molmassan

Molmassan, commonly referred to as the molar mass, is the mass of one mole of a substance. It expresses how much matter a mole of the substance contains and is typically given in grams per mole (g/mol). The molmassan is calculated by summing the contributions of all atoms in the formula of the substance, weighted by their quantities.

For a compound, the molar mass is M = Σ (a_i × M_i), where a_i is the number of atoms of element i in the formula unit and M_i is the molar mass of that element (in g/mol). For a pure element, the molar mass equals the element’s standard atomic weight expressed in g/mol. In practice, M_i reflects the isotopic composition of the element as used in standard references.

Isotopic variation and hydration can affect the molmassan. If a compound contains water of crystallization or other ligands, their masses must be included. When precise work is required, the exact isotopic composition of each element and the state of hydration are taken into account.

The molar mass is fundamental for converting between mass and amount in moles, enabling stoichiometric calculations in chemical reactions. It is related to the dimensionless relative atomic mass (atomic weight) but expressed with units, typically g/mol, making it convenient for laboratory measurements and reactions.

Examples: water (H2O) has a molmassan of about 18.015 g/mol; glucose (C6H12O6) is approximately 180.156 g/mol.