Question

1. A phenomenon called supercooling is frequently encountered in this experiment. In supercooling, a solution momentarily drops below its freezing point, and then warms up again, before solidification begins. What allows supercooling to occur?

2. The molal freezing point constant, Kf , is a property of the solvent, not the solute. The extent of freezing point depression on the other hand is a property of the solute. Explain why Kf is a property of the solvent and the extent of freezing point depression depends only on the amount of solute.

3. A phenomenon that happens sometimes during freezing point depression experiments is that the solute is affected in some manner by the solvent. One common occurrence is for a solute to dimerize, that is, two solute molecules combine to produce a single double molecule (a dimer). What effect would there be on a molar mass determination if the solute were to dimerize?

Answer 1

1. Supercooling is cooling the liquid below its freezing point without forming the solid. This happens with pure liquids without any particulate in it for crystal formation. Agistation is avided of the liquid. The liquids without any crystal point of specific size or seed fails to crystallize initially. Thus the liquid cools below the freezing point and any small particle formed in it redissolves by diffusion phenomenon.

2. Freezing point of solution is always less than the freezing point of the solvent which is a constant. a pure solvent always freezes at a particular temperature. Thus Kf is depedent only on the solvent and is a constant. When we add a solute, the freezing point is lowered and the extent of freezing point lowering is dependent upon the amount of solute present in the solution.

3. If the solute were to dimerize, the resulting molar mass calculation would be lower than the actual value as the decrease in freezing point would also be less.