. In an organic compound of molar mass greater
than 100 containing only C, H and N , the percentage of C is 6 times the percentage of
H while the sum of the percentages of C and H is 1.5 times the percentage of N . What is the least molar mass?
Let the compound be CxHyNz.
Mass of C=12x
Mass of H=y
Mass of N=14z
Total Mass =12x+y+14z
Mass % of C= 13x /(12x+y+14z) ×100
(I) Mass % of C=6× mass % of H
(II) Mass % of C + Mass % of H =1.5 (mass % of N)
So, the compound can be expressed as or C1.5zH3zNz or C3zH6zN2z.
Now choosing,z=1 , we have C3H6N2.
Molecular weight =3×12+6×1+2×14=70 g/mol
Given molecular weight >100.
So, when we choose z=2, we have C6H12N4.
Molecular weight which is greater than =6×12+12×1+4×14=140 g/mol which is greater then 100.
The correct option is B: 140