What is meant by ‘molecular mass’ in chemistry?

Molecular mass, in chemistry, refers specifically to the sum of the atomic masses of all atoms in a molecule. It provides a way to quantify the mass of a substance at the molecular level, which is essential for understanding its behavior in chemical reactions and calculations involving moles.

In this context, atomic mass is typically expressed in atomic mass units (amu), and when you sum these values for all the atoms present in a single molecule, you obtain the molecular mass. This concept is vital for stoichiometry, where accurate measurements of reactants and products in a chemical reaction are necessary.

Other options describe different concepts that do not pertain to the definition of molecular mass. For instance, the mass of a gas at standard temperature and pressure relates to gas laws and molar volumes but does not define molecular mass. Similarly, the weight of a mole of atoms in pure elements involves molar mass rather than the molecular mass of compounds. The mass ratio of liquid to solid states does not relate to molecular mass and instead concerns physical properties of states of matter.