Freezing Point Depression: Definition, Formula & Examples

Definition

• Freezing Point Depression: This is a colligative property where the freezing point of a pure solvent is lowered by the addition of a solute.
  • Colligative Property: Depends on the number of solute particles, not their identity.
  • Measured using molarity (mol/L) or molality (mol/kg).
  • Adding solute affects the formation of the lattice structure necessary for freezing, requiring more energy removal, thus lowering the freezing point.

Key Concepts

• Freezing Point: Temperature where a solution changes from a liquid to a solid.
• Example: Liquid X with a 4.2°C freezing point changes to 2.7°C when Solute Y is added, indicating a freezing point depression of -1.5°C.

Real-World Example

• Oceans remain liquid while freshwater sources freeze due to salt in the ocean water, causing a freezing point depression of approximately 2°C.

Formula

• Freezing Point Depression Equation: ΔT = i * Kf * m
  • ΔT: Change in freezing point.
  • i: van’t Hoff factor (degree of ionization of solute).
  • Kf: Freezing point depression constant, specific to each solvent.
  • m: Molality of the solution.

FAQs

• Freezing Point vs. Freezing Point Depression:
  • Freezing Point: Temperature at which liquid becomes solid.
  • Freezing Point Depression: Lowering of this temperature due to solute addition.
• Freezing Point Equation: Not applicable since it is a measurable temperature.
• Freezing Point Depression Constant (Kf): Experimentally determined for each solvent.

Additional Resources

• Topics related to colligative properties like Boiling Point Elevation are covered in other lessons.

This summary provides a high-level overview of the concept of freezing point depression, its calculation, and real-world implications. For an in-depth study, students are encouraged to access the full course material and related lessons on Study.com.