A crystalline solid of a pure substance has a face-centred cubic structure with a cell edge of 400 pm. If the density of the substance in the crystal is 8 g c m - 3 , then the number of atoms present in 256 g of the crystal is N × 1 0 24 . The value of N is

Question

A crystalline solid of a pure substance has a face-centred cubic structure with a cell edge of 400 pm. If the density of the substance in the crystal is 8 g c m - 3 , then the number of atoms present in 256 g of the crystal is N × 1 0 24 . The value of N is,

MARKS App · Accepted Answer

d = Z × M 0 N A a 3 (d = density) 8 = 4 × M 0 6 × 1 0 23 ( 4 × 1 0 - 10 ) 3 M 0 = 1 8 × 6 × 1.6 Number of moles in 256 g = 256 8 × 6 × 1.6 = 10 3 Number of atoms = 10 3 × 6 × 1 0 23 = 2 × 1 0 24

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