Question

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

Short answer

The molarity of the bleach solution is approximately 0.623 M.

Step-by-step solution

Calculate the mass of sodium hypochlorite per liter of solution

To calculate the mass of sodium hypochlorite in a 1 liter (1000 mL) solution, use the density of the solution to find the total mass, and then apply the percentage by mass to find the mass of sodium hypochlorite. Density is mass per unit volume, so multiplying the density by the volume will give the mass: Mass of solution = density x volume = 1.02 g/mL x 1000 mL = 1020 g. Then find the mass of sodium hypochlorite: Mass of NaOCl = 0.0455 x mass of solution = 0.0455 x 1020 g = 46.41 g.

Convert mass of NaOCl to moles

Using the molar mass of NaOCl (22.99 g/mol for Na, 15.999 g/mol for O, and 35.45 g/mol for Cl, adding up to 74.44 g/mol), convert the mass of NaOCl to moles. Number of moles = mass (g) / molar mass (g/mol) = 46.41 g / 74.44 g/mol = 0.623 moles.

Calculate the molarity of the solution

Molarity is the number of moles of solute per liter of solution. Since we have the moles of NaOCl and we know that our solution is 1 liter, the molarity is simply the number of moles: Molarity = moles of solute / liters of solution = 0.623 moles / 1 L = 0.623 M.

Key concepts

Sodium Hypochlorite

Sodium hypochlorite (NaOCl) plays a crucial role in everyday life, most notably as an active ingredient in bleaching and disinfecting products. This chemical compound is a sodium salt of hypochlorous acid and is highly effective in killing bacteria, fungi, and viruses, making it a staple in household cleaning.

Understanding the chemical properties, safety measures, and handling of sodium hypochlorite is important for its proper use. When dissolved in water, sodium hypochlorite produces an aqueous solution that can oxidize a wide range of organic compounds, which is why it's so effective as a bleaching agent.

In context to the exercise, knowing the percentage of sodium hypochlorite in a solution helps in determining the molarity, which is vital to assess the solution's strength for various applications. The concentration indicates how much sodium hypochlorite is present in comparison to the whole solution, an essential aspect to consider for successful application in cleaning or disinfection.

Molecular Mass

Molecular mass, which is the sum of the mass of all atoms in a molecule, plays a pivotal role in chemistry, particularly in the quantification of chemical substances. The molecular mass of sodium hypochlorite (NaOCl) is calculated by adding the atomic masses of sodium (Na), oxygen (O), and chlorine (Cl).

The molecular mass is not only crucial to determine the molar mass but also is essential in converting between moles and grams, a fundamental process in stoichiometric calculations. Utilizing the periodic table, one can find the atomic masses of each element: Na (22.99 g/mol), O (15.999 g/mol), and Cl (35.45 g/mol), which amounts to a total molecular mass of 74.44 g/mol for NaOCl. In practical scenarios, understanding molecular mass enables the calculation of moles from a given mass, which is necessary to derive the molarity in the exercise at hand.

Solution Concentration

Solution concentration is a measure of the amount of solute that is dissolved in a solvent. In chemistry, molarity is one of the commonly used units for concentration, expressing moles of solute per liter of solution. Molarity has profound implications in chemical reactions, dilutions, and even in regulating the precise strength of a mixture.

As it pertains to the textbook exercise, the molarity can be calculated after determining the mass of sodium hypochlorite in one liter of solution and then converting that mass to moles using the compound's molar mass. The molarity, denoted as M, illustrates the solution's concentration in terms of its chemical reactivity and effectiveness as a cleaning agent.

The accuracy of this calculation depends on precise measurements and a clear understanding of the relationships between mass, moles, and molarity. When students grasp these concepts, they are able to move forward with confidence in both theoretical and practical chemical applications.