The sterile saline solution used to rinse contact lenses can be made by dissolving 400 mg of NaCl in sterile water and diluting to 100 mL. What is the molarity of the solution?

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). To calculate molarity, one must know the amount of solute in grams, convert it to moles using the molar mass, and then divide by the volume of the solution in liters.

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). For sodium chloride (NaCl), the molar mass is approximately 58.44 g/mol, calculated by adding the atomic masses of sodium (Na) and chlorine (Cl). This value is essential for converting grams of solute into moles when calculating molarity.

Dilution is the process of reducing the concentration of a solute in a solution, usually by adding more solvent. In this context, the saline solution is prepared by dissolving a specific mass of NaCl in a known volume of sterile water, which allows for precise control over the final concentration. Understanding dilution is crucial for accurately determining the molarity of the solution.