Colligative Properties of Electrolytes

Solutions of nonelectrolytes in water exhibit the colligative properties described in the preceding sections. These solutions also give, for the dissolved substances, the molar masses expected from their chemical formulae.

The study of colligative properties of electrolytes, however, requires a different approach than that used for the colligative properties of nonelectrolytes. The following are the experimental observations for the colligative behaviour of electrolytes:

i. The solutions of electrolytes also exhibit colligative properties, which do not obey the relations of nonelectrolytes.

ii. The colligative properties of the solutions of electrolytes are greater than those to be expected for solutions of nonelectrolytes of the same concentration.

iii. The molar masses of electrolytes in aqueous solutions, determined by colligative properties, are found to be considerably lower than the formula masses.

Why are the colligative properties of electrolyte solutions greater than those for nonelectrolyte solutions of the same concentration? Recall that electrolytes dissociate into two or more ions when dissolved in water, whereas nonelectrolytes do not. Stated differently, one formula unit of an electrolyte dissolved in water produces two or more ions. Consequently, the number of particles in solution increases. The colligative properties of electrolyte solutions are thus higher than those of nonelectrolyte solutions. …