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  • 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

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.

Answers (1)

(a) Nitric acid (HNO3) is a strong oxidizing agent. When aluminium (Al) is dipped in HNO3, an oxide layer of aluminium (Al2O3) is formed on the surface of the metal, which prevents it from further reaction. Thus, reactivity of Al decreases.

(b) Affinity of Na, Mg with oxygen is higher than that of carbon. This is because Na, Mg metals are quite reactive and present towards the top of the reactivity series. Therefore, their oxides (Na2O, MgO) are stable. Very high temperature is required to reduce them with carbon, and at that temperature they will form their corresponding carbides. Hence, their oxides cannot be reduced by carbon

(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. Ions of NaCl are free to move in aqueous solution to carry the charge. But in dry or solid state, ions of NaCl cannot move to carry the charge in as they are fixed. Hence, NaCl conducts electricity in molten state.

(d) Galvanization is a method of protecting iron from rusting by coating it with a thin layer of zinc (Zn) metal.

A thin layer of zinc is formed over the iron articles by dipping them in molten zinc. As zinc is more reactive than iron, this prevents iron from corrosion

(e) Metals like Na, K, Ca and Mg are never found in their free state in nature because 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.

 

 

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