Class 12

Chemistry

Gases & Solutions

States of Matter

$CsBr$ crystallises in a body$−$ centred cubic lattice. The unit cell length is $436.6pm$. Given that $:$ the atomic mass of $Cs=133$ and that of $Br=80amu$ and Avogadro's number being $6.02×10_{23}mol_{−1}$, the density of $CsBr$ is $:$

- $42.5g/cm_{3}$
- $0.425g/cm_{3}$
- $8.25g/cm_{3}$
- $4.25g/cm_{3}$

$Z→number of atoms in the bcc unit cell=2$

$M→molar mass of CsBr=133+80=213$

$a→edge length of unit cell=436.6pm$

$=436.6×10_{−10}cm$

$∴Density=(436.6×10_{−10})_{3}×6.023×10_{23}2×213 $

$=8.49×10_{−7}×10_{7}g/cm_{3}$

$=8.50g/cm_{3}$

For a unit cell $=28.50 =4.25g/cm_{3}$