The normal boiling point of ethanol, CH3 CH2 OH, is 78.4^∘ C . When 9.15 g of a soluble nonelect

step 1 Okay, so for this question we are given the normal boiling point of ethanol We're given the mass

The normal boiling point of ethanol, CH3 CH2 OH, is 78.4^∘ C...

The normal boiling point of ethanol, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH},$ is $78.4^{\circ} \mathrm{C} .$ When 9.15 $\mathrm{g}$ of a soluble nonelectrolyte is dissolved in 100.0 $\mathrm{g}$ of ethanol at that temperature, the vapor pressure of the solution is $7.40 \times 10^{2}$ torr. What is the molar mass of the solute?

Key Concepts

Colligative Properties

Colligative properties are characteristics of solutions that depend on the number of solute particles present, not on their chemical identity. This includes alterations in boiling point, freezing point, vapor pressure, and osmotic pressure when a solute is dissolved in a solvent. These properties enable the determination of solute quantities and their molar masses based on the observed changes in the physical properties of the solvent.

Raoult's Law

Raoult's Law relates the vapor pressure of a solvent in an ideal solution to the mole fraction of the solvent. According to this law, the vapor pressure of the solution is equal to the product of the mole fraction of the solvent and the vapor pressure of the pure solvent. This principle is essential for understanding how the addition of a nonvolatile solute lowers the vapor pressure of the solution.

Mole Fraction

Mole fraction is a way to express the concentration of a component in a mixture by dividing the number of moles of that component by the total number of moles of all components present. In the context of vapor pressure lowering, it is used to determine the proportion of solvent in the solution, which in turn affects the vapor pressure according to Raoult's Law.

Molar Mass Determination Using Colligative Properties

Molar mass determination utilizing colligative properties involves using measurable changes in a solvent's physical properties, such as vapor pressure lowering, to calculate the number of moles of solute added. By combining this mole count with the known mass of the solute, its molar mass can be computed. This method is particularly valuable when dealing with nonvolatile solutes in solutions and relies on the principles of colligative properties.

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