1 part per million is the same as
1 mcg/mL (mcg = 1 micro gram = 1 10^-6 grams).
125 ppm = 125 mcg/mL
125 mcg/ml [1 gram / 1 10^6 mgrm] = 1.25 10^-4 grams
The density of hard water is 1.000 grams / mL
50 mL of water contains 1.25 10^-4 grams.
given mass = 1.25 10^-4
Molar mass = 100.0 grams / mole
n = ?????
n = 1.25 10^-4/100 = 1.25 10^-6 moles.
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