Question

Is oxygen lighter than carbon dioxide?

Answer 1

Hint: The factor which is used to tell us something lighter or heavier is its weight. For the molecules this weight is the molecular mass. Therefore we have to compare the molecular weight of both the gases and thus we can judge which gas is heavier and which one is lighter.

Complete answer:
Oxygen is a diatomic molecule present in our surroundings. Its molecular formula is $ {O_2} $ . This shows us the two atoms of oxygen combine and make the molecule of oxygen. This is also called molecular oxygen. Now we have to find out the molecular weight of oxygen molecules.
Therefore,
Atomic weight of a oxygen atom $ = {\text{ 16 g}} $
Number of oxygen atoms in molecule $ = {\text{ 2}} $
Molecular weight of oxygen molecule $ = {\text{ 32 g}} $
Similarly carbon dioxide is a triatomic molecule. Its molecular formula is $ C{O_2} $ . It contains one carbon atom and two oxygen atoms. Therefore it contains three total atoms which is called a triatomic molecule. Now we will find out the molecular weight of the carbon dioxide a:
Atomic weight of carbon atom $ = {\text{ 12 g}} $
Atomic weight of oxygen atom $ = {\text{ 16 g}} $
Number of oxygen atoms $ = {\text{ 2}} $
Molecular weight of oxygen molecule $ = {\text{ 32 g}} $
Molecular weight of carbon dioxide molecule $ = {\text{ 1 }} \times {\text{ 2 + 32 g}} $
 $ = {\text{ 44 g}} $
Therefore it can be seen that the molecular weight of the carbon dioxide is greater than that of the oxygen molecule. Therefore we can say that oxygen molecules are lighter than carbon dioxide.

Note:
 The molecular weight refers to the weight of the whole molecule present in the environment. The molecular weight is sometimes called the molecular mass of the compound. The gas which has more weight will have more gravitational attraction also.