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Ch.14 - Solutions
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoTro 6th EditionCh.14 - SolutionsProblema 58b
Capitolo 14, Problema 58b

An aqueous KNO3 solution is made using 55.3 g of KNO3 diluted to a total solution volume of 2.00 L. Calculate the molality of the solution. (Assume a density of 1.05 g>mL for the solution.)

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Calculate the molar mass of KNO_3 by adding the atomic masses of potassium (K), nitrogen (N), and oxygen (O).
Convert the mass of KNO_3 (55.3 g) to moles using the molar mass calculated in the previous step.
Determine the mass of the solution in grams by multiplying the volume of the solution (2.00 L) by the density (1.05 g/mL) and converting liters to milliliters.
Calculate the mass of the solvent (water) by subtracting the mass of KNO_3 from the total mass of the solution.
Calculate the molality of the solution by dividing the moles of KNO_3 by the mass of the solvent in kilograms.

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Molarity and Molality

Molarity (M) is defined as the number of moles of solute per liter of solution, while molality (m) is the number of moles of solute per kilogram of solvent. Understanding the difference between these two concentration units is crucial for solving problems involving solutions, especially when the volume and mass of the solvent are involved.
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Molality

Calculating Moles from Mass

To find the number of moles of a substance, you can use the formula: moles = mass (g) / molar mass (g/mol). For KNO3, the molar mass is approximately 101.1 g/mol. This calculation is essential for determining the concentration of the solution in terms of molality.
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03:12
Molar Mass Calculation Example

Density and Volume Relationships

Density is defined as mass per unit volume (g/mL or g/L). In this problem, the density of the solution is given as 1.05 g/mL, which allows us to convert the total volume of the solution into mass. This conversion is necessary to calculate the mass of the solvent, which is required for determining molality.
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01:09
Relationship of Volume and Moles Example
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