3. [Intro. analytical chemistry] - please solve and show work / explanations 3.

Question

3. [Intro. analytical chemistry] - please solve and show work / explanations

3. 18 points] The Department of Health and Human Services recently announced a change in the recommended amount of fluoride ion in drinking water, making the recommended maximum fluoride ion concentration about 0.70 mg/L. For any calculations below, assume a density of drinking water of 1.00 g/mL. a. What is this maximum fluoride concentration in units of ppb (by mass)? Express your answer with the correct number of significant figures. b. What is the maximum fluoride concentration in units of molarity? Express your answer with the correct number of significant figures.

Explanation / Answer

a) Concentration of Fluoride = 0.70 mg/L                      density of drinking water = 1.00 g/L

                                          = 0.70*10-3 g/L                  Mass of 1L water = 1.00* 103 g

Concentration of Fluoride in ppb = (mass of Fluoride/mass of solution)*109

   = (0.70*10-3 / 1.00* 103)*109 = 0.70*103 ppb

                           ( Upto 2 significant figures, as the division result should have 2 significant figures )

b) Atomic mass of F = 19 g

Moles of F = (0.70*10-3/19) = 3.7*10-2*10-3 =3.7*10-5 moles                 

( 0.70/19 = 0.0368421...........= 3.7*10-2 As the division result should have 2 significant figures)

Maximum concentration = 3.7*10-5 moles in 1L

Hence, Molarity = 3.7*10-5 M

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