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Ch.13 - Solutions
Chapter 13, Problem 6

You can purchase hydrochloric acid in a concentrated form that is 37.0% HCl by mass and that has a density of 1.20 g>mL. Describe exactly how to prepare 2.85 L of 0.500 M HCl from the concentrated solution.

Verified step by step guidance
1
Calculate the moles of HCl needed using the formula: \( \text{Moles of HCl} = \text{Volume (L)} \times \text{Molarity (M)} \).
Determine the mass of HCl in the concentrated solution using the percentage by mass: \( \text{Mass of HCl} = \text{Mass of solution} \times 0.37 \).
Calculate the volume of the concentrated solution needed using its density: \( \text{Volume} = \frac{\text{Mass}}{\text{Density}} \).
Use the dilution equation \( M_1V_1 = M_2V_2 \) to find the volume of concentrated HCl needed, where \( M_1 \) and \( V_1 \) are the molarity and volume of the concentrated solution, and \( M_2 \) and \( V_2 \) are the molarity and volume of the diluted solution.
Measure the calculated volume of concentrated HCl and dilute it with water to a total volume of 2.85 L.

Key Concepts

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

Molarity (M)

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in moles per liter (mol/L). To prepare a solution of a specific molarity, one must calculate the amount of solute needed based on the desired volume and molarity, which is crucial for diluting concentrated solutions.
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Dilution

Dilution is the process of reducing the concentration of a solute in a solution, typically by adding more solvent. The dilution equation, M1V1 = M2V2, relates the initial and final molarities (M1 and M2) and volumes (V1 and V2) of the solution. Understanding this concept is essential for accurately preparing solutions from concentrated stock.
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Density and Mass Percent

Density is the mass of a substance per unit volume, often expressed in grams per milliliter (g/mL). Mass percent indicates the mass of solute in a given mass of solution. For hydrochloric acid, knowing its density and mass percent allows one to calculate the mass of HCl in a specific volume of concentrated solution, which is necessary for preparing the desired diluted solution.
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