The Solid State

Question 97
CBSEENCH12005445

What is possible formula of a compound which is made of two elements P and Q and forms fcc structure. Atoms P occupy corner positions and Q occupy face positions of cube?

Solution
In a fcc unit cell, there are 8 corners and 6 faces. Eight corners contribute 8 x 1/8 = 1 atom
six faces contribute 6 x 1/2 = 3 atoms.
So the formula of the compound is PQ
3.
Question 98
CBSEENCH12005446

What is the general structure of ionic solids?

Solution
In ionic solids, generally anions form close-packed structure and cations occupy interstitial sites. example NaCl, KCl. These are ionic solids
Question 99
CBSEENCH12005447

How many octahedral voids are there in 1 mole of a compound having cubic closed packed structure? 

Solution
There are 1 mole of octhahedral voids in every one mole ofthe compound cotaining ccp structure.
since number of particles present in 1 mole compound =6.022 x 1023 
we know that number of octahedral voids=number of atoms in structure.
Question 100
CBSEENCH12005448

What is the two-dimentional coordination number of a molecule in square closed packed layer ?

Solution
The coordination number is 4.

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