What is molecular weight? How is it calculated?

Molecular weight is the mass of one molecule of a given substance. In order to determine it, you need to know the chemical formula of a substance. For example, for water, this formula is H₂O. According to the periodic table, we determine the atomic mass of hydrogen Аr (Н) ≈ 1 amu, the atomic mass of oxygen Аr (О) ≈ 16 amu, then the water molecule will have the mass Мr (Н₂О) = 2 ∙ Аr (H) + Ar (O) = 2 ∙ 1 amu + 16 amu = 18 amu
Since the relative unit of mass is 1 amu. = Аr (С) / 12 = 1.66 ∙ 10 (- 27) kg, then the mass of a water molecule will be: m₀ = 18 ∙ 1.66 ∙ 10 ^ (- 27) kg = 29.88 ∙ 10 ^ (- 27 ) kg.