Final answer:
Osmolarity is defined as the molarity of a solute times the number of particles it dissociates into when dissolved in a solution. It is important for calculating osmotic pressure in solutions.
Step-by-step explanation:
Osmolarity (Osm) is defined as the molarity of a solute times the number of particles a formula unit of the solute makes when it dissolves (represented by i):
osmol = M x i
This means that osmolarity considers not just the concentration of a solution in terms of molarity, which is the number of moles of solute per liter of solvent, but also accounts for the number of particles into which a solute dissociates in solution. For instance, NaCl dissociates into two particles, Na+ and Cl-, so i would be 2 for NaCl. Therefore, if the molarity of a NaCl solution is 1 M, the osmolarity would be 1 M x 2, or 2 Osm.