Chemistry: The Solid State

Q. Teacher explained the stoichiometric defects in a class room. 

 a) Explain with the help of diagrams the important differences in Schottky and Frenkel defects.

 b) What are the consequences?

Q.  a) Write an equation for the calculation of density of a crystal from its structure?

b) Calculate the density of PbS crystal (fcc)  if the edge length of its unit cell is 500pm. (NA = 6.022 x 1023, atomic mass of Pb = 207.2, S = 32) 

Q.  Defects are found even in crystals prepared very carefully.
     a) Which stoichiometric defect causes decrease in density of the solid?
     b) Frenkel defect is not found in NaCl. Why?
     c) KCl crystal is colourless.But on heating it in an atmosphere of potassium vapour, it becomes
 violet in colour.Account for this.

Q.  In magnesium crystal, the layers of atoms are being stacked in a pattern AB AB AB …… type of arrangement.
    a) Name the close packed structure.
    b) Calculate the number of tetrahedral and octahedral voids, if the Mg crystal contains ‘n’ atoms.


 Q. a) Schottky and Frenkel defects are two stoichiometric defects shown by crystals.
      i) Classify the crystals into those showing Schottky defects and Frenkel defects: NaCl, AgCl,CsCl,CdCl2
      ii) Name a crystal showing both Schottky defect and Frenkel defect.
      b) Schematic alignment of magnetic moments of ferromagnetic, antiferromagnetic and ferrimagnetic substances are given below. Identify each of them