Assuming that seawater is an aqueous solution of NaCl, what is its molarity? The density of seawater is 1.025 g/mL at 20 °C, and the NaCl concentration is 3.50 mass %.

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Calculate the mass of NaCl in 1 liter of seawater by using the given mass percentage: 3.50%. This means there are 3.50 grams of NaCl in every 100 grams of seawater.

Determine the mass of 1 liter of seawater using its density. Since the density is 1.025 g/mL, the mass of 1 liter (1000 mL) of seawater is 1.025 g/mL * 1000 mL.

Calculate the mass of NaCl in 1 liter of seawater using the mass percentage: (3.50/100) * mass of 1 liter of seawater.

Convert the mass of NaCl to moles using the molar mass of NaCl (approximately 58.44 g/mol).

Calculate the molarity of the NaCl solution by dividing the number of moles of NaCl by the volume of the solution in liters (1 liter in this case).

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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 seawater (1.025 g/mL) is essential for converting the mass of seawater into volume, which is necessary for calculating molarity. Understanding density helps in determining how much solution is present when given a mass.

Mass Percent Concentration

Mass percent concentration is a way to express the concentration of a solute in a solution, calculated as the mass of the solute divided by the total mass of the solution, multiplied by 100. In this case, a 3.50 mass % NaCl concentration means that there are 3.50 grams of NaCl in every 100 grams of seawater. This concept is vital for determining the amount of solute when calculating molarity.

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