Final answer:
Freezing point depression is the lowering of a solvent's freezing point due to the addition of a solute. The freezing point depression constant (Kf) is used in calculating the difference in freezing points (ΔTf = Kf * m) between the pure solvent and the solution. The van't Hoff factor is applied to find the effective concentration impacting the freezing point depression.
Step-by-step explanation:
The phenomenon of freezing point depression refers to the effect where the freezing point of a solvent decreases when a solute is dissolved in it. This lowering of the freezing point occurs because the solute particles disrupt the formation of the solvent's solid crystal structure, requiring a lower temperature to achieve solidification. For instance, when salt is added to icy roads, it prevents water from freezing at 0°C and allows it to remain liquid at temperatures as low as −9°C. The freezing point depression constant, often symbolized as Kf, is a unique property for every solvent and is used in the calculation (ΔTf) which is the change in freezing point. The equation to calculate the freezing point depression (ΔTf) is ΔTf = Kf * m, where 'm' stands for the molality of the solution.
To obtain the effective concentration of solute particles (which affects the freezing point depression), the van't Hoff factor (i) is used, which takes into account the dissociation of solute particles in a solution. By multiplying the van't Hoff factor by the molality, you get the effective concentration. The greater this effective concentration, the more significant the freezing point depression will be.