Colligative Properties Lab

The calculations for colligative properties do not depend on the identity of a substance that is being used because only the amount of the substance that is used plays a role. The types of calculations that are colligative properties are: freezing point of depression, boiling point elevation, vapor pressure lowering, and osmotic pressure.1 Colligative properties are present in everyday life, such as adding salt to a boiling pot of water. By adding salt to the water, the boiling point of elevation is raised and the boiling salt water will have a higher temperature compared to the temperature of boiling pure water.2 The colligative property that will be used in this experiment is the freezing point of depression, which can be calculated using the equation:
∆T_f= k_f × m × i
In the equation the kf stands for the freezing point of depression constant for a given solvent, m stands for the molality (mol solute/kg solvent) of the solute, and i stands for the van’t Hoff factor of the solute. In this experiment, the freezing point of depression will be calculated for two unknown solutions in order to determine the molecular weights and identities of the unknowns.
Experimental
For Part A of this experiment, an ice and salt bath was prepared by first filling a 150mL beaker full of ice and weighing out approximately
However, the weight of the sample was 4.692g instead of 2.649g and the van’t Hoff factor used was 1 and not 2. Using this method, the “theoretical” freezing point came out to be 1.274oC. This “theoretical” freezing point was then compared to the “corrected” freezing point by calculating the percent error, using the same equation as before. Using the formula and the value of the “correct” freezing point found in Part D of the experiment, the percent error came out to be