Question

Which solution has the highest freezing point?

O a solution formed by dissolving 0.75 mol of KCl in 1.00 kg of water
O a solution formed by dissolving 0.25 mol of KClin 1.00 kg of water
O a solution formed by dissolving 0.75 mol of KCl in 4.00 kg of water
O a solution formed by dissolving 0.25 mol of KCl in 0.50 kg of water
O all of the solutions described have the same freezing point.

Answer 1

The correct answer is option 1. The solution formed by dissolving 0.75 mol of KCl in 1.00 kg of water has the highest freezing point.

Step-by-step explanation:

The freezing point of a solution depends on the molality of the solution and the molal freezing point depression constant for the solvent. The greater the concentration of solute particles, the greater the freezing point depression and thus the lower the freezing point. In this case, we can calculate the molality of each solution and compare their freezing points:

Solution 1: Dissolving 0.75 mol of KCl in 1.00 kg of water

Molality = moles of solute / mass of solvent in kg = 0.75 mol / 1.00 kg = 0.75 m

Solution 2: Dissolving 0.25 mol of KCl in 1.00 kg of water

Molality = 0.25 mol / 1.00 kg = 0.25 m

Solution 3: Dissolving 0.75 mol of KCl in 4.00 kg of water

Molality = 0.75 mol / 4.00 kg = 0.1875 m

Solution 4: Dissolving 0.25 mol of KCl in 0.50 kg of water

Molality = 0.25 mol / 0.50 kg = 0.5 m

The solution with the highest molality is Solution 1 with a molality of 0.75 m. Therefore, Solution 1 (formed by dissolving 0.75 mol of KCl in 1.00 kg of water) has the highest freezing point depression and thus the lowest freezing point.