Question: 37 - Iqbal treated a lustrous, divalent element M with sodium hydroxide. He observed the formation of bubbles in reaction mixture. He made the same observations when this element was treated with hydrochloric acid. Suggest how can he identify the produced gas. Write chemical equations for both the reactions.
Answer: In the first case; a base reacts with a metal, and in the second case; an acid reacts with a metal. Hence, hydrogen gas is most likely to be produced during these reactions.The evolution of hydrogen gas can be checked by bringing a burning matchstick or splinter near the evolved gas. The fact that the matchstick burns with a pop sound, shows that hydrogen gas is evolved.
The reactions can be shown by following equations:
2NaOH + Zn → Na2ZnO2 + H2
2HCl + Zn → ZNCl2 + H2
Question: 38 - During extraction of metals, electolytic refining is used to obtain pure metals.
(a) Which material will be used as anode and cathode for refining of silver metal by this process?
Answer: In electrolytic refining, impure metal is always used as anode and pure metal is used as cathode. Metals are electropositive in nature and hence they are released from anode and get deposited on cathode. Hence, impure silver will be used as anode and pure silver will be used as cathode
(b) Suggest a suitable electrolyte also.
Answer: Silver chloride
(c) In this electrolytic cell, where do we get pure silver after passing electric current?
Answer: At cathode
Question: 39 - Why should the metal sulphides and carbonates be converted to metal oxides in the process of extraction of metal from them?
Answer: Obtaining a metal from its oxide is much easier than doing that from a metal sulphide or carbonate. Due to this; metal sulphides and carbonates are first converted to metal oxides during metallurgy.
Question: 40 - Generally, when metals are treated with mineral acids, hydrogen gas is liberated but when metals (except Mn and Mg), treated with HNO3, hydrogen is not liberated, why?
Answer: Most of the metals do not react with HNO3 because nitric acid is a strong oxidizing agent. Hence, when metals (except Mn and Mg) are treated with nitric acid; hydrogen gas is not liberated.
Question: 41 - Compound X and aluminium are used to join railway tracks.
(a) Identify the compound XAnswer: Iron oxide (Fe2O3)
(b) Name the reaction
Answer: Thermit reaction
(c) Write down its reaction.
Answer: Fe2O3 + 2Al → 2Fe + Al2O3 + heat
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