Question

The solution from the following with highest depression in freezing point/lowest freezing point is

• A. 180 g of benzoic acid dissolved in benzene
• B. 180 g of acetic acid dissolved in benzene
• C. 180 g of acetic acid dissolved in water
• D. 180 g of glucose dissolved in water

Answer 1

Answer: (C)

180 g of acetic acid dissolved in water

Answer 2

To determine which solution has the highest depression in freezing point, we need to consider the colligative properties of solutions, specifically the freezing point depression.

Colligative Properties: Freezing point depression is given by the formula:

ΔTf = i · Kf · m

where ΔTf is the depression in freezing point, i is the van 't Hoff factor (number of particles the solute breaks into), Kf is the cryoscopic constant of the solvent, and m is the molality of the solution.

Analyzing Each Option:

• Option (3): 180 g of acetic acid in water. Acetic acid partially ionizes in water (i ≈ 1). The molality will be relatively high as the solvent is water.
• Option (2): 180 g of acetic acid in benzene. Acetic acid does not ionize in benzene (i = 1). Benzene has a lower Kf than water, leading to a lesser depression.
• Option (1): 180 g of benzoic acid in benzene. Similar to option (2), it does not ionize, and its effect will be limited by benzene’s lower Kf.
• Option (4): 180 g of glucose in water. Glucose does not ionize (i = 1), but its molar mass is higher, leading to a lower molality compared to acetic acid.

Conclusion: Given that acetic acid has a higher molar mass than glucose and ionizes in water, it will result in a greater freezing point depression.

Thus, the solution with the highest depression in freezing point is: 180 g of acetic acid dissolved in water.