Ch.14 - Solutions

Tro - Chemistry: A Molecular Approach 6th Edition

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Tro 6th Edition

Ch.14 - Solutions

Problem 72

Chapter 14, Problem 72

One brand of laundry bleach is an aqueous solution containing 4.55% sodium hypochlorite (NaOCl) by mass. What is the molarity of this solution? (Assume a density of 1.02 g/mL.)

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Identify the given information: the mass percent of NaOCl is 4.55%, and the density of the solution is 1.02 g/mL.

Assume a certain volume of the solution to simplify calculations, such as 1 liter (1000 mL).

Calculate the mass of the solution using the density: \( \text{mass} = \text{density} \times \text{volume} \).

Determine the mass of NaOCl in the solution using the mass percent: \( \text{mass of NaOCl} = \frac{4.55}{100} \times \text{mass of solution} \).

Convert the mass of NaOCl to moles using its molar mass: \( \text{moles of NaOCl} = \frac{\text{mass of NaOCl}}{\text{molar mass of NaOCl}} \).

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Key Concepts

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

Molarity

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) and is crucial for understanding how much solute is present in a given volume of solution. To calculate molarity, one must know the mass of the solute, its molar mass, and the total volume of the solution.

Density

Density is the mass of a substance per unit volume, typically expressed in grams per milliliter (g/mL) or kilograms per cubic meter (kg/m³). In this context, the density of the bleach solution allows us to convert the mass of the solution into volume, which is necessary for calculating molarity. Knowing the density helps in determining how much solution corresponds to a given mass.

Percent by Mass

Percent by mass is a way to express the concentration of a component in a mixture, calculated as the mass of the solute divided by the total mass of the solution, multiplied by 100. In this question, the 4.55% sodium hypochlorite indicates that there are 4.55 grams of NaOCl in every 100 grams of the solution. This information is essential for determining the amount of solute present for molarity calculations.

Related Practice

Textbook Question

A solution contains 50.0 g of heptane (C₇H₁₆) and 50.0 g of octane (C₈H₁₈) at 25 °C. The vapor pressures of pure heptane and pure octane at 25 °C are 45.8 torr and 10.9 torr, respectively. Assuming ideal behavior, answer the following: d. Why is the composition of the vapor different from the composition of the solution?

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Textbook Question

Household hydrogen peroxide is an aqueous solution containing 3.0% hydrogen peroxide by mass. What is the molarity of this solution? (Assume a density of 1.01 g/mL.)

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. e. mole percent

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Textbook Question

An aqueous solution contains 25% HCl by mass. Calculate the molality and mole fraction of the solution.

Textbook Question

Calculate the vapor pressure of a solution containing 38.3 g of glycerin (C3H8O3) in 135 mL of water at 30.0 °C. The vapor pressure of pure water at this temperature is 31.8 torr. Assume that glycerin is not volatile and dissolves molecularly (i.e., it is not ionic), and use a density of 1.00 g>mL for the water.

Textbook Question

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