Question

An organic compound crystallises in an orthorhombic
cell in the ratio of 2:1. The dimensions of cell are
12.05, 15.05 and 2.69 Å and density is 1.419 g/cm3.
Molar mass of the compound is-
@ 207g.mol-1
© 308g.mol-1
6 209g.mol-1
0 317g.mol-1
01:00
The
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Answer 1

Answer:

Density, ρ=a3×NAZ×M

Given,

Orthorhombic system has different edge length, width and height

∴a=12.05Ao=12.05×10−8 cm

b=15.05Ao=15.05×10−8 cm

c=2.69Ao=2.69×10−8 cm

∵ System has 2 molecules per unit cell,

∴Z=2

and NA=6.023×1023

Now, molecular mass will be

 

M=Zρ×a×b×c×NA

M=21.419×12.05×10−8×15.05×10−8×2.69×10−8×6.023×1023

M=2084.6×10−1=209 gmol−1.