 # Solid State Important Questions

Given below are the Solid State Class 12 Important Questions
a. Concepts questions
b. Calculation problems
d. Cubic cell problems

Question 1
A compound is formed by 2 elements M & N. N forms ccp and atoms of M occupy 1/3rd of tetrahedral voids. What is the formula of the compound?

Question 2
An element with molar mass $2.7 \times 10^{-2}$ Kg/mol. forms a cubic units cell with edge length of 405 p. m. If the density is $2.7 \times 10^3 \ Kg/m^3$. Find the nature of a cubic unit cell.

$d = \frac {(Z \times M)}{(N_A \times a^3 )}$ -(1)
Now $d = 2.7 \times 10^3 \ Kg/m^3 = = 2.7 g/cm^3$.
$M = 2.7 \times 10^{-2} \ Kg/mol =27 \ g/mol$
Volume=$a^3 = (405 \ pm)^3 = (405 \times 10^{-10} \ cm)^3$
$N_A=6.02 \times 10^{23}$
Z=?
Substituting these values in (1)
$2.7 \times 10^3=\frac { Z \times 27}{6.02 \times 10^{23} \times (405 \times 10^{-10} \ cm)^3}$
Z= 3.99 = 4.
Hence the Nature of the Cubic cell is CCP

Question 3
Gold (Atomic Radius = 0.144 nm) crystallizes in FCC. Find the length of the side of the cell.

In F. C. C.
$r = \frac {a}{2 \sqrt 2}$
Therefore
$a= r \times 2 \sqrt 2 = .144 \times 2 \times 1.414=.407 \ nm$

Question 4
Alluminium crystallizes in cubic close-packed structure. it's metallic radius is 125 pico meter.
(i) Find the length of the side of the unit cell.
(ii) How many unit cells are present in 1 cm3 of element.

(i) a = ?
for C. C. P. (F. C. C.)
$r = \frac {a}{2 \sqrt 2}$
Therefore
$a= r \times 2 \sqrt 2 = 125 \times 2 \times 1.414=354 \ pm$
(ii)
1 unit cell = $a^3 = (354 \ pm)^3 = 4.4 \times 10^{-23} \ cm^3$
Number of Unit cells= $\frac {1}{4.4 \times 10^{-23}} = 2.27 \times 10^{22}$

Question 5
Non-stoichiometric cuprous oxide,(\$Cu_2O%) can be prepared in laboratory. In this oxide Cu to O ratio is slightly less than 2 : 1. Can you account for the fact that this substance is a P – type semi – conductor?

The crystal is having cation vacancy defect, having holes in the sample. Thus it’s a P – type semi conductor because the electricity conduction is due to holes.

Question 6
What type of stoichimetric defect is shown by
(i) ZnS
(ii) AgBr

(i) ZnS - Frankel defect
(ii) Ag Br -Short key Frankel defect

Question 7
Ionic solids are hard and brittle. Why?