Chemistry
(a) Name the chemicals required to prepare hydrogen gas in the laboratory.
(b) Give a balanced chemical equation for the reaction.
(c) Draw a neat and well-labelled diagram for the laboratory preparation of hydrogen.
(d) How is hydrogen gas collected? Why?
(e) Give one chemical test for hydrogen. Why?
Hydrogen
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Answer
(a) Granulated zinc and dilute hydrochloric acid are the chemicals required to prepare hydrogen gas in the laboratory.
(b) Zn + 2HCl ⟶ ZnCl2 + H2 (g)
(c) Below diagram shows the laboratory preparation of Hydrogen gas:
(d) Hydrogen gas is collected by downward displacement of water as it is sparingly soluble in water. Though hydrogen gas is lighter than air, it is not collected by downward displacement of air as a mixture of hydrogen and air can lead to an explosion.
(e) Hydrogen gas burns in air with a pop sound. This is because of the presence of impurities in it. This method is widely used as a test to identify hydrogen.
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Hydrogen is the most abundant element in the universe. On earth, however, it is rarely found in the free state because of its high reactivity, and usually occurs in combined forms such as water and hydrocarbons. Owing to its unique properties, hydrogen has a wide range of applications. It is used in cutting and welding metals, as a reducing agent for extracting metals from their oxides, in the preparation of vanaspati ghee from vegetable oils and in the manufacture of many important chemicals. Today, hydrogen is widely regarded as a potential clean fuel of the future.
(a) Why is hydrogen known as a clean fuel ?
(b) Define the process used to prepare vanaspati ghee from vegetable oils. Name a catalyst used in this process.
(c) Why is hydrogen used for cutting and welding metals ?
(d) Why is hydrogen not used in weather forecasting balloons anymore ?
(e) Name the gas which has replaced hydrogen in these balloons. Why ?