In chemistry, the
osmole (
Osm or
osmol) is a non-
SI unit of measurement that defines the number of
moles of solute that contribute to the
osmotic pressure of a
solution. The term comes from the phenomenon of
osmosis, and is typically used for osmotically active solutions. For example, a solution of 1 mol/L NaCl corresponds to an osmolarity of 2 osmol/L. The NaCl salt particle dissociates fully in water to become two separate particles: an Na
+ ion and a Cl
- ion. Therefore, each mole of NaCl becomes two osmoles in solution, one mole of Na
+ and one mole of Cl
-. Similarly, a solution of 1 mol/L CaCl
2, gives a solution of 3 osmol/L (Ca
2+ and 2 Cl
-).