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Ch.13 - Solutions & Their Properties
Chapter 13, Problem 70

What is the concentration of each of the following solutions?(b) The mole fraction of each component of a solution pre- pared by dissolving 2.25 g of nicotine, C10H14N2, in80.0 g of CH2Cl2

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Calculate the molar mass of nicotine (C10H14N2). Use the atomic masses: C = 12.01 g/mol, H = 1.008 g/mol, N = 14.01 g/mol. The formula for molar mass is: Molar mass = (number of C atoms x atomic mass of C) + (number of H atoms x atomic mass of H) + (number of N atoms x atomic mass of N).
Calculate the number of moles of nicotine using its mass and molar mass. The formula for number of moles is: Moles = mass / molar mass.
Calculate the molar mass of dichloromethane (CH2Cl2). Use the atomic masses: C = 12.01 g/mol, H = 1.008 g/mol, Cl = 35.45 g/mol. The formula for molar mass is: Molar mass = (number of C atoms x atomic mass of C) + (number of H atoms x atomic mass of H) + (number of Cl atoms x atomic mass of Cl).
Calculate the number of moles of dichloromethane using its mass and molar mass. The formula for number of moles is: Moles = mass / molar mass.
Calculate the mole fraction of each component. The mole fraction is given by the formula: Mole fraction of component = moles of component / total moles of all components.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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 solution. This dimensionless quantity helps in understanding the composition of solutions, especially in cases where the total mass or volume may not be easily measured.
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Calculating Moles from Mass

To find the mole fraction, it is essential to convert the mass of each component into moles. This is done using the formula: moles = mass (g) / molar mass (g/mol). The molar mass of a substance can be calculated by summing the atomic masses of all atoms in its molecular formula, allowing for accurate conversion from grams to moles.
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Molar Mass Calculation Example

Solution Composition

Understanding the composition of a solution involves recognizing the roles of solute and solvent. In this case, nicotine is the solute being dissolved in dichloromethane (CH2Cl2), the solvent. The total number of moles of both components is necessary to calculate the mole fraction, which reflects how much of each component is present relative to the total amount in the solution.
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