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Ch.13 - Properties of Solutions
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoBrown 14th EditionCh.13 - Properties of SolutionsProblema 50a
Capitolo 13, Problema 50a

The density of toluene (C7H8) is 0.867 g/mL, and the density of thiophene (C4H4S) is 1.065 g/mL. A solution is made by dissolving 8.10 g of thiophene in 250.0 mL of toluene. (a) Calculate the mole fraction of thiophene in the solution.

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Step 1: Calculate the number of moles of each component. The number of moles is given by the formula: n = mass / molar mass. The molar mass of thiophene (C4H4S) is approximately 84.14 g/mol and the molar mass of toluene (C7H8) is approximately 92.14 g/mol.
Step 2: Use the given mass of thiophene (8.10 g) and the molar mass from step 1 to calculate the number of moles of thiophene.
Step 3: Use the given volume of toluene (250.0 mL), the density of toluene (0.867 g/mL), and the molar mass from step 1 to calculate the number of moles of toluene.
Step 4: The mole fraction of a component in a solution is given by the formula: X = n_component / n_total. Calculate the total number of moles (n_total) by adding the number of moles of thiophene and toluene.
Step 5: Substitute the number of moles of thiophene and the total number of moles into the formula from step 4 to calculate the mole fraction of thiophene in the solution.

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Mole Fraction

Mole fraction is a way of expressing the concentration of a component in a mixture. It is defined as the ratio of the number of moles of a specific component to the total number of moles of all components in the mixture. This concept is crucial for understanding the composition of solutions and is often used in calculations involving colligative properties.
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Mole Fraction Formula

Density and Volume Relationship

Density is defined as mass per unit volume and is a key property of substances. In this context, knowing the density of toluene allows us to convert the volume of toluene (250.0 mL) into mass, which is necessary for calculating the total number of moles in the solution. Understanding this relationship is essential for solving problems involving solutions and mixtures.
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Relationship of Volume and Moles Example

Molar Mass Calculation

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). To calculate the mole fraction of thiophene, we need to determine the number of moles of thiophene and toluene. This requires knowing the molar masses of both compounds, which can be calculated from their chemical formulas by summing the atomic masses of their constituent elements.
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Molar Mass Calculation Example
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