This question involves converting the concentration of a solution from one unit (%-w/v) to another (Molarity).
First, we need to determine how many grams of NaF are in 0.5 oz of the mouthwash with a concentration of 0.05%-(w/v).
1 oz = 29.6 mL, therefore, 0.5 oz = 14.8 mL
By definition, the 0.05%-(w/v) NaF solution contains 0.05 g NaF / 100 mL solution.
g of NaF in 0.5 oz of 0.05%-(w/v) solution = (0.05 g NaF / 100 mL solution) x 14.8 mL = 0.0074 g NaF
To calculate Molarity, we first need to convert mass of NaF from above to moles of NaF using its molar mass (42 g/mol).
0.0074 g NaF x 1 mol NaF / 42 g NaF = 0.00018 mol NaF
Finally, Molarity is moles of solute divided by the volume in units of Liters (M = mol / L)
Volume in Liters = 14.8 mL x 1 L / 1000 mL = 0.0148 L
Molarity (M) = 0.00018 mol / 0.0148 L = 0.012 M