Question

An organic compound, X, has the following composition by mass. It is 62% by mass carbon and 24.1% by mass nitrogen, with the remainder being hydrogen. (a) Determine the percentage by mass of hydrogen, and the empirical formula of X. (b) Define the term relative molecular mass. c) The M, of the compound X is 116. Determine the molecular formula of X.

Answer 1

100 g of compound will contain 62.07 g of C, 10.34 g of H, 14.0 g of N and 13.59 g of O.

The atomic masses of C, H, N and O are 12 g/mol, 1 g/mol, 14 g/mol and 16 g/mol respectively.

The number of moles of C =

12 g/mol

62.07 g

=5.17 mol.

The number of moles of H =

1 g/mol

10.34 g

=10.34 mol.

The number of moles of N =

14 g/mol

14 g

=1 mol.

The number of moles of O =

16 g/mol

13.59 g

=0.85 mol.

The mole ratio C:H:N:O=5.17:10.34:1:0.85≃5:10:1:1

Hence, the empirical formula is C

5

H

10

NO

The empirical formula mass =5(12)+10(1)+14+16=100 g/mol

The ratio of molecular formula mass to empirical formula mass =

100

144

=1.44

Hence, the molecular formula of organic compound is (C

5

H

10

NO)

1.44

.