Question

Lithium borohydride crystallizes in an orthorhombic system with 4 molecules per unit cell. The unit cell dimensions are a = 6.8 Angstrom , b = 4.4 A and c = 7.2 angstrom . If the molar mass is 21. 76g , calculate density of Crystal

Answer 1

volume of the unit cell = abc =6.8*4.4*7.2

=215.424 A³ = 2.154 *10^-22 cc

each unit cell has 4 molecules so mass of each unit cee = 4*21.76/(6.023 *10²³) =1.445 * 10^-22 gm

so
density = mass/volume
=1.445 * 10^-22 gm/2.154 *10^-22cc

=.671 gm/cc