Explain the following
(a) The reactivity of a piece of aluminium metal decreases if it is dipped in HNO3
(b) Carbon cannot reduce the oxides of Na or Mg
(c) NaCl does not conduct electricity in solid state whereas it does conduct electricity in aqueous solution as well as in molten state
(d) Necessity of galvanisation of iron articles
(e) Metals like Na, K, Ca and Mg are never found in their free state in nature.
OR
Given below are the steps for extraction of copper from its ore.
(a) Write the equations of the reactions involved in roasting of copper (I) sulphide followed by its reduction.
(b) Draw a neat labelled diagram for electrolytic refining
(a) As HNO3 is an oxidising agent. So, when aluminium is dipped in HNO3 a layer of aluminium oxide is formed on the surface of the metal, which prevents it from further reactions with other compounds.
(b) Na, Mg metals are quite reactive and are present at the top of the reactivity series. Hence, their affinity towards oxygen is quite high and their oxides cannot be reduced by carbon.
(c) Ions of NaCl cannot move to carry/transport the charges in dry state due to electrostatic forces of attraction by neighboring atoms, But, they are free to move in molten state and in aqueous solution to carry the charge. So, NaCl conducts electricity in molten state as well as in aqueous solution but not in dry state.
(d) Galvanisation is required as it prevents iron articles from corrosion in galavanistion a thin layer of zinc is formed over the iron articles by dipping them in molten zinc, which prevents iron from corrosion.
(e) Metals like Na,K,Ca and Mg are quite reactive so, they cannot exist in free state and hence they are found in nature in form of their compounds
Example: NaCl, KCl , CaCO3 ,MgO etc.
OR
(a) The equations involved are written as:
2Cu2S (s) + 3O2 (g)→ 2Cu2O (s) + 2SO2 (g) [Oxidation]
2Cu2O (s) +Cu2S(s) → 6Cu (s) + SO2 (g) [Reduction]
(b) The process of electrolytic refining is explained as:
