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.)

Verified step by step guidance

1. Identify the given information: the mass percent of NaOCl is 4.55%, and the density of the solution is 1.02 g/mL.
2. Assume a certain volume of the solution to simplify calculations, such as 1 liter (1000 mL).
3. Calculate the mass of the solution using the density: \( \text{mass} = \text{density} \times \text{volume} \).
4. Determine the mass of NaOCl in the solution using the mass percent: \( \text{mass of NaOCl} = \frac{4.55}{100} \times \text{mass of solution} \).
5. Convert the mass of NaOCl to moles using its molar mass: \( \text{moles of NaOCl} = \frac{\text{mass of NaOCl}}{\text{molar mass of NaOCl}} \).

Key Concepts

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.