Modeling Tools for Environmental Engineers and Scientists

(2) In the water phase, the mass ratio of 1 ppm can be converted to mole ormass concentration form using the density of water, which is 1 g/cc at4ºC and 1 atm:1 ppm =1 g of chemical1 ppm ≡ 1 g cm3 100 3 cm 3 g3m ≡ 1 m3 ≡ 1 m g1,000,000 g of waterLg≡ 1 m3 m ol90 e g≡ 0.011 m olesm 3(3) In the soil phase, the conversion is direct:1 ppm =1 g of chemical1 ppm = 10 00gkg 1000 mgg = 1 m g1,000,000 g of soilkgWorked Example 4.2Analysis of a water sample from a lake gave the following results: volumeof sample = 2 L, concentration of suspended solids in the sample = 15 mg/L,concentration of a dissolved chemical = 0.01 moles/L, and concentration ofthe chemical adsorbed onto the suspended solids = 500 µg/g solids. If themolecular weight of the chemical is 125, determine the total mass of thechemical in the sample.Solution1 g of chemical1,000,000 g of water1 g of chemical1,000,000 g of soilTotal mass of chemical can be found by summing the dissolved mass andthe adsorbed mass. Dissolved mass can be found from the given molar concentration,molecular weight, and sample volume. The adsorbed mass can befound from the amount of solids in the sample and the adsorbed concentration.The amount of solids can be found from the concentration of solids inthe sample.Dissolved concentration = molar concentration * MW= 0.001 mo les 125g gL g mole= 0.125 L© 2002 by CRC Press LLC