Ch.4 - Reactions in Aqueous Solution

Brown - Chemistry: The Central Science 14th Edition

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Brown 14th Edition

Ch.4 - Reactions in Aqueous Solution

Problem 77

Chapter 4, Problem 77

Pure acetic acid, known as glacial acetic acid, is a liquid with a density of 1.049 g/mL at 25 C. Calculate the molarity of a solution of acetic acid made by dissolving 20.00 mL of glacial acetic acid at 25 C in enough water to make 250.0 mL of solution.

Verified step by step guidance

Determine the mass of glacial acetic acid using its volume and density: \( \text{mass} = \text{density} \times \text{volume} \).

Calculate the number of moles of acetic acid using its molar mass: \( \text{moles} = \frac{\text{mass}}{\text{molar mass}} \). The molar mass of acetic acid (CH₃COOH) is approximately 60.05 g/mol.

Determine the volume of the solution in liters. Since the final volume of the solution is 250.0 mL, convert this to liters: \( 250.0 \text{ mL} = 0.2500 \text{ L} \).

Calculate the molarity of the acetic acid solution using the formula: \( \text{Molarity} = \frac{\text{moles of solute}}{\text{liters of solution}} \).

Combine the calculated moles of acetic acid and the volume of the solution in liters to find the molarity.

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Key Concepts

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

Density

Density is defined as mass per unit volume and is a crucial property of substances. In this context, the density of glacial acetic acid (1.049 g/mL) allows us to convert the volume of acetic acid used (20.00 mL) into mass, which is essential for calculating molarity.

Molarity

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. To find the molarity of the acetic acid solution, we need to determine the number of moles of acetic acid from its mass and then divide by the total volume of the solution in liters.

Moles and Molar Mass

Moles are a unit of measurement in chemistry that quantify the amount of substance. The molar mass of acetic acid (approximately 60.05 g/mol) is used to convert the mass of acetic acid obtained from the density calculation into moles, which is necessary for the molarity calculation.

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