The freezing point of a substance is the temperature at which the solid and liquid forms are in equilibrium. To reattain equilibrium, the freezing point of the solute and solvent mixture is lowered relative to the original pure solvent.

32 °F.

∆Tf is negative because the temperature of the solution is lower than that of the pure solvent. Kf is the molal freezing point depression constant of the solvent (1.86 °C/m for water). m = molality = moles of solute per kilogram of solvent.

ΔTtrs , the change in phase transition point, which is always negative for freezing point depression and positive for boiling point elevation.

∆Tf is negative because the temperature of the solution is lower than that of the pure solvent. When determining changes in freezing point (or boiling point), solute concentration is usually not measured in molarity (moles of solute per liter of solution), but, rather, in molality.

Why is freezing-point depression a colligative property? It is directly proportional to the molal concentration (number of particles) of a solution. The change in the boiling point does not vary with the identity of the (solute, solvent), assuming all other factors remain constant.

Freezing point depression. The difference in temperature between the freezing point of a solution and that of it’s pure solvent.

Salt changes the freezing point of water, and causes the water to reach a lower temperature in order to freeze.

The freezing point of pure water is 0 °C (32 °F). How do you think adding salt to water affects its freezing point? Add salt will lower the freezing point and make it harder for the water to freeze. Gizmo Warm-up People often use salt to alter the freezing point of water.

The freezing point of the solvent in a solution changes as the concentration of the solute in the solution changes (but it does not depend on the identity of either the solvent or the solute(s) particles (kind, size or charge) in the solution).

The boiling point of a solvent will increase when a solute is dissolved in it. The elevation of the boiling point is directly dependent on the amount of solute present in the solution, but it is not based on the identity of the solute, so it is considered a colligative property.

Calcium chloride is more effective at melting ice because it can break down into three ions instead of two: one calcium ion and two chloride ions. More ions mean more ions getting in the way of those rigid ice bonds.

Hence the 0.2 M Na2SO4 has the lowest freezing point due to the highest moles of ions in solution.

freezing point of the solution is determined from the graph by drawing two straight lines through the data points above and below the freezing point. The temperature corresponding to the intersection of the two lines is the freezing point of the solution.

freezing point depression: The difference in temperature between the freezing point of the pure solvent and that of the solution. molal freezing-point depression constant: A constant that is equal to the change in the freezing point for a 1-molal solution of a nonvolatile molecular solute.