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Ch.14 - Solutions
Tro - Chemistry: A Molecular Approach 5th Edition
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Tutti i libri di testoTro 5th EditionCh.14 - SolutionsProblema 77
Capitolo 14, Problema 77

A glucose solution contains 55.8 g of glucose (C6H12O6) in 455 g of water. Determine the freezing point and boiling point of the solution.

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Identify the colligative properties involved: freezing point depression and boiling point elevation.
Calculate the molality (m) of the solution using the formula: \( m = \frac{\text{moles of solute}}{\text{kilograms of solvent}} \). First, find the moles of glucose by dividing the mass of glucose by its molar mass.
Use the freezing point depression formula: \( \Delta T_f = i \cdot K_f \cdot m \), where \( i \) is the van't Hoff factor (1 for glucose), \( K_f \) is the cryoscopic constant for water, and \( m \) is the molality.
Use the boiling point elevation formula: \( \Delta T_b = i \cdot K_b \cdot m \), where \( K_b \) is the ebullioscopic constant for water.
Determine the new freezing and boiling points by subtracting \( \Delta T_f \) from the normal freezing point of water (0°C) and adding \( \Delta T_b \) to the normal boiling point of water (100°C).

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Colligative Properties

Colligative properties are physical properties of solutions that depend on the number of solute particles in a given amount of solvent, rather than the identity of the solute. These properties include boiling point elevation and freezing point depression, which occur when a solute is added to a solvent, affecting the solvent's phase changes.
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01:26
Colligative Properties

Freezing Point Depression

Freezing point depression is a colligative property that describes the decrease in the freezing point of a solvent when a solute is dissolved in it. The extent of freezing point depression can be calculated using the formula ΔTf = i * Kf * m, where ΔTf is the change in freezing point, i is the van 't Hoff factor, Kf is the freezing point depression constant, and m is the molality of the solution.
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01:59
Freezing Point Depression

Boiling Point Elevation

Boiling point elevation is another colligative property that refers to the increase in the boiling point of a solvent when a solute is added. This phenomenon can be quantified using the formula ΔTb = i * Kb * m, where ΔTb is the change in boiling point, i is the van 't Hoff factor, Kb is the boiling point elevation constant, and m is the molality of the solution.
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Boiling Point Elevation
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Domanda del libro di testo

A solution contains a mixture of pentane and hexane at room temperature. The solution has a vapor pressure of 258 torr. Pure pentane and hexane have vapor pressures of 425 torr and 151 torr, respectively, at room temperature. What is the mole fraction composition of the mixture? (Assume ideal behavior.)

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