Chemistry
Give reasons
(a) Hydrogen is collected by the downward displacement of water and not of air, even though it is lighter than air.
(b) A candle brought near the mouth of a jar containing hydrogen gas starts burning but is extinguished when pushed inside the jar.
(c) Apparatus for laboratory preparation of hydrogen should be airtight and away from a naked flame.
Hydrogen
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Answer
(a) Hydrogen is collected by the downward displacement of water as it forms an explosive mixture with air and therefore, cannot be collected by downward displacement of air even though it is lighter than air.
(b) Hydrogen is a combustible gas but it does not support the combustion process, hence, when a candle is brought near the mouth of a jar containing hydrogen gas, it starts burning but is extinguished when pushed inside the jar.
(c) Apparatus for the laboratory preparation of hydrogen should be airtight because hydrogen forms an explosive mixture with air. Hydrogen is a highly flammable gas, if a naked flame is present near the apparatus, it can lead to an ignition of the hydrogen, resulting in an explosion.
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