What does molal mean?
Molal is an adjective used in chemistry for measurements based on molality. A molal concentration expresses the amount of solute in moles per kilogram of solvent, rather than per liter of solution. This distinction matters because a solution's volume can change with temperature, while the mass of its solvent remains more stable. Molal quantities are therefore especially useful when studying properties that depend on the number of dissolved particles, such as freezing-point depression, boiling-point elevation, and osmotic pressure. Although molal is closely related to the more familiar word molar, the two terms are not interchangeable: molal refers to a solvent-mass basis, whereas molar refers to a solution-volume basis. Molal is primarily technical vocabulary found in chemistry textbooks, laboratory contexts, and scientific discussion.
adjectiveRelating to molality or molal concentration, especially the concentration of a solution measured in moles of solute per kilogram of solvent.
- Relating to or denoting molality or molal concentration.
"The chemist calculated the molal concentration of the solution before determining its freezing point."
"The solution's molal concentration was used to calculate its freezing-point depression."
"In discussions of colligative properties, a molal quantity is often preferred because it does not change when the solution expands."
Molal chemistry counts molecules per kilogram of solvent, not per liter of solution.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does molal come from?
Molal was formed within chemistry from mole, the unit used to measure an amount of substance, together with the suffix -al. Its related vocabulary—mole, molecular, molecule, and molar—ultimately connects with Latin moles, meaning a large mass or bulk. In modern usage, molal specifically refers to concentration measured by the mass of solvent.
Related word forms
How molal is actually used
This is specialized chemistry terminology. It is less common in general use than molar and is often encountered in discussions of colligative properties, osmotic pressure, and freezing-point depression.
Easily confused with molal
Molal describes a concentration based on the mass of solvent, while molar describes a concentration based on the volume of the solution.