An aqueous solution contains 5.0% NaCl by mass. How do you calculate the molality and mole fraction of the solution?

Verified step by step guidance

Step 1: Define molality. Molality (m) is defined as the number of moles of solute (NaCl) per kilogram of solvent (water).

Step 2: Calculate the mass of NaCl in the solution. Assume you have 100 g of solution, which contains 5.0 g of NaCl.

Step 3: Calculate the mass of the solvent (water). Subtract the mass of NaCl from the total mass of the solution: 100 g - 5.0 g = 95.0 g of water.

Step 4: Convert the mass of water to kilograms. Since 1 kg = 1000 g, convert 95.0 g to kg by dividing by 1000.

Step 5: Calculate the moles of NaCl. Use the molar mass of NaCl (approximately 58.44 g/mol) to convert the mass of NaCl to moles by dividing 5.0 g by the molar mass.

Key Concepts

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

Molality

Molality is a measure of the concentration of a solute in a solution, defined as the number of moles of solute per kilogram of solvent. It is expressed in moles per kilogram (mol/kg) and is particularly useful in situations where temperature changes may affect volume, as it relies on mass rather than volume.

Mole Fraction

Mole fraction is a way to express the concentration of a component in a mixture, calculated as the ratio of the number of moles of that component to the total number of moles of all components in the mixture. It is a dimensionless quantity and is useful for understanding the composition of solutions, especially in thermodynamic calculations.

Mass Percent

Mass percent is a way to express the concentration of a solute in a solution, calculated as the mass of the solute divided by the total mass of the solution, multiplied by 100. In this case, a 5.0% NaCl solution means that there are 5 grams of NaCl in every 100 grams of solution, which is essential for determining the amounts needed for calculating molality and mole fraction.

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