Question

Which of the following liquids will have the lowest freezing point?

A. aqueous LiF (0.65 m)
B. Pure `H_2O`
C. aqueous sucrose (0.75 m)
D. aqueous `CdI_2` (0.39 m)
E: aqueous glucose (0.75 m)

Thanks in advance

Answer 1

It should be D as the true answer, but if we ignore the impossible concentration of LiF, the intended answer is probably A.

Explanation:

According to colligative properties of solutes, depression of freezing point follows the number of particles produced upon solubilization. It depends on the concentration of `CdI_2`, which is 0.39 molal.

Theoretically `CdI_2` giving three ions per formula when dissolved in water, should give the second highest freezing depression, at that concentration.

On the other hand `LiF` is actually sparingly soluble in water (about 0.071 M), and cannot be dissolved at 0.65 molal.

So the answer depends on whether we want to represent physical reality or answer a theoretical question. [Sucrose and glucose give only one particle per molecule.]