Ncert Exercises & Solutions

Which of the following statement indicates that the law of multiple proportions is being followed?

1.	A sample of carbon dioxide taken from any source will always have carbon and oxygen in the ratio of 1:2.
2.	Carbon forms two oxides namely, CO₂ and CO, where masses of oxygen that combine with a fixed mass of carbon are in the simple ratio of 2:1.
3.	When magnesium burns in oxygen, the amount of magnesium used for the reaction is equal to the amount of magnesium formed in magnesium oxide.
4.	At constant temperature and pressure, 200 mL of hydrogen will combine with 100 mL of oxygen to produce 200 mL of water vapour.

Hint: Law of multiple proportion.

Explanation:

The element, carbon, combines with oxygen to form two compounds, namely, carbon dioxide and carbon monoxide. In CO₂,

12 parts by mass of carbon combine with 32 parts by mass of oxygen while in CO, 12 parts by mass of carbon combine with

16 parts by mass of oxygen.

Therefore, the masses of oxygen combine with a fixed mass of carbon (12 parts) in CO₂ and CO are 32 and 16 respectively.

These masses of oxygen bear a simple ratio of 32 : 16 or 2 : 1 to each other.

This is an example of law of multiple proportion.