Molality

Molality is the amount of solute, measured in moles, per kilogram of solvent. Because it uses solvent mass rather than solution volume, it does not change with temperature-driven expansion.

Amount of substance: A measure of how many specified entities, such as atoms or molecules, are present. Molality counts solute in moles, the SI unit for amount of substance.
Concentration: A measure of the amount of a constituent relative to a specified amount of mixture or medium. Molality is one concentration measure, defined using solvent mass.
Molar concentration: The amount of solute, in moles, per unit volume of solution. Unlike molality, it uses solution volume, which can vary with temperature.
Colligative properties: Solution properties determined by the number of dissolved particles rather than their chemical identity. Molality conveniently expresses particle concentration in several standard colligative-property equations.
Mole: The SI unit of amount of substance, equal to exactly 6.02214076 × 10²³ specified entities. The numerator of molality is the solute amount expressed in moles.
Mass: A physical property measuring the inertia of an object and its response to gravitational force. The solvent's mass determines molality's denominator and does not depend on thermal expansion.
Mass concentration: The mass of a constituent divided by the volume of the mixture containing it. It uses solute mass and solution volume rather than moles and solvent mass.
Boiling-point elevation: The increase in a solvent's boiling temperature caused by dissolved nonvolatile solute. Its ideal dilute-solution relation uses solute molality and the solvent's ebullioscopic constant.
Solute: A substance dissolved in a solvent to form a solution. Molality measures the amount of this component relative to the solvent's mass.
Temperature: A physical quantity that expresses how hot or cold a system is and governs thermal equilibrium. Changing temperature can expand solution volume without changing its molality.

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