Question

FeCl₃ has a van't Hoff factor of 3.4. What is the freezing point (in °C) of an aqueous solution made with 0.81 m FeCl₃? (Kf for water is 1.86 °C/m)

a. -4.02°C
b. -2.16°C
c. -7.50°C
d. -11.34°C

Answer 1

The freezing point of a 0.81 m aqueous solution of FeCl3, with a van't Hoff factor of 3.4, is calculated to be -5.12°C by using the freezing point depression formula. This calculated value does not match any of the provided options, suggesting a possible error.

Step-by-step explanation:

The student asked what the freezing point of an aqueous solution made with 0.81 m FeCl3 is, given that FeCl3 has a van't Hoff factor of 3.4 and the Kf for water is 1.86 °C/m.

To solve this problem, we apply the formula for freezing point depression using the van't Hoff factor (i), which is ΔTf = i × Kf × m. Plugging in the values, we have ΔTf = 3.4 × 1.86 °C/m × 0.81 m. Calculating this, we get a freezing point depression of ΔTf = 5.12 °C.

Since the normal freezing point of water is 0 °C, we subtract the depression value from 0 °C to find the new freezing point, which will be -5.12 °C. Therefore, the closest answer to the calculated value is -5.12°C, which is not listed among the options provided. It seems there might be a mistake in the options given or in the question itself.