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. Assuming that the volumes of the solute and solvent are additive, what is the molarity of thiophene in the solution?

Name: Chemistry: The Central Science
Author: Brown
ISBN: 9780134414232

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Calculate the volume of thiophene using its mass and density. Use the formula: \( \text{Volume} = \frac{\text{Mass}}{\text{Density}} \).

Determine the total volume of the solution by adding the volume of thiophene to the volume of toluene.

Calculate the number of moles of thiophene using its mass and molar mass. Use the formula: \( \text{Moles} = \frac{\text{Mass}}{\text{Molar Mass}} \).

Use the total volume of the solution (in liters) and the moles of thiophene to calculate the molarity. Use the formula: \( \text{Molarity} = \frac{\text{Moles of Solute}}{\text{Volume of Solution in Liters}} \).

Ensure all units are consistent, particularly converting mL to L for the volume of the solution.

주요 개념

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Density and Volume Relationships

Density is defined as mass per unit volume (g/mL). Understanding how to convert between mass and volume using density is crucial for solving problems involving solutions. In this case, the densities of toluene and thiophene allow us to determine the volume of thiophene when given its mass, which is essential for calculating molarity.

Molarity

Molarity (M) is a measure of concentration defined as the number of moles of solute per liter of solution. To calculate molarity, one must first convert the mass of the solute (thiophene) into moles using its molar mass. The final step involves dividing the number of moles by the total volume of the solution in liters, which is critical for determining the concentration of thiophene in the solution.

Additivity of Volumes

The assumption that the volumes of solute and solvent are additive simplifies the calculation of the total volume of the solution. This means that when thiophene is dissolved in toluene, the total volume can be approximated by simply adding the volume of toluene to the volume of thiophene. This concept is important for accurately determining the final volume used in the molarity calculation.