(a) Determine the type of cubic lattice to which a given crystal belongs if it has edge length of 290 pm and density is 7.80 g cm–3. (Molecular mass.= 56 g mol–1)
(b) Why does zinc oxide exhibit enhanced electrical conductivity on heating?
we know that
as we have given
d= 7.80 g cm–3.
M=56 g mol–1
a= 290 pm or a3 =2.43 x10-23
putting all value in above equation we get,
hence it belong to bcc crystal lattice.
b) Zinc oxide is white in colour at room temperature. On heating it loses electron and turns yellow in colour.
The electron liberate after heating, can act as charge carrier and thus on heating zinc oxide it exhibit electrical conductivity.
Formula mass of CuCl =63.5 +35.5
= 99.0
The number of formula units per cell of ZnS is 4. It has face centred cubic structure.
we have
edge length =200Pm
volume of the unit = ( 200 x10-10 cm)3
= 8 x10-24 cm-3
density = 41.6 g cm-3.
we have given,
Mass= 209 g
Number of atom per unit cell =1 (Simple cubic)
density =91.5 g m-3
NA =6.023 x1023
edge length of unit cell =?
By applying formula
a= 15.59 x10-8 cm
Let ‘a’ be the edge length of the unit cell and r be the radius of sphere.
As sphere are touching each other
Therefore a = 2r
No. of spheres per unit cell = 1/8 × 8 = 1
Volume of the sphere = 4/3 πr3
Volume of the cube = a3= (2r)3 = 8r3
∴ Fraction of the space occupied = 1/3πr3 / 8r3 = 0.524
∴ % occupied = 52.4 %