Question

In an organic compound with molar mass 108 g, c, h, and n are present in the ratio 9: 1: 3.5 by mass. Molecular formula of the compound is:

Answer 1

The ratios of the weights of the elements present in the compound are given.

Let us assume that the weight of:

C = 9x

H = 1x

N = 3.5x

therefore,

9x+1x+3.5x = 108

x = 8

Mass of C in the compound= 9x = 9*8 = 72 g

Mass of H in the compound= 1x = 8 g

Mass of N in the compound= 3.5x = 3.5*8 = 28 g

We can calculate number of moles from the mass of the element in the compound,

Number of moles of C in the compound = 72/12 = 6

no. of moles of H in the compound = 8/1= 8

no. of moles of N in the compound = 28/14 = 2

Ratios between the number of moles of each element,

Divide the number of moles by the smallest value:

Ratio of C:N = 3

Ratio of H:N = 4

Ration of N:N = 1

Therefore, Empirical formula is C3H4N1

Empirical formula mass = (12*3) + (1*4) + (14) = 54

Number of empirical formula units = 108/54 = 2

Therefore, the molecular formula can be derived by multiplying the empirical formula by 2

= C6H2N2