Question

What is the molecular weight of ${H_2}O$?

Answer 1

The molecular weight of any chemical compound refers to the ratio of mass of a sample of that particular compound and the amount of substance in that particular sample (in moles). The molar mass is actually a bulk characteristic of a substance rather than molecular. The molar mass is generally represented as $gmo{l^{ - 1}}$.

Complete step by step answer:
The molecular weight of any compound can be found out by adding the relative atomic masses of each element present in that particular compound. The number of atoms in a compound can be determined from their chemical formula.
Now, let us calculate the molecular weight of the given compound i.e. water. The chemical formula of water is given i.e. ${H_2}O$. We already know the atomic mass of hydrogen and oxygen which is mentioned below:
$H = 1.00794u \\\ O = 15.9994u \\\$
From the chemical formula, it is clear that water comprises of two atoms of hydrogen and one atom of oxygen and thus molecular weight of this compound can be easily calculated by adding the mass of two hydrogen atoms and one oxygen atom as shown below:
$Molecular{\text{ }}mass{\text{ }}of{\text{ }}{H_2}O = (2 \times H) + (1 \times O) = (2 \times 1.00794) + (1 \times 15.9994) = 18.01528u$
Hence, the molecular weight of ${H_2}O$ is 18.01528u.

Note: Molecular mass plays a significant role in chemistry especially during setting up an experiment. During testing principles which involve specific amounts or quantities of a substance, molecular mass is used to figure out the exact quantity to be weighed of that particular substance. Basically molecular mass is used to determine the stoichiometry in the chemical reactions as well as equations.