Q5 / 164 · NTA Abhyas (NEET) 2020 · Chemistry · Solid State

A compound AB has a rock type structure with A : B = 1 : 1. The formula weight of AB is 6.023 y amu and the closest A – B distance is y1/3 nm. The density of lattice is?

  • A
    1.5 kgm-3
  • B
    2.5 kgm-3
  • Correct answer
    C
    5.0 kgm-3
  • D
    7.5 kgm-3

Solution

AB has rock-salt (A : B :: 1 : 1) structure, i.e., fcc structure (n = 4) and formula weight of AB is 6.023 y g having closest distance A – B y1/3 nm. Therefore, edge length of unit cell
(a)=2(A++B-)=2×y1/3×10-9m
So density of AB =n×mol.wt.Av.no.×V=n×mol.wt.6.023×1023×a3
=4×6.023×y×10-36.023×1023×(2y1/3×10-9)3 (mol. wt. in kg)
=5.0 kgm-3

Hence, the correct answer is option: 'C'.

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