Calculate the molality of each of the following aqueous...

Calculate the molality of each of the following aqueous solutions: (a) $2.50 \mathrm{M} \mathrm{NaCl}$ solution (density of solution $=1.08 \mathrm{~g} / \mathrm{mL}$ ), (b) $48.2$ percent by mass $\mathrm{KBr}$ solution.

Key Concepts

Molality

Molality is a concentration unit defined as the number of moles of solute per kilogram of solvent. It is useful because it remains constant with temperature changes, as it depends only on mass, not volume.

Molarity

Molarity is a concentration term that represents the number of moles of solute present in one liter of solution. It is dependent on the volume of the solution and can change with temperature, unlike molality.

Density and Its Role in Conversions

Density provides the relationship between the mass and volume of a solution, which is crucial when converting between molarity (a volume-based measure) and molality (a mass-based measure). Knowing the density allows one to determine the total mass of the solution from its volume.

Percent by Mass (Mass Percent Composition)

Percent by mass indicates the mass of the solute divided by the total mass of the solution, multiplied by 100. This concept is essential for determining the amount of solute in a given mass of solution and for converting to other concentration units.

Conversion Techniques in Solution Calculations

Conversion techniques involve using the relationships among moles, mass, volume, density, and percent concentrations to shift between different units of concentration. These methods typically require determining the moles of solute, the mass of the solution, and then isolating the mass of the solvent to calculate molality.

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