Question

How to calculate relative molecular mass?

Answer 1

Hint : Molecular mass of a compound is known as the mass of one molecule. Molecular mass differs because of the isotopes. The unit of molecular mass is measured in $amu$ . Amu stands for atomic mass units.

Complete Step By Step Answer:
The Relative Molecular Mass ( ${M_r}$ ) is the sum of the Relative Atomic Mass ( ${A_r}$ ) of each atom in the molecule.
Relative molecular mass of a molecule is also defined as the average mass of one molecule of a substance when compared with $\dfrac{1}{{12}}$ of the mass of an atom of carbon $- 12$ or compared with one normal hydrogen atom.
The formula is as follows:
Relative molecular mass of a molecule = \dfrac{\text{Average mass of one molecule of a substance}}{\text{mass of dfrac{1}{{12}} $of an atom of carbon$ - 12 }}
For example, let us calculate the relative molecular mass of $NaCl$ ,
Relative molecular mass of $NaCl =$ $1$ molecule of $Na$ $+ 1$ molecule of $Cl$
Relative molecular mass of $NaCl$ $= 1 \times 23 + 1 \times 35.5$
Relative molecular mass of $NaCl$ $= 58.5$
It is represented by the symbol $M$ .It has no units.
It is known as the sum of relative atomic masses of all the atoms in the molecule.
Molecular mass of the molecule can be controlled in three ways: Mass spectrometry, hydrodynamic strategy, Static light scattering.

Note :
Relative molar mass and molar mass are different from each other but are related to each other. Molecular mass is known as the mass of a molecule of a substance. It is also known as Molecular weight. Molar mass is the mass of $1$ mole of a substance or Avogadro's number of the molecules of that substance.