Chemistry
Give the reason for the following
(a) Zinc granules are used in the lab preparation of hydrogen.
(b) Purified and dried hydrogen is collected over mercury.
(c) The end of the thistle funnel should be dipped under acid.
(d) Dilute sulphuric acid cannot be replaced by concentrated acid in the preparation of hydrogen.
Answer
(a) Granulated zinc contains traces of impurities like copper, which has a slight catalyzing effect on the reaction and speeds it up. Hence, granulated zinc is preferred in the lab preparation of hydrogen over pure zinc.
(b) Hydrogen gas is purified and dried and then collected over mercury because mercury has no reaction with it.
(c) The end of the thistle funnel should be dipped under acid so as to prevent gas from escaping the thistle funnel.
(d) Dilute Sulphuric acid cannot be replaced by concentrated acid in the preparation of hydrogen as it is a strong oxidiser and it will produce sulphur dioxide.
Zn + 2H2SO4 ⟶ ZnSO4 + SO2 + 2H2O
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