Solid State - Result Question 44

####44. Chromium metal crystallises with a body centred cubic lattice. The length of the unit edge is found to be 287pm. Calculate the atomic radius. What would be the density of chromium in g/cm3 ?

(1997, 3M)

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Answer:

Correct Answer: 44. (7.3g/cm3)

Solution:

  1. In bcc unit cell, 4r=3a

r(Cr)=3a4=34×287pm=124.3pm

Density of solid =NMNAa3

N= Number of atoms per unit cell, M= Molar mass

a3= Volume of cubic unit cell, NA= Avogadro’s number

=2×52g6.023×1023×(12.87×108cm)3=7.3g/cm3



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