Question

A compound of molar mass 161 g/mol contains only carbon, hydrogen, bromine, and oxygen. Analysis reveals that the compound contains 12 times as much carbon as hydrogen by mass. Find the molecular formula.

Answer 1

The molecular formula is C₅H₅OBr

Solution and explanation:

The molar mass of the compound is 161 g/mol

Elements contained in the compound are carbon, hydrogen, bromine, and oxygen.

Atomic masses are;

Oxygen - 16.0 g/mol

Bromine - 79.90 g/mol

Carbon - 12.01 g/mol

Hydrogen - 1.008 g/mol

Assuming the compound contains 1 mole of Bromine and Oxygen

Therefore;

Total mass of bromine and oxygen in the compound= 16.0 g/mol + 79.90 g/mol

If there are x atoms of hydrogen in the compound, then;

Mass of Hydrogen = 1.008 x

Carbon is 12 times the mass of hydrogen, thus

`Mass of Carbon = 12(1.008x)\\= 12.096x`

Hence;

`161 g/mol = 12.096x + 1.008 x + 16.0 g/mol + 79.90g/mol\\65.1 g/mol  = 13.104x\\x = 4.9679\\= 5`

Therefore;

Hydrogen atoms = 5

Carbon atoms= 5(12.096)/12.01

= 5

Bromine atoms = 1

Oxygen atom = 1

Therefore;

The molecular formula is C₅H₅OBr