The Solid State - Result Question 15

####15. A metal has an fcc lattice. The edge length of the unit cell is 404pm. The density of the metal is 2.72gcm3. The molar mass of the metal is : (NA., Avogadro’s constant .=6.02×1023mol1)

(a) 30gmol1

(b) 27gmol1

(c) 20gmol1

(d) 40gmol1

[NEET 2013]

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Solution:

  1. (b) Density is given by

d=Z×MNAa3; where Z= number of formula units present in unit cell, which is 4 for fcc

a= edge length of unit cell. M= Molecular mass

2.72=4×M6.02×1023×(404×1010)3

(1pm=1010cm)

M=2.72×6.02×(404)34×107=26.99=27gmol1



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