Question

An alkane has C/H ratio(by mass) of 5.1428. its molecular formula is

Answer 1

the general formula of alkane is CnH(2n+2)
ratio by mass of (C/H) = 5.1428

mass of (C/H) = mass of n atom of C / mass of 2n+2 atom of H
                       = (mass of 1 C atom x n) / ( mass of 1 H atom x 2n+2 )
(12 x n) / [1 x (2n+2) ]= 5.1428 

12n / (2n+2) = 5.1428
12n = 5.1428 (2n+2)
6n = 5.1428n + 5.1428
n = 5.999 ≈ 6

so structural formula is C6H14 

i hope it will help you 
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