class 8 Maths Notes

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

Answer 9 - It's difficult to light a mound of green leaves on fire, but dried leaves burn quickly. Green leaves contain a lot of moisture, which prevents them from reaching their ignition temperature, making them tough to light. Because dry leaves do not contain water, they readily heat up to their ignition temperature and catch fire.


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

Answer 10 - The non-luminous outermost zone of a flame is used by a jeweler to melt gold and silver because it is the hottest zone of the flame and has the highest temperature.


Question 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 11 - Calorific value of a fuel = Heat Produced / Amount of fuel = 1800004.5 kJ/kg = 40,000 kJ/kg.


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

Answer 12 - During the formation of its oxide, the rusting process produces heat. As a result, we can consider the rusting process a combustion process.


Question 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 13 - Since Ramesh placed the water closer to the hottest zone of the flame, it will heat up in a shorter amount of time.




Links to Other Resources for Class 8 Science
Other Class 8 Science Related Links
Understanding Structure and Functions of a Cell
Deforestation, Afforestation and Reforestation
Frictional Force Definition, and Types with Example
Formation and Uses of Coal and Petroleum
Water Pollution Causes and Effects with Example