question_answer 92)

  Explain the following (a) Reactivity of Al decreases if it is dipped in. (b) Carbon cannot reduce the oxides of Na or Mg. (c) NaCI is not a conductor of electricity in solid state whereas it does conduct electricity in aqueous solution as well as in molten state. (d) Iron articles are galvanized. (e) Metals like Na, K, Ca and Mg are never found in their free state in nature.

Answer:

                  (a)is an oxidizing agent. When aluminium is dipped in HN03, an oxide layer of aluminium is formed on the surface of the metal, which prevents it from further reaction. Thus, reactivity of Al decreases. (b) Na, Mg, etc., metals are quite reactive and present towards the top of the reactivity series. Hence, their affinity with oxygen is higher than carbon. Therefore, their oxides are stable. To reduce them with carbon, very high temperature is required and at that temperature they will form their corresponding carbides. Hence, their oxides cannot be reduced by carbon. (c) Ions ofcannot move to carry the charge in dry or solid state as they are fixed. But they are free in molten state and in aqueous solution to carry the charge and hence,conducts electricity in molten state. (d) In galvanization a thin layer of zinc is formed over the iron articles by dipping them in molten zinc, which prevents iron from corrosion as zinc is more reactive than iron. (e) These metals are quite reactive so they cannot exist in Free State and hence, they are found in nature in the form-of their compounds.