Chemistry question (1 Viewer)

[Nebuchanezzar]

This is beggining to annoy me greatly so I'm hoping some chemistry whiz will help me out.

k, I have 25ppm fluoride in a solution of 100ml (which originally came from a solution of 500ml). I need to find out how many grams this is of NaF. Simple? Here's the way I've been working it out:

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1ppm=1mg/L
25ppm=25mg/L
25mg=0.025g
=0.025g/L

For 100ml, divide 0.025 by 10 to obtain value of g/100ml
0.025g/L = 0.0025g/100mL

The solution originally contained 500ml, so times by 5 to get value of g/500mL
=0.0125g/500mL

I want to know how many moles of fluoride that is, so:
0.0125/19=0.000657moles fluoride

Since NaF is a 1:1 molecule, the moles of fluoride is equal to the amount of moles of NaF. So:
0.000657=mass/22.99+19 (mmF+mmNa)
0.000657x41.99 = mass
=0.027g NaF

But this seems way too small! Help? Anyone?

 

[undalay]

seems about right.

i got 0.028g (to 2 sig figs)
but i didnt round to the very end.

 

[doink]

it's in parts per million, so obviously it will be very small.