What are the meaning of the Terms Osmoles, Osmolarity and Osmolality.

One mole of osmotically active particles is called one osmole (osm).

Thus, a molar solution of glucose contains 1 osmole, a molar solution of NaCl contains 2 osmoles (1 mole of Na⁺ and 1 mole of CI ) while a molar solution of CaCl₂ contains 3 osmoles (1 mole of Ca²⁺and 2 moles of CI ).

The osmolar concentration of a solution (in osm/L) is called osmolarity. When expressed in osm/Kg of solution, it is called osmolality. Unlike osmolality, osmolarity is affected by temperature, which changes the volume of solution. Also, dissolution of solutes is associated with a slight rise in the volume of the solution. This increase is different for different solutes. Hence, when 1 mole of glucose is dissolved in 1 L of water, the osmolarity will be slightly less than 1 osm/L.