Final answer:
To calculate the molecular weight, the molecular formula and the atomic masses of constituent atoms are needed. Multiplying the number of each atom in the molecule by its atomic mass and summing them gives the molecular weight.
Step-by-step explanation:
To calculate the molecular weight of a substance, you need to know the molecular formula of the substance and the atomic masses of the atoms that make up the molecule. The molecular formula tells you how many atoms of each element are in a molecule of the substance. You can then multiply the number of each type of atom by its respective atomic mass (usually given in atomic mass units, amu) and add all of these products together to obtain the molecular weight.
For example, to calculate the molecular mass of glucose, which has a molecular formula of C6H12O6, you would use the atomic masses of carbon (C), hydrogen (H), and oxygen (O) and add them up:
- (6 atoms of Carbon × atomic mass of Carbon) +
- (12 atoms of Hydrogen × atomic mass of Hydrogen) +
- (6 atoms of Oxygen × atomic mass of Oxygen).
Knowing the molecular weight helps in determining the number of moles and grams of the substance involved in chemical reactions and is crucial in stoichiometry.