When a solution is formed, it is characterized by four main properties, known as colligative properties: vapor pressure, boiling point, freezing point and osmotic pressure. Solutes added to a solvent create a solution that is different from the original solvent. Collectively, the colligative properties of a solution give a holistic view of the solution’s behaviors and characteristics.
The term "colligative properties" is applied to solutions composed of a solute that is considered “nonvolatile." This essentially means that it has a low vapor pressure. In addition, these properties depend only on the number of particles in a specified amount of solution. When a solute is added to a nonvolatile solvent, the vapor pressure is lower than it is in the original solvent. The boiling point of a solution is thus higher than the original solvent, because the vapor pressure must be equal to the atmospheric pressure for a substance to boil. On the other hand, the freezing or melting point is lower for a solution than it is for the solvent. The final colligative property is osmotic pressure. If the solution and the solvent are separated by a semi-permeable membrane, the solvent will naturally flow through the membrane into the solution to become more diluted. This is because the solvent has a higher chemical potential than does the solution.