3.1: Background

Colligative properties are defined as solution properties that depend solely on the concentration of the solute particles, not their identity. These properties include changes in boiling point, freezing point, vapor pressure and osmotic pressure. For instance, magnesium chloride and calcium chloride both lower the freezing point of water to -20°C despite having different chemical identities.

We can define the change in colligative properties of a solution based on the following equations with constants in reference to the solvent:

We can use colligative property changes as a tool to help us determine the identity of a compound, such as whether it is an electrolyte or not, or even the number of ions produced when a solute is dissolved in a solvent. You will be using colligative properties, along with other tests performed in this class and general chemistry I, to determine the identity of an unknown substance found at a crime scene.

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