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A. Answer the following questions.1.What happens when-a. Hydrogen is passed over red hot copper oxide.b. Hydrogen reacts with molten sulphur.c. Zinc reacts with dilute hydrochloric acid.d. Calcium reacts with cold water

Answer»

a) Metallic copper and water vapour will be formed when hydrogen is passed over heated copper(II) oxide.

CuO + H2 = Cu + H2O

Hydrogen reduces cupric oxide to free metal in this reaction.

b) Hydrogen gas will react with molten sulfur (around 450*C) to form gaseous hydrogen sulfide, H2S. It has a characteristic smell of rotten eggs, is poisonous, flammable and corrosive. Some bacteria in our gut will produce H2S under certain circumstances.

c)Thereactionbetweenzincandhydrochloric acidisZn+HCl= H2 + ZnCl2. It is a single replacementreactionwherezincmetal displaces the hydrogen to form hydrogen gas andzincchloride, a salt.Zinc reactsquickly with the acid to form bubbles of hydrogen.

d) In the following demonstration, a chunk ofcalciummetal is dropped into a beaker of distilledwater. After a second or so, thecalciummetal begins to bubble vigorously as itreactswith thewater, producing hydrogen gas, and a cloudy white precipitate of calciumhydroxide.

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