Q19 of 68 Page 29

What type of defect can arise when a solid is heated? Which physical property is affected by it and in what way?

When a solid is heated, vacancy defect is produced in the crystal. On heating, some ions or atoms leave the lattice site completely, which means the lattice site becomes empty or vacant. As a result of this defect, density of the substance decreases. Thus density is the physical property that is effected by the vacancy defect.


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17

Which of the following lattices has the highest packing efficiency

(i) simple cubic


(ii) body-centred cubic and


(iii) Hexagonal close-packed lattice?

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An element with molar mass 2.7×10-2 kg mol-1 forms a cubic unit cell with edge length 405 pm. If its density is 2.7×103 kg m-3, what is the nature of the cubic unit cell?

 20

What type of stoichiometric defect is shown by?

(i) ZnS (ii) AgBr

 21

Explain how vacancies are introduced in an ionic solid when a cation of higher valence is added as an impurity in it.