Colligative Properties

A colligative property depends only on the number of solute particles and not on their nature. Osmotic pressure is the preferred colligative property for molar mass determination of macromolecules.
Step 1: Definition of Colligative Property Colligative properties are solution properties that depend only on the concentration of solute particles and not on their identity.

Examples of Colligative Properties: - Relative lowering of vapour pressure - Boiling point elevation - Freezing point depression - Osmotic pressure

Step 2: Why Osmotic Pressure is Preferred for Macromolecules? - Osmotic pressure ( ) is highly sensitive to small concentrations, making it ideal for determining the molar mass of macromolecules like proteins and polymers. - Unlike boiling point elevation or freezing point depression, osmotic pressure is measurable at room temperature, preventing thermal degradation of macromolecules.

Step 1: Understanding the problem. We are given that the solution is made with glucose, which is a non-volatile, non-electrolyte solute, and its molar mass is 180 g mol . We need to calculate the freezing point of this solution, given the boiling point elevation. The boiling point elevation formula is: Where: = Boiling point elevation = ebullioscopic constant (given as 0.512 K kg mol ) = molality of the solution

Step 2: Calculate the molality of the solution. The solution€™s boiling point is given as 100.20°C. The normal boiling point of water is 100°C, so: Using the boiling point elevation formula: Solving for molality:

Step 3: Calculate the freezing point depression. The freezing point depression formula is: Where: = Freezing point depression = cryoscopic constant (given as 1.86 K kg mol ) = molality of the solution (calculated as 0.3906 mol/kg) Substituting the values:

Step 4: Calculate the freezing point. The normal freezing point of water is 0°C. Since the solution has a freezing point depression, the freezing point of the solution will be: Thus, the freezing point of the solution is -0.726°C. \vspace{10pt}

(a) Cooking is faster in a pressure cooker than in an open pan: Cooking is faster in a pressure cooker because the pressure inside the cooker is higher than atmospheric pressure. This leads to an increase in the boiling point of water. As a result, the water in the cooker can reach a higher temperature before it boils, which speeds up the cooking process. In an open pan, the water boils at a lower temperature, so the food takes longer to cook.

(b) On mixing liquid X and liquid Y, volume of the resulting solution decreases: When mixing two liquids and the volume decreases, it indicates that there is an interaction between the molecules of liquid X and Y that causes them to pack more closely together, resulting in a decrease in the overall volume. This type of behavior shows a negative deviation from Raoult's law, which occurs when the intermolecular forces between the components of the mixture are stronger than the forces in the pure components.

(C) Change in temperature after mixing liquids X and Y: When a negative deviation occurs, the mixing of the liquids is usually exothermic, meaning it releases heat. As a result, the temperature of the solution would increase. This happens because the interaction between the molecules in the mixture is stronger than in the individual pure liquids, and energy is released when these interactions are formed. \vspace{10pt}

Step 1: Understanding association. In case of association, solute molecules aggregate, resulting in a reduction in the number of particles in the solution. This causes the molar mass to appear lower than the expected value.

Step 2: Conclusion. Thus, the abnormal molar mass decreases in case of association, corresponding to option (B). \vspace{10pt}