Freezing Point Depression and Colligative Properties Quiz

Freezing Point Depression

• Freezing point depression is a colligative property observed in solutions that results from the introduction of solute molecules to a solvent.
• The freezing points of solutions are all lower than that of the pure solvent.
• The freezing point depression is directly proportional to the molality of the solute.
• The freezing point depression equation is: ΔT_f = T_f(solvent) - T_f(solution) = K_f × m
• Where ΔT_f is the freezing point depression, T_f(solvent) is the freezing point of the solvent, T_f(solution) is the freezing point of the solution, K_f is the freezing point depression constant, and m is the molality.

Types of Solutes

• Nonelectrolytes are substances with no ions, only molecules.
• Strong electrolytes are composed mostly of ionic compounds and essentially all soluble ionic compounds form electrolytes.

Solving Problems

• If the substance is uniform and not ionic, it can be assumed to be a nonelectrolyte and the formulas can be used to solve problems.
• These equations work for both volatile and nonvolatile solutions.
• The vapor pressure does not affect the change in temperature.

Colligative Properties

• Adding solutes to an ideal solution results in a positive ΔS, an increase in entropy.
• The properties that undergo changes due to the addition of solutes to a solvent are known as colligative properties.
• Colligative properties are dependent on the number of solutes added, not on their identity.
• Examples of colligative properties are boiling point and freezing point.

Boiling Point Elevation and Freezing Point Depression

• The boiling point and freezing point of a pure solvent can be changed when added to a solution.
• The freezing point of the pure solvent may become lower, and the boiling point may become higher.
• The extent to which these changes occur can be found using the formulas: ΔT_f = -K_f × m and ΔT_b = K_b × m.

Conditions for Colligative Properties

• The solute must fulfill two conditions to exert a change on colligative properties: it must not contribute to the vapor pressure of the solution, and it must remain suspended in the solution even during phase changes.

Chemical Potential

• The chemical potential of the solvent is lower when solutes are added.
• Chemical potential is the molar Gibb's energy that one mole of solvent is able to contribute to a mixture.
• The higher the chemical potential of a solvent is, the more it is able to drive the reaction forward.