Give reasons for the following:
(i) Metals are regarded as electro-positive elements.
(ii) When a piece of copper metal is added to a solution of zinc sulphate, no change takes place, but the blue colour of copper sulphate fades away when a piece of zinc is placed in its solution.
(iii) Articles made of Aluminium do not corrode even though aluminium is an active metal.
Reasons:
(i) An electro-positive element is one that has tendency to lose electrons and form cation. Metals like Na, K, Ca, Fe, Zn easily lose electrons as most of them have few electron in their valence shell. Due to this, metals are considered as electro positive.
(ii) In activity series, Zinc is placed higher than copper. So, when copper is added to Zinc sulphate solution, no reaction takes place because copper being less reactive than Zinc, can’t replace Zinc from Zinc sulphate solution. On the other hand, Zinc is more reactive than copper. When zinc is added to copper sulphate solution, it replaces copper from the solution to form colourless Zinc sulphate solution.
(iii) When Aluminium is exposed to moist air, its surface is covered with thin impervious layer of aluminium oxide. This layer does not allow moist air to come in contact with the fresh metal and hence, protect the metal underneath from further damage or corrosion.