Purpose: The purpose of this lab is to learn how to determine the molecular weight of a compound by measuring the freezing point depression.

Background: In this lab, the freezing point depression of the lauric acid and the lauric acid of the unknown are graphed. This makes it possible to calculate the formula weight of the unknown and therefore identify the unknown. We predicted that adding a solute to a pure solvent would decrease the freezing point. The importance of this lab was to be able to use freezing point depression to find the molecular weight of a substance. Understanding the process by which solutions are made helps one understand colligative properties. Colligative properties include vapor pressure, freezing point depression, and boiling point elevation. Bonds in the solute and solvent have to be broken in order to accommodate the dissolved particles, which requires energy. The solute and solvent are then available to form bonds with each other and energy is released. A positive energy change int he heat of solution indicates an endothermic solution process while a negative enegry change indicates an exothermic process. Because of the bonds formed between the solute and solvent molecules, a solution has fewer available solvent molecules available to escape from the liquid phase into the gas phase and thus the vapor of the solvent builds a lower vapor pressure over the solution.