Molalität

Molality, symbolized by a lowercase 'm', is a measure of concentration in chemistry. It is defined as the amount of solute in moles divided by the mass of the solvent in kilograms. The formula for molality is m = moles of solute / kilograms of solvent. Unlike molarity, which is based on the volume of the solution, molality is based on the mass of the solvent. This distinction makes molality independent of temperature changes, as mass remains constant regardless of temperature.

For example, if you dissolve 1 mole of sodium chloride (NaCl) in 1 kilogram of water, the molality of the solution is 1 m. If you dissolve 0.5 moles of glucose in 500 grams (0.5 kg) of water, the molality is also 1 m. Molality is often used in colligative properties calculations, such as boiling point elevation and freezing point depression, because these properties are dependent on the number of solute particles in a given mass of solvent.

The units of molality are moles per kilogram (mol/kg). While molarity is more commonly encountered in general chemistry, molality finds its applications in more specialized areas of physical chemistry and thermodynamics where temperature independence is crucial. It is a robust measure of concentration that is unaffected by volume changes due to thermal expansion or contraction.