Textbook Question
Describe how to prepare each solution from the dry solute and the solvent. c. 125 g of 1.0% NaNO3 solution by mass
Ch.14 - Solutions
Chapter 14, Problem 64b
A solution is prepared by dissolving 20.2 mL of methanol (CH3OH) in 100.0 mL of water at 25 °C. The final volume of the solution is 118 mL. The densities of methanol and water at this temperature are 0.782 g/mL and 1.00 g/mL, respectively. For this solution, calculate the concentration in each unit. b. molality
Verified step by step guidance1
Calculate the mass of methanol using its volume and density. Use the formula: mass = volume × density.
Calculate the mass of water using its volume and density. Use the formula: mass = volume × density.
Convert the mass of methanol to moles using its molar mass. Methanol (CH3OH) has a molar mass of approximately 32.04 g/mol. Use the formula: moles = mass / molar mass.
Calculate the mass of the solvent (water) in kilograms, as molality is expressed in moles of solute per kilogram of solvent.
Calculate the molality of the solution using the formula: molality = moles of solute / kilograms of solvent.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Concentration Units
Concentration can be expressed in various units, including molarity (moles of solute per liter of solution) and molality (moles of solute per kilogram of solvent). Understanding these units is crucial for accurately calculating the concentration of a solution, as they reflect different aspects of solute and solvent relationships.
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SI Units
Molarity vs. Molality
Molarity is defined as the number of moles of solute divided by the volume of the solution in liters, while molality is defined as the number of moles of solute divided by the mass of the solvent in kilograms. The distinction is important because molarity can change with temperature due to volume expansion, whereas molality remains constant as it depends solely on mass.
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Density and Volume Calculations
Density is the mass per unit volume of a substance, and it is essential for converting between mass and volume. In this problem, the densities of methanol and water allow for the calculation of the mass of each component, which is necessary for determining molality, as it requires the mass of the solvent.
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Related Practice
Textbook Question
A solution is prepared by dissolving 20.2 mL of methanol (CH3OH) in 100.0 mL of water at 25 °C. The final volume of the solution is 118 mL. The densities of methanol and water at this temperature are 0.782 g/mL and 1.00 g/mL, respectively. For this solution, calculate the concentration in each unit. a. molarity
Textbook Question
A solution is prepared by dissolving 20.2 mL of methanol (CH3OH) in 100.0 mL of water at 25 °C. The final volume of the solution is 118 mL. The densities of methanol and water at this temperature are 0.782 g/mL and 1.00 g/mL, respectively. For this solution, calculate the concentration in each unit. c. percent by mass
Textbook Question
A solution is prepared by dissolving 20.2 mL of methanol (CH3OH) in 100.0 mL of water at 25 °C. The final volume of the solution is 118 mL. The densities of methanol and water at this temperature are 0.782 g/mL and 1.00 g/mL, respectively. For this solution, calculate the concentration in each unit. d. mole fraction
Textbook Question
A solution is prepared by dissolving 20.2 mL of methanol (CH3OH) in 100.0 mL of water at 25 °C. The final volume of the solution is 118 mL. The densities of methanol and water at this temperature are 0.782 g/mL and 1.00 g/mL, respectively. For this solution, calculate the concentration in each unit. e. mole percent