The Law of Definite Proportions

Learning Objectives:

Students confirm The Law of Definite Proportions: different samples of a pure compound always contain the same elements in the same proportions by mass.


Students thermally decompose a sample of potassium chlorate, releasing oxygen molecules. They determine the decrease in mass due to lost oxygen and calculate the mass percent of oxygen in potassium chlorate. They can use this knowledge of proportions to make other calculations.