When a lot of dry powder of a substance X is released over a fire, the fire gets extinguished.
(a) Name the substance X.
(b) How does the substance extinguish the fire ?
(c) Name another substance which behaves like X.
(a) Sodium hydrogen carbonate.
(b) The heat of fire decomposes sodium bicarbonate to produce carbon dioxide gas. This carbon dioxide covers the fire like a blanket and cuts off supply of air to the burning substance. Due to this the fire gets extinguished.
(c) Potassium hydrogen carbonate.
How does carbon dioxide help in putting off fire ?
Carbon dioxide covers the surface of the burning substance and act as blanket and hence does not allow the oxygen to reach the substance. In absence of oxygen the fire gets put off.
An electric spark is struck between two electrodes placed near each other in a closed tank full of petrol. Will the petrol catch fire ? Explain your answer.
No, the petrol will not catch fire. This is because in a closed tank full of petrol, there is no air to support the combustion of petrol. In the absence of supporter of combustion, petrol cannot burn or catch fire.
Give reason for the following :
Paper by itself catches fire easily where as a piece of paper wrapped around an aluminium pipe does not.
When paper is heated alone, its ignition temperature is reached quickly due to which it catches fire easily. When the paper wrapped around an aluminium pipe is heated, then the heat supplied to paper is transferred to aluminium pipe by conduction. Due to the continuous transfer of heat from paper to aluminium pipe, the paper does not got heated to its ignition temperature quickly and hence does not catch fire easily.
What type of combustion is represented by :
(a) burning of white phosphorus in air at room temperature ?
(b) burning of LPG in a gas stove ?
(c) ignition of a cracker ?
(d) burning of coal dust in a coal mine ?
(a) Spontaneous combustion.
(c) Rapid combustion.
(c) Explosive combustion (or Explosion).
(d) Spontaneous combustion.
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