Molar mass is the mass (in atomic mass units) of one mole of a substance. The molecular weight of a molecule is the total number of protons and neutrons in all the atoms in that molecule. The boiling point of a solution of an involatile solute is higher than that of the pure solvent, and the boiling-point elevation (DeltaT) is directly proportional to the amount concentration for dilute solutions. When the amount concentration is expressed as a molality, the proportionality constant is known as the ebullioscopic constant (Kb) and is characteristic for each solvent. If w represents the mass fraction of the solute in solution, and assuming no dissociation of the solute, the molar mass is given by the formula.