Solid State - Result Question 7

####7. A solid having density of 9×103kgm3 forms face centred cubic crystals of edge length 2002pm. What is the molar mass of the solid?

[Avogadro constant =6×1023mol1,π=3]

(2019 Main, 11 Jan I)

(a) 0.03050kgmol1

(b) 0.4320kgmol1

(c) 0.0432kgmol1

(d) 0.0216kgmol1

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Answer:

Correct Answer: 7. (a)

Solution:

  1. Density of a crystal

d=M×ZNA×a3M=d×NA×a3Z

Given, d=9×103kgm3

M= Molar mass of the solid  Z=4( for fcc crystal ) NA= Avogadro’s constant =6×1023mol1 a= Edge length of the unit cell  =2002pm=2002×1012m

On substituting all the given values, we get

=(9×103)kgm3×(6×1023)mol1×(2002×1012)3m34 =0.0305kgmol1



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