Fluoride ion is added to drinking water at low concentra- tions to prevent tooth decay. What mass of sodium fluoride (NaF) should be added to 750 L of water to make a solution that is 1.5 ppm in fluoride ion? (LO 13.5) (a) 1.1 g (b) 2.5 g (c) 0.51 g (d) 3.1 g

Parts per million (ppm) is a unit of measurement that expresses the concentration of a substance in a solution. It indicates how many parts of a solute are present in one million parts of the solution. For example, a concentration of 1.5 ppm means there are 1.5 grams of solute in one million grams of solution, which is crucial for calculating the required mass of sodium fluoride in this context.

Understanding molar mass is essential for converting between grams and moles of a substance. Sodium fluoride (NaF) has a molar mass of approximately 42 g/mol. Stoichiometry allows us to relate the mass of NaF needed to achieve the desired fluoride ion concentration in the water, enabling accurate calculations based on the ppm value.

Dilution is the process of reducing the concentration of a solute in a solution, typically by adding more solvent. In this case, knowing the volume of water (750 L) and the desired concentration (1.5 ppm) allows us to calculate the total mass of fluoride needed and subsequently determine how much sodium fluoride must be added to achieve that concentration in the water.