Electrolytes: van't Hoff Factor

Colligative properties of a solution depend on the actual number of dissolved solute particles.

For a non-electrolyte, each solute molecule that dissolves yields one dissolved solute molecule.

However, ionic electrolytes, such as sodium chloride, dissociate into ions when dissolved, while ammonia gas, a covalent electrolyte, reacts with water to release ammonium and hydroxide ions in solution.

So for electrolytes, each solute molecule that dissolves yields more than one dissolved solute particle.

Thus, a 1 M solution of a non-electrolyte such as dextrose, will have 1 mole of dextrose molecules in a 1-liter solution, whereas a 1 M solution of an electrolyte such as potassium chloride will dissociate into nearly 1 mole of potassium ions and 1 mole of chloride ions-- a total of 2 moles of ions in a 1-liter solution.

With double the number of solute particles, the osmotic pressure of a 1 M potassium chloride solution will be twice that of a 1 M dextrose solution.

The ratio between the moles of particles that a dissolving solute forms in solution and the moles of solute added to make a solution, is called the van’t Hoff factor represented by i.

It is calculated by dividing the measured