CBSE Class 12th Chemistry Chapter1 The Solid State -Part6

Class XII Chemistry Chapter 1 The Solid State NCERT Solution is given below.

Question 1.10:
Calculate the efficiency of packing in case of a metal crystal for
(i) simple cubic
(ii) body-centred cubic
(iii) face-centred cubic (with the assumptions that atoms are touching each other).
Answer
(i) Simple cubic
In a simple cubic lattice, the particles are located only at the corners of the cube and touch each other along the edge.

Question 1.11:
Silver crystallises in fcc lattice. If edge length of the cell is 4.07 × 10−8 cm and density is 10.5 g cm−3, calculate the atomic mass of silver.
Answer
It is given that the edge length, a = 4.077 × 10−8 cm
Density, d = 10.5 g cm−3
As the lattice is fcc type, the number of atoms per unit cell, z = 4
We also know that, NA = 6.022 × 1023 mol−1
Using the relation:

= 107.13 gmol−1
Therefore, atomic mass of silver = 107.13 u