Question

When 2.36g of a nonvolatile solute is dissolved in 100g of solvent, the largest change in freezing point will be achieved when the solvent is

A. paradichlorobenzene, kf=7.10.
B. water, Kf=1.86.
C. tert-butanol, Kf=9.1.
D All are expected to have the same freezing point.

Answer 1

The largest change in freezing point will be achieved when the solvent is tert-butanol, Kf=9.1.

Step-by-step explanation:

The largest change in freezing point will be achieved when the solvent is tert-butanol, Kf=9.1.

When a nonvolatile solute is dissolved in a solvent, the freezing point of the solvent is lowered. The extent of the freezing point depression depends on the molality of the solution and the molal freezing point depression constant of the solvent. The larger the molal freezing point depression constant, the larger the change in the freezing point.

In this case, tert-butanol has the highest molal freezing point depression constant, which means it will cause the largest change in the freezing point when a nonvolatile solute is dissolved in it.

Answer 2

Option c → Tert-butanol

Step-by-step explanation:

To solve this, you have to apply the concept of colligative property. In this case, freezing point depression.

The formula is:

ΔT = Kf . m . i

When we add particles of a certain solute, temperature of freezing of a solution will be lower thant the pure solvent.

i = Van't Hoff factor (ions particles that are dissolved in the solution)

At this case, the solute is nonvolatile, so i values 1.

ΔT = Difference between fussion T° of pure solvent - fussion T° of solution.

T° fussion paradichlorobenzene = 56 °C

T° fussion water = 0°

T° fussion tert-butanol = 25°

Water has the lowest fussion temperature and the paradichlorobenzene has the highest Kf. But the the terbutanol, has the highest Kf so this solvent will have the largest change in freezing point, when all the molalities are the same.