NEET Chemistry The Solid State Questions Solved


How many unit cells are present in a cube shaped ideal crystal of NaCl of mass 1.00g?

[ Atomic masses Na=23, Cl = 35.5]

(a) 2.57 x 1021

(b) 5.14 x 1021

(c) 1.28 x 1021

(d) 1.71 x 1021

(a) Mass of one unit cell = V x d (V is volume, d is density) 

= a3 x d

Also, density = (n x at. mass) /(a3 x av.no.)

Mass of one unit cell = (a3 x n x at.mass) / (a3 x av.no.) = (n x at. mass )/(av.no.)

= 4x58.5 / 6.02 x 1023 (n=4 for cubic shape)

=38.87 x 10-23g

No. of unit cell in 1g = 1/38.87x10-23 = 2.57 x 1021

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