Compare the concepts of molecular weight and relative molecular weight.

Molecular weight is the mass of a molecule of a substance. This value is too small, within 10-23 – 10-21 degrees, so it is inconvenient to use it in calculations.
To facilitate calculations, the concept of relative atomic mass was invented. The relative atomic mass is 1/12 the mass of a carbon atom (1.66 * 10-24 grams). The masses of all chemical elements are converted to this unit and their values ​​can be found in the periodic table.
Summing up the relative masses of atoms of all the elements that make up the molecule, you can get the value of the relative molecular weight.
For example, the mass of a water molecule (H2O) is 2.99 * 10 ^ 23g, and the relative molecular weight is M (H2O) = 2 + 16 = 18g.