10th Class Science Metals and Non-metals Question Bank 10th CBSE Science Metals and Non-metals

  • question_answer   Give reasons: (a) Platinum, gold and silver are used to make jewellery. (b) Sodium, potassium and lithium are stored under oil. (c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking. (d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction. (e) Lemon or tamarind juice are effective in cleaning tarnished copper vessels. [CBSE Delhi 2008C]

    Answer:

                      (a) Platinum, gold and silver are used to make jewellery because of their bright shiny surface and high resistance to corrosion. Also they have high malleability and ductility. (b) Sodium, potassium and lithium are stored under oil to prevent their reaction with oxygen, moisture and carbon dioxide of air so as to protect them. (c) Aluminium metal forms a thin layer of aluminium oxide all over its surface under the action of moist air. This layer prevents the metal underneath from further corrosion. It is cheap, easily available, malleable and ductile. Therefore, it is used to make utensils for cooking. (d) It is easier to obtain a metal from its oxides as compared to its sulphides and carbonates. So, prior to reduction, metal carbonate and sulphides must be converted into metal oxides. A carbonate ore is converted into oxide by calcination whereas a sulphide ore is converted into oxide by roasting. (e) When copper vessels are exposed to moist air, they form a green coating of basic copper carbonate [CuCO3. Cu(OH)2]. The sour substances such as lemon or tamarind juice contain acids. Lemon juice contains citric acid and tamarind contains tartaric acid. These acids dissolve the coating of copper oxide or basic copper carbonate present on the surface of tarnished copper vessels and make them shining red-brown again.


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