In this post we will see the solution of class 8th , 6 chapter all the solution is prepared by the expert teacher
You can check the Complete Science Solution here – NCERT Class 8th Science Solutions – Complete Solution List
Chapter 6th solution
1. List conditions under which combustion can take place.
Answer – Condition under which combustion can take place are as follow.
1) Air
2) Inflammable substance
3) Ignition temperature (minimum temperature at which a substance catches fire)
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 __liquefied petroleum gas (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 automobile has reduced pollution of our cities.
Answer – The use of CNG in automobile has reduced pollution in our cities because CNG does not produce any poisonous gas on burning. That is why pollution in our cities is recused.
4. Compare LPG and wood as fuels.
Answer – LPG burns easily and produces more heat in comparison to wood. Besides, it is a clean fuel, it does not produce fume and ashes as wood do. LPG can be stored and transported easily and conveniently.
5. Give reasons –
(a) Water is not used to control fires involving electrical equipment.
Answer – Water is not used to control fire produced by electrical equipment because water is conductor of electricity and may result in electrical shock.
(b) LPG is a better domestic fuel than wood.
Answer – LPG is a substance which is rapidly available. It is a cheaper and burns easily in air at moderate rate. It produce large amount of heat and does not leave behind any undersirable substance.
(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.
Answer – Paper catches fire easily, but when it is wrapped around an aluminium pipe, the ignition temperature does not meet as heat is transferred to aluminium to lower the temperature of paper.
6. Make a labelled diagram of a candle flame.
Answer –
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 as per kg (kJ/kg).
8. Explain how CO2 is able to control fires.
Answer – Carbon dioxide being heavier than oxygen covers the fire like a blanket. The added advantage of carbon dioxide is that in most cases It does not harm electrical appliance.
9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Answer – Green leaves contain lot of water. So, when we try to burn green leaves, water contained in the leaves cools the combustible materials, so that its temperature is brought below its ignition temperature. This prevents the burning of green leaves. In this case of dry leaves ,water is absent in them. So, burning process start as the temperature is raised above them ignition temperature and the leaves catch fire easily.
10. Which zone of a flame does a goldsmith use for melting gold and silver and why?
Answer – Goldsmiths use the outermost part/zone of the flame to melt gold and silver. This is because the outermost zone of the flame undergoes complete combustion and is the hottest part of the flame.
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.
A – The calorific value of fuel is the amount of heat produced by the complete combustion of 1 kg fuel.
Now,
Heat produced by 4.5 kg of fuel = 180000 kJ
Therefore heat produced by
kJ/kg
= 40,000 kJ/kg
Hence, calorific value of fuel is 40,000 kJ/kg.
12. Can the process of rusting be called combustion ? discuss
Answer –Yes, process of rusting can be called combustion. In fact, slow combustion because rusting also takes place in the air in presence of humidity in the atmosphere.
13. Abida and rakesh were doing an experiment in which water was to be heated in a breaker Abida kept the breaker 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 of ramesh beaker will get heated in a shorter time because the outermost zone of a flame is the hottest zone, while the yellow zone (in which abida had kept the beaker) is less hot.
You can check the Complete Science Solution here – NCERT Class 8th Science Solutions – Complete Solution List
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