Osmolarity

Osmolarity is a measure of solute concentration, as defined by the number of osmoles of a solute per litre of solution (osmol/L)

Solutions may be loosely categorised as hypertonic, hypotonic or isotonic according to their relative osmolarity

• Solutions with a relatively higher osmolarity are categorised as hypertonic (high solute concentration ⇒ gains water)
• Solutions with a relatively lower osmolarity are categorised as hypotonic (low solute concentration ⇒ loses water)
• Solutions that have the same osmolarity are categorised as isotonic (same solute concentration ⇒ no net water flow)