Explain the following

Question:

Explain the following

(a) Reactivity of Al decreases if it is dipped in cone. 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 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.

Solution:

(a) When Al metal is dipped in cone. HNO3 for sometime, it is oxidised initially to aluminium oxide (Al2O3). The oxide gets deposited on the surface

of the metal and forms a protective coating an the surface. The metal is said to become passive towards air, acids and alkalies. Its reactivity

therefore, decreases.

(b) Both Na and Mg are more reactive than carbon. Therefore, carbon is not in a position to reduce the oxides of these metals.

(c) NaCl is an ionic compound. Its electrical conductivity is due to the mobility of Na+ and Cl ions. These ions cannot move in the solid state.

However, they can do so either in molten state of the salt or when it forms and aqueous solution in water.

(d) Iron has a tendency to get rusted in atmosphere by reacting with oxygen and water vapours present in air. In order to check rusting, iron

articles are generally coated with zinc. This process is known as galvanization.

(e) All these metals are placed high in reactivity series of metals. They are quite reactive and do not exist in free states.

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