Final answer:
The freezing point depression constant, Kf, is a characteristic of the solvent and its units are °C/m. It determines how much the freezing point of a solvent will decrease for every molal increase in solute concentration. For water, the value of Kf is 1.86°C kg.mol⁻¹.
Step-by-step explanation:
The freezing point depression constant, often represented as Kf, is a characteristic of the solvent, not the solution or solute. It's used in the calculation for the phenomenon where the presence of a solute lowers the freezing point of a solvent. The value of Kf depends on the type of solvent and can be found in various reference tables. For instance, water has a Kf of 1.86°C kg.mol⁻¹. The units of Kf are degrees Celsius per molality (usually expressed as °C/m).
The relationship between the freezing point depression (ΔTf) and the solute concentration is given by the equation ΔTf = mKf, where m is the molality of the solution. This shows that the freezing point depression is directly proportional to the molality of the solution and the molal freezing point depression constant of the solvent. An example often cited is the effect of dissolved NaCl compared to glucose; NaCl, dissociating into two particles, will have a more significant impact on the freezing point than glucose at the same molality.