Explain the following.
(a) Reactivity of Al decreases if it is dipped in HNO3
(b) Carbon cannot reduce the oxides of Na or Mg.
(c) NaCl 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 galvanised.
(e) Metals like Na, K, Ca and Mg are never found in their free state in nature.
(a) When aluminium (Al) is dipped in nitric acid (HNO3), a layer of aluminium oxide is formed on the metal. This happens because nitric acid is a strong oxidizing agent. The layer of aluminium oxide prevents further reaction of aluminium. This is the reason why the reactivity of aluminium decreases.
(b) Sodium and magnesium have tendency to react with oxygen rather than carbon because these are highly reactive metals. Hence, carbon cannot reduce the oxides of Na or Mg.
(c) Ionic compounds do not conduct electricity in solid state but they conduct electricity in aqueous solution and in molten state due to high concentration of free electrons. This property is shown by sodium chloride as it is an ionic compound.
(d) Iron articles are galvanized to prevent them from rusting. After galvanization, the layer of zinc works as protective layer. The most common type is hot-dip galvanizing. In this process, iron parts are submerged in a bath of molten zinc.
(e) Metals such as Na, K, Ca and Mg are highly reactive metals and hence they are not found in their free state in nature.