NCERT Solutions for Class 8th Science
Chapter 6 – COMBUSTION AND FLAME
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
Q.1 List conditions under which combustion can take place.
Ans Conditions under which combustion can take place:
1) Presence of air (oxygen)
2) Combustible substance
3) Ignition temperature
Q.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 _________.
Ans (a) Burning of wood and coal causes _pollution_ of air.
(b) A liquid fuel, used in homes is _kerosene_.
(c) Fuel must be heated to its _ignition temperature_ before it starts burning.
(d) Fire produced by oil cannot be controlled by _water_.
Q.3 Explain how the use of CNG in automobiles has reduced pollution in our cities.
Q.4 Compare LPG and wood as fuels.
Q.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.
Ans (a) Water is not used to control fires involving electrical equipment because water is a good conductor of electricity and may harm those trying to douse the fire.
Q.6 Make a labelled diagram of a candle flame.
Q.7 Name the unit in which the calorific value of a fuel is expressed.
Q.8 Explain how CO2 is able to control fires.
Q.9 It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Q.10 Which zone of a flame does a goldsmith use for melting gold and silver and why?
Q.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.
Q.12 Can the process of rusting be called combustion? Discuss.
Ans Yes. This is because both the processes involve oxidation and liberation of heat. Rusting is an exothermic reaction which involves slow decay of iron and hence can be called slow combustion.
Q.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?