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Ch.14 - Solutions
All textbooksTro 6th EditionCh.14 - SolutionsProblem 68b
Chapter 14, Problem 68b

Describe how to prepare each solution from the dry solute and the solvent. b. 125 g of 0.100 m NaNO3

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Determine that you need to prepare a solution with a specific molality (0.100 m) using sodium nitrate (NaNO₃) as the solute and water as the solvent. Molality is defined as moles of solute per kilogram of solvent.
Use the formula for molality: \( m = \frac{\text{moles of solute}}{\text{kilograms of solvent}} \). Rearrange to find moles of solute: \( \text{moles of solute} = m \times \text{kilograms of solvent} \).
Since the problem specifies 125 g of solution, you need to find the mass of the solvent (water). Assume the mass of the solute is negligible compared to the solvent for this calculation, or adjust based on the solute's mass if needed.
Use the molar mass of NaNO₃ to convert moles of solute to grams. The molar mass of NaNO₃ is approximately 85 g/mol. Use the formula: \( \text{mass of NaNO₃} = \text{moles of NaNO₃} \times \text{molar mass of NaNO₃} \).
Weigh the calculated mass of NaNO₃ and dissolve it in the calculated mass of water to achieve the desired molality. Ensure thorough mixing to achieve a homogeneous solution.

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Key Concepts

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

Molarity

Molarity (M) is a measure of concentration defined as the number of moles of solute per liter of solution. It is crucial for preparing solutions, as it allows chemists to quantify how much solute is needed to achieve a desired concentration. In this case, a 0.100 M solution of NaNO3 means there are 0.100 moles of NaNO3 in every liter of the final solution.
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Calculating Moles

To prepare a solution, it is essential to calculate the number of moles of solute required. The number of moles can be determined using the formula: moles = mass (g) / molar mass (g/mol). For NaNO3, the molar mass is approximately 85 g/mol, so to find out how many moles are in 125 g, one would divide 125 g by 85 g/mol.
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Dilution and Solution Preparation

Preparing a solution involves dissolving the calculated amount of solute in a specific volume of solvent. For a 0.100 M NaNO3 solution, after determining the required moles from the mass, the solute should be added to a volumetric flask with a portion of solvent, mixed until dissolved, and then diluted to the final volume with additional solvent to ensure the correct concentration.
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Related Practice
Textbook Question

Lead is a toxic metal that affects the central nervous system. A Pb-contaminated water sample contains 0.0011% Pb by mass. How much of the water (in mL) contains 150 mg of Pb? (Assume a density of 1.0 g/mL.)

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

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