Question

Calculate the molecular mass of $N{{H}_{3}}$.

Answer 1

Hint: Molecular mass is generally represented by m and it is the mass of a given molecule. Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. Isotopes are those compounds which have the same number of protons but different numbers of neutrons.

Complete answer:
The molecular weight of substance is defined as the weight in atomic mass units of each of the atoms in a given formula where an atomic mass unit is described as 1/12th the weight of the carbon-12 isotope. The molecular weight of a material is required to tell an individual how many grams there is in one mole of that chemical substance i.e. molecular weight of any substance contains 1 mole of that substance.
Molecular mass of any compound can be calculated by adding up the molecular mass of all the compounds present in it. Here ammonia is given which we know is composed of nitrogen and three hydrogen molecules. We know that the molecular mass of nitrogen is 14 and of hydrogen is 1. Molecular formula of $N{{H}_{3}}$ is calculated as follows:
$N{{H}_{3}}=1\times 14+3\times 1=17$g
Hence the molecular mass of $N{{H}_{3}}=1\times 14+3\times 1=17$is 17 gm.

Note:
The molecular mass of small and medium size molecules can be measured with the help of mass spectrometry and also used to determine the composition of elements in the molecule. The molecular masses of macromolecules like proteins can also be determined by mass spectrometry.