Freezing point depression refers to the lowering of the freezing point of solvents upon the addition of solutes. It is a colligative property of solutions that is generally proportional to the molality of the added solute. The depression in the freezing point of a solution can be described by the following formula. ΔTf = i×Kf×m Where As per Raoult’s law, “the vapour pressure of a pure solvent decreases with the addition of a solute”. Since the vapour pressure of a non-volatile solvent is zero, the overall vapour pressure of the solution is lesser than that of the pure solvent. Why does the Freezing Point Depression Occur?The reason for the depression of the freezing point of a solvent upon the addition of a solute is explained below.
A graph detailing the freezing point depression of water upon the addition of sucrose to it is provided below. From the graph, it can be observed that the increase in the molality of sucrose causes further depression in the freezing point of the solvent (water). Freezing Point Examples
The normal freezing point and the corresponding freezing point depression is tabulated below.
Uses of Freezing Point DepressionSome important uses of freezing point depression are listed below.
Freezing point, when a liquid becomes a solid. Increased pressure, as with the melting point, typically increases the freezing point. Bringing a seed crystal into a supercooled liquid causes freezing, resulting in the release of fusion heat increasing the temperature to the freezing point rapidly.
Liquids have a temperature characteristic at which they become solids, known as their freezing point. Theoretically, a solid’s melting point should be the same as the liquid’s freezing point. During the action, it is possible to observe small differences between these quantities.
Fusion, vaporization and sublimation are endothermic processes, while exothermic processes are freezing, condensation, and deposition.
Water freezes when it hits 32 degrees Fahrenheit (0 degrees Celsius), but the amount of time it takes to do so depends on several variables that may vary from your neighbour’s in your freezer.
The six-phase changes are freezing, boiling, condensing, vaporizing, sublimating, and deposition. To learn more about this property of solutions and other colligative properties, such as the elevation in boiling point, register with BYJU’S and download the mobile application on your smartphone.
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0 arewrong out of 0 are correct out of0 are Unattempted View Quiz Answers and Analysis out ofAnswer Hint: By using the formula of depression in freezing point one can determine the relation between the freezing point and the molecular weight. The depression in freezing point is equal to the product of cryoscopic constant and molality. Complete step by step answer: The freezing point depression is explained as the lowering of the freezing point of the solvent with the addition of the solute.The freezing point depression is the colligative property which is proportional to the molality of the solute added.The freezing point depression is given by the formula as shown below.$\Delta {T_f} = {K_f} \times m$Where,$\Delta {T_f}$ is the freezing point depression${K_f}$ is the cryoscopic constantm is the molalityThe molality is defined as the number of moles of solutes dissolved in one kilogram of solvent.The formula of molality is shown below.$m = \dfrac{n}{{{M_1}}}$Where,m is the molalityn is the number of moles${M_1}$ is the mass in kilogramThe number of moles is given by the formula as shown below.$n = \dfrac{m}{{{M_2}}}$Where,n is the number of molesm is the mass${M_2}$ is the molecular weightSo, if we substitute the terms in the formula of freezing point depression then the new formula obtained will be.$ \Rightarrow \Delta {T_f} = {K_f} \times \dfrac{m}{{{M_2}{M_1}}}$If we keep the ${K_f}$, m and ${M_1}$ as constant then the freezing point depression will be inversely proportional to the molecular weight.$ \Rightarrow \Delta {T_f} = \dfrac{1}{{{M_2}}}$So, by increasing the value of depression in freezing point, the molecular weight decreases and vice versa.Thus, an increase in the molecular weight will have a smaller effect on the freezing point. Note: The freezing point is calculated by subtracting the depression in freezing point value and the freezing point of pure water which is zero degree Celsius. |