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The units of parts per million (ppm) and parts per billion (ppb) are commonly used by environmental chemists. In general, 1 ppm means 1 part of solute for every 106 parts of solution. (Both solute and solution are measured using the same units.) Mathematically, by mass, ppm can be expressed as shown below.

ppm = µg solute/ g solution = mg solute/ kg solution

In the case of very dilute aqueous solutions, a concentration of 1.0 ppm is equal to 1.0 µg of solute per 1.0 mL of solution, which equals 1.0 g of solution. Parts per billion is defined in a similar fashion. Calculate the molarity of each of the following aqueous solutions.

(a) 4.9 ppb Hg in H2O

__M

(b) 1.8 ppb CHCl3 in H2O

__M

(c) 33.0 ppm As in H2O

__M

(d) 0.28 ppm DDT (C14H9Cl5) in H2O

__M

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1 answer
  1. I have another unit I use. 1 ppm = 1 mg solute/1 L solution and
    1 ppb = 1 ug solute/1 L solution.
    a, So 4.9 ppb Hg = 4.9 ug Hg/L
    Convert ug Hg to grams Hg.
    Convert g Hg to mols Hg and since mols/L is the definition of M that is it.

    The others are done the same way. Post your work if you get stuck.

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