Can you please explain the difference between osmolarity and osmolality?
2nd December 1998 There is no difference! Osmolarity tends to be the preferred term here in the UK, but both words are in common use in the literature. They are both derived by multiplying together the molarity of a solution and the number of particles into which each molecule of the solute dissociates in solution. So, in the case of glucose which does not dissociate in solution, a one molar solution (180 grams of glucose dissolved in one litre of solution) has an osmolarity of one osmole. On the other hand, when sodium chloride molecules dissolve in solution they dissociate into two ions – a sodium ion and a chloride ion – and so a one molar solution (58.5 grams dissolved in one litre of solution) has an osmolarity of two osmoles. The significance of this stems from the way that osmotic pressure is generated by the number of solute particles in a solution, not so much their size or chemistry. Thus, the greater the number of particles into which a substance dissociates, the greater the
