Depression in freezing point class 12

Solution Elevation of Boiling Point Boiling point of a solution is always higher than that of the pure solvent. For dilute solutions, elevation of boiling point is directly proportional to the molar concentration of solute in a solution. `ΔT_b∝m` Or, `ΔT_b=K_bm` Here, m is molality and K b is called Boiling Point Elevation Constant or Molal Elevation Constant (Ebullioscopic Constant). The unit of K b is K kg mol -1 If w 2 g of solute of molar mass M 2 is dissolved in w 1 g of solvent. Then molality of solution is given as follows: `m=((w_2)/(M_2))/((w_1)/(1000))-(1000xx\w_2)/(M_2xx\w_1)` Substituting the value of molality in previous equation we get: `ΔT_b=(K_b\xx1000xx\w_2)/(M_2xx\w_1)` Or, `M_2=(1000xx\w_2xx\K_b)/(ΔT_b\xx\w_1)` Example: 18 g of glucose C 6H 12O 6 is dissolved in 1 kg of water in a saucepan. At what temperature will water boil at 1.013 bar? K b for water is 0.52 K kg mol -1. Answer: Moles of glucose `=(18g)/(180g\text(mol)^(-1))=0.1` mol Mass of solvent = 1 kg Hence, molality of glucose solutin = 0.1 mol kg -1 For water, change in boiling point Δ `T_b=K_b\xx\m` `=0.52K\kg\text(mol)^(-1)xx0.1text(mol)kg^(-1)=0.052` K Boiling point of water at 1.013 bar is 373.15 K So, boiling point of solution `= 373.15 + 0.052 = 373.202` K Example: The boiling point of benzene is 353.23 K. When 1.80 g of a non-volatile solute was dissolved in 90 g of benzene, the boiling point is raised to 354.11 K. Calculate the molar mass of the solute. K b for benzene is 2.53 K kg mol ...

Hint: The temperature at which the liquid turns into a solid at normal atmospheric pressure is known as the freezing point. The decrease in the freezing point of a solvent when a non-volatile solute is added to it is known as the depression in the freezing point of the solvent. Complete step by step answer: When any solute is added to a solvent the attraction between the liquid particles is hindered. As the attractions decrease, the freezing point decreases. At the freezing point, the liquid and solid phases of a substance are in equilibrium with each other. Thus, at the freezing point, the liquid solvent and a form of solid solvent are in equilibrium. Thus, during depression of freezing point in a solution, liquid solvent and solid solvent are in equilibrium. Thus, the correct option is option (A). Additional Information: The property of any solution which depends on the concentration of the molecules or ions of the solute is known as a colligative property. The depression in freezing point is one such colligative property. Other colligative properties are: lowering in vapour pressure, elevation in boiling point and osmotic pressure. The depression in freezing point decreases the freezing point of the pure solvent. Thus, when a solute is added to a pure solvent, the freezing point of the pure solvent decreases. Thus, the freezing point of a solution is always lower than the freezing point of the pure solvent. Note: Remember that there is depression in the freezing point o...

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Depression in Freezing Point of a Solution: Can you make your ownice cream in a baggie without a refrigerator? Yes, we can. Just add salt to the ice; the mixture becomes so cold that it can give frostbite if held for long. Why does it happen so? Is it similar to adding salt to the water? Let’s find out more about it in this article. The salt and ice mixture is quite cold because it follows a basic scientific principle. This principle is one of the colligative properties of a solution that depends on the number of solute particles present in the solution. The depression in the freezing point of a solutionis a consequence of adding a non-volatile solute to the solvent. What is Depression in the Freezing Point of a Solution? At normal atmospheric pressure, the temperature at which a liquid becomes a solid is known as the freezing point of a liquid. In simple words, it is the temperature at which liquid and solid phases of a substance coexist in equilibrium. A solution will freeze when its vapour pressure equals the vapour pressure of the pure solid solvent. When a non-volatile solute is added to a volatile liquid solvent, the vapour pressure of the resulting solution becomes lower than that of the pure solvent. Hence, the temperature required by the liquid solvent to reach its solid state is lowered. This results in the Depression of the freezing point of the solution compared to the solvent. The difference in temperature between the freezing point of the pure solvent and tha...

The difference between the freezing point of the pure and the solution containing the involatile solute is called the depression of freezing point. The freezing point is a point where the chemical potential of its liquid and solid phases is equal. It is colligative property because it depends only on the amount of the solute added to a given solvent. If T o is the freezing point of a pure solvent, T f is the freezing point of the solution, then the freezing point of depression T f is given by: T o– T f = ΔT f Depression of Freezing Point Graph Let us consider the freezing of a pure liquid solvent. As its freezing point equilibrium exists between solid and liquid, and the escaping tendencies in the two phases are identical, i.e., the vapor pressure of the solid phase and liquid phase are similar in their chemical potentials. But, as the involatile solute is added to the liquid phase, the proportion of molecules bouncing against the solid phase decreases. The escaping tendency of solvent molecules from liquid to solid has been diminished, whereas the reverse escaping tendency (solid to liquid) is unaffected and crystals of solvent begin to dissolve. To prevent this and restore equilibrium, we must favor the solid phase by lowering the temperature. At some lower temperature, the two escaping tendencies again match, and equilibrium is attained. Thus, this implies that on the addition of solute to the solution, the freezing point can be lowered. Molal Freezing Point Depression ...