So remember, for the colligative properties, the more solute you add, the more they can be affected. Boiling point and osmotic pressure will keep going up, freezing point and vapor pressure will go down. Now the solute amount added equals the number of ions of that solute, well, remember that the van't Hoff factor, so that's I, times the concentration of that compound or solute. Now this concentration could represent either molarity or molality, and if we're incorporating ions with molarity or molality, then they become osmolarity and osmolality. So remember, osmolarity is ionic molarity, osmolality is ionic molality. Alright.
So for osmolarity, solute formula, we're going to say osmolarity, which is the amount of solute, equals I, the number of ions for the solute, times the molarity of the compound as a whole. Osmolality is the same kind of idea. It equals I, the number of solute ions that we have, times the molality of the compound. These two formulas will help us determine the amount of solute that a solute given to us represents. And that'll help us determine which one will have the highest boiling point or which one will have the lowest freezing point, etcetera. So keep this in mind. We use osmolarity and osmolality to determine the amount of solute that is.