Question

The molecular formula mass of this compound is 120 amu . What are the subscripts in the actual molecular formula? Enter the subscripts for C, H, and O

Answer 1

The simplest formula i.e, empirical formula of the organic molecule having molar mass 120 can be assumed to be CH₂O, because if we consider the simplest formula as CHO then empirical formula mass becomes (12+1+16)=29 which can never be possible if molecular mass of the compound is 120 as molecular formula can not be fractional. If empirical formula is CH₂O, then empirical formula mass becomes (12+2+16)=30 by which 120 is divisible. So, the molecular formula is considered as- (CH₂O)ₓ, where x= positive integer.

Mass of (CH₂O)ₓ=120, which indicates (12+2+16) X x =120

So, 30x =120, x=4.Hence the molecular formula is C₄H₈O₄.

Subscript for C=4, H=8, O=4.