Question

Explain solid solutions of metals and vacancy through aliovalent cations.

Answer 1

1. Solid solutions of metals (alloys):
   
   Brass
   Brass is an alloy of Cu and Zn. In brass, host Cu atoms are replaced by impurity of Zn atoms. The Zn atoms occupy regular sites of Cu atoms as shown in the figure.
2. Formation of vacancy through aliovalent impurity:
   Vacancies are created by the addition of impurities of aliovalent ions (that is, ions with oxidation state different from that of host ions) to an ionic solid.
   e.g. Consider a small amount of SrCl₂ impurity added to NaCl during its crystallization. The added Sr²⁺ ions (O.S. = +2) occupy some of the regular sites of Na+ host ions (O.S. = +1). In order to maintain electrical neutrality, every Sr²⁺ ion removes two Na⁺ ions. One of the vacant lattice sites created by removal of two Na⁺ ions is occupied by one Sr²⁺ ion. The other site of Na⁺ ion remains vacant as shown in the figure.
   
   Vacancy through aliovalent ion