Colligative properties are properties of solutions that depend on the concentration of solute particles, but not on the identity of the solute. These properties include boiling point elevation, freezing point depression, osmotic pressure, and vapor pressure lowering.
In a colligative properties lab, students may be asked to measure the boiling point elevation or freezing point depression of a solution and compare it to the expected value calculated using the appropriate colligative property equation. For example, to measure the boiling point elevation of a solution, a student may prepare several solutions of different concentrations and use a thermometer to measure the boiling point of each solution. The student can then compare the measured boiling points to the expected values calculated using the equation for boiling point elevation, which is:
ΔTb = Kb * molality
Where ΔTb is the boiling point elevation, Kb is the boiling point elevation constant for the solvent, and molality is the concentration of the solute in molality (moles solute per kilogram solvent).
Another common colligative property experiment involves measuring the osmotic pressure of a solution. Osmotic pressure is the pressure that must be applied to a solution to prevent the flow of solvent into the solution across a semi-permeable membrane. To measure osmotic pressure, a student may prepare several solutions of different concentrations and use a manometer to measure the pressure required to prevent the flow of solvent into the solution. The student can then compare the measured osmotic pressure to the expected value calculated using the equation for osmotic pressure, which is:
Π = M * R * T
Where Π is the osmotic pressure, M is the concentration of the solute in moles per liter, R is the ideal gas constant, and T is the temperature in kelvin.
In addition to measuring colligative properties, a colligative properties lab may also include an investigation of the relationship between colligative properties and molality. For example, students may be asked to plot the boiling point elevation or freezing point depression of a solution as a function of molality and observe the linear relationship between these properties.
Overall, a colligative properties lab provides students with the opportunity to explore the properties of solutions and understand how they are affected by the concentration of solute particles. This understanding is important for a variety of applications, including the purification of substances, the formulation of medications, and the design of industrial processes.