The weight in atomic mass units of each of the atoms in a given formula is the molecular weight of a substance. An atomic mass unit is described as 1/12th the weight of the carbon-12 isotope. The old symbol was amu, while the most correct symbol is u (a lower-case letter u).
The molecular weight of a material is required to tell an individual how many grams there in one mole of that chemical substance. The mole is the typical method in chemistry for interacting as to how much of a substance is present.
Find out the molecular weight of Fe2O3?
Fe2O3 contains two atoms of iron and three atoms of oxygen
Mass of Iron = 55.847 amu
Mass of Oxygen = 15.9994 amu
Molecular weight of Fe2O3 is
Fe2O3 = 2 × 55.847 + 3 × 15.9994
Fe2O3 = 159.692 amu