CHEM FINAL
Chapter 11 (Theory) Section 11.4-11.5 [1 question]
4.1 Colligative Properties Overview
Nature of Solutions: Solutions have different properties than their constituent pure solute
and solvent.
Dependent Properties: Some properties of solutions like acidity, basicity, and density
depend on the specific identity of the solute.
Colligative Properties: These are specific properties that depend primarily on the
concentration of solute particles rather than the nature or identity of the solute itself.
Colligative Properties Discussed:
Vapor Pressure Lowering:
Definition: When a non-volatile solute is dissolved in a solvent, it results in the lowering of
the vapor pressure of the solvent. This occurs because the solute molecules occupy space at
the surface of the solution, thereby reducing the number of solvent molecules that can
escape into the vapor phase.
Units: The change in vapor pressure (ΔP) is measured in atmospheres (atm), millimeters of
mercury (mmHg), or pascals (Pa).
Boiling Point Elevation:
Definition: The boiling point of a solution is higher than that of the pure solvent. This
elevation in boiling point occurs because the presence of solute particles lowers the
solvent's vapor pressure, requiring a higher temperature to reach the boiling point where
the vapor pressure equals atmospheric pressure.
Units: The change in boiling point (ΔT_b) is typically measured in degrees Celsius (°C) or
Kelvin (K).
Freezing Point Depression:
Definition: The freezing point of a solution is lower than that of the pure solvent. This
depression in freezing point can be explained by the disruption of the solvent’s crystal
lattice formation by solute particles, requiring a lower temperature to solidify.
