Question

What is meant by saying that ‘the molecular mass of oxygen is $32$ ‘?

Answer 1

Hint : Oxygen is an element belonging to the sixteenth group of the modern periodic table. The atom contains a particular amount of mass in its nucleus, but here we talk about oxygen gas which is a diatomic molecule which consists of both the oxygen atoms connected to each other through a double bond.

Complete Step By Step Answer:
The atomic mass is a measure of the total matter contained in an atom. When two or more atoms combine through covalent or ionic interactions then a molecule is formed.
According to the law of definite proportions, each compound or molecule contains the exact same proportion of elements by masses. Thus, irrespective of the source from which we extract oxygen, pure oxygen gas always contains diatomic oxygen molecules as their basic unit.
The mass present in any atom is due to the presence of protons and neutrons inside the nucleus. The oxygen atom has an atomic number of eight i.e. eight protons are present in its nucleus. It also contains an equal number of neutrons. Thus, the total mass number of a single oxygen atom is $16$ .
Therefore the statement ‘the molecular mass of oxygen’ indicates that the oxygen molecule contains two identical oxygen atoms of $16amu$ resulting in a molecular mass of $16 \times 2 = 32amu$ .
The molar mass i.e. mass of one mole of oxygen gas will be numerically the same as that of molecular mass but with different units. Thus the given statement also suggests that the molar mass of oxygen gas is $16 \times 2 = 32gmo{l^{ - 1}}$ .

Note :
The number of protons and neutrons are exactly the same inside the oxygen atom but this is not a necessary condition. An atom can have an unequal number of protons or neutrons. But a neutral atom must have the same number of protons and electrons.