You want to convert among molarity, molality, and mole...

Name: Problem 54, Chapter 13: Chemistry: The Molecular Nature of Matter and Change
Uploaded: 2020-06-24T21:30:38-08:00
Duration: 3 min 42 s
Channel: Keenan Mintz
Description: You want to convert among molarity, molality, and mole fraction of a solution. You know the masses of solute and solvent and the volume of solution. Is this enough information to carry out all the conversions? Explain.

You want to convert among molarity, molality, and mole fraction of a solution. You know the masses of solute and solvent and the volume of solution. Is this enough information to carry out all the conversions? Explain.

Key Concepts

Mole Fraction

Mole fraction is the ratio of the moles of one component to the total moles of all components in a solution. This unitless measure requires the calculation of moles from the given masses using the respective molar masses. Knowing the masses of both solute and solvent allows one to compute their mole fractions directly by summing the moles of each and forming the required ratio.

Data Sufficiency for Conversions

Having the masses of solute and solvent along with the volume of the solution provides sufficient information to perform conversions among molarity, molality, and mole fraction. This is because each of these concentration measures can be derived from the fundamental quantities of moles, mass, and volume, assuming that the molar masses are known. The volume directly gives you the pathway to compute molarity, and the masses permit the calculation of both molality and mole fraction.

Molarity

Molarity is defined as the number of moles of solute per liter of solution. It is a concentration unit that directly relates the amount of dissolved substance to the total volume of the mixture. When the volume is known and the moles of solute can be determined from its mass and molar mass, molarity can be calculated without needing additional density information.

Molality

Molality refers to the number of moles of solute per kilogram of solvent, making it a concentration measure that depends on the mass of the solvent rather than the volume of the solution. Since the mass of the solvent is provided, one can compute molality by converting the mass to kilograms and using the moles of solute, thus not requiring any additional volume-to-mass conversion factors.

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