The Solid State — Chemistry STD 12 Science — Question
Gujarat BoardEnglish MediumSTD 12 ScienceChemistryThe Solid State2 Marks
Question
Explain how vacancies are introduced in an ionic solid when a cation of higher valence is added as an impurity in it.
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Answer
If we mix a small amount of molten strontium chloride $\left(\mathrm{SrCl}_2\right)$ with molten sodium chloride $(\mathrm{NaCl})$ and the resulting solution is cooled, in the crystals of NaCl some $\mathrm{Na}^{+}$ions will get replaced by $\mathrm{Sr}^{2+}$ ions. In order to maintain electron neutrality too $\mathrm{Na}^{+}$ions are to leave their respective lattice sites. However, one out of them will be occupied by the $\mathrm{Sr}^{2+}$ ion while the other will remain unoccupied or it will be vacant. Thus vacancies are introduced in an ionic solid.
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