Ishwar S. answered • 06/25/18

Tutor

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University Professor - General and Organic Chemistry

Hello Sophie

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*