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chemistry

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Calculating Parts per million

Helium gas, 3.0 x 10^-4 is dissolved in 200.0 g of water. Express this concentrartion in parts per million.

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    He = 3.0 x 10^-4 what? grams?
    [3.0 x 10^-4 g/200.0 g water]*100 = %He. right?
    Technically, the denominator is (200+0.0003) but we'll ignore the small number. So now you have percent, which is parts per hundred, just multiply by what factor to convert to parts per million.
    ??pph x (10^6/10^2) = ?? ppm.
    I just remember that 1 ppm is 1 mg/L.
    3.0 x 10^-4 g = 0.3 mg. Put that in 200 mL = 0.3 mg/200 mL = 0.00150 mg/mL and multiply by 1000 to convert to L so that is 1.50 ppm. Is that the same number as the first method?

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