Question

Depression of freezing point of which of the following solutions does represent the cryoscopic constant of water?

• A. 6% by mass of urea in aqueous solution.
• B. 100 g of aqueous solution containing 18 g of glucose.
• C. 59 g of aqueous solution containing 9 g of glucose.
• D. 1 M $KCl$ solution in water.

Answer 1

Answer: (C)

59 g of aqueous solution containing 9 g of glucose.

For a solution having unit molality of normal solutes, the cryoscopic constant is equal to the depression in freezing point $(K_f=\Delta T_f)$.
59 g of aqueous solution containing 9 g of glucose has molality $\frac{9\times 1000}{(59-9)\times 180}=1$.
Hence, the depression of freezing point of aqueous solution containing 9 g of glucose does represent the cryoscopic constant of water?