Chemistry Word Problem #2. Please help asap!

Question

The optimal level of fluoride in drinking water suggested by the World Health Organization in 1994 is between 0.5mg/L and 1.0mg/L. How many moles of sodium fluoride would have to be added to pure distilled water to have a water sample within this optimal range?

Thank you in advance, another word problem I am having trouble comprehending. Please help as soon as possible!

Answer 1

So this is a conversion problem between mass and moles. Since we want the fluoride levels between 0.5mg/L and 1.0 mg/L, let's see how many moles there are in 0.75 mg/L since that is the mid point of the range.

We will also need the Molar Mass of Sodium Fluoride = 42 g/mol = 23(Na)+ 19(F)

So 0.75 mg * 1 g / 1000mg = 0.00075 g of NaF

Then we can convert this to moles

0.00075 g * 1 mol NaF / 42 g = 1.8*10^-5 moles of NaF (2 sig figs)

So we would need to add 1.8*10^-5 moles of Sodium Fluoride for every Liter of distilled water.