13.87 The freezing point depression constants of the...

13.87 The freezing point depression constants of the solvents cyclohexane and naphthalene are $20.1^{\circ} \mathrm{C} / m$ and $6.94^{\circ} \mathrm{C} / \mathrm{m},$ respectively. Which solvent would give a more accurate result if you are using freezing point depression to determine the molar mass of a substance that is soluble in either one? Why?

Key Concepts

Freezing Point Depression

This phenomenon is a colligative property where the addition of a solute to a solvent lowers the freezing point of the solvent. It is used as a method to determine the molar mass of a solute by measuring the change in the freezing temperature of the solvent when the solute is dissolved.

Colligative Properties

Colligative properties depend on the number of solute particles present in a solution, not on their identity. They provide useful ways to determine molar mass and other physical properties because they produce measurable changes in characteristics such as boiling point, freezing point, vapor pressure, and osmotic pressure.

Freezing Point Depression Constant

The freezing point depression constant (Kf) is a property specific to each solvent that relates the magnitude of the freezing point change to the molality of the solution. A higher Kf value indicates that a given molality of solute will produce a larger depression, thereby improving the sensitivity and potential accuracy of molar mass determinations.

Measurement Sensitivity and Solvent Selection

When using freezing point depression to measure molar mass, selecting a solvent with a higher freezing point depression constant increases the sensitivity of the measurement. This is because a larger temperature change per unit of solute concentration minimizes relative measurement errors, making it easier to detect slight variations and thereby yielding more accurate results.

Transcript

Please give Ace some feedback