Law of multiple proportions

John Dalton (1803) stated this law as 'when two elements combine with each other to form two or more than two compounds, the mass of the element which combine with the fixed mass of the other bears a simple whole number ratio'.

Examples 3:

Carbon monoxide (CO): 12 parts by mass of carbon combines with 16 parts by mass of oxygen.

Carbon dioxide (CO2): 12 parts by mass of carbon combines with 32 parts by mass of oxygen.

Ratio of the masses of oxygen that combines with a fixed mass of carbon (12 parts) 16: 32 or 1: 2

For example, hydrogen and oxygen are known to form 2 compounds. The hydrogen content in one is 5.93% while in the other it is 11.2%. Show that this data illustrates the law of multiple proportions.

Solution:

In the first compound hydrogen = 5.93%

Oxygen = (100 -5.93) = 94.07%

In the second compound hydrogen = 11.2%

Oxygen = (100 -11.2) = 88.88%

Ratio of the masses of oxygen that combine with fixed mass of hydrogen 15.86: 7.9 or 2:1

The ratio illustrates the law of multiple proportions.