Question

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) 5.2 ppb Hg in H2O (b) 1.9 ppb CHCl3 in H2O (c) 36.0 ppm As in H2O (d) 0.22 ppm DDT (C14H9Cl5) in H2O

Answer 1

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) 5.2 ppb Hg in H2O (b) 1.9 ppb CHCl3 in H2O (c) 36.0 ppm As in H2O (d) 0.22 ppm DDT (C14H9Cl5) in H2O

1. Molar mass of Hg is 200.59

5.2 ppb in water means: 5.2 ×10^-3 ppm: 5.2 ×10^-3 mg in 1kg or 1liter of solution

200.59 gm in 1Lit = 1M

5.2 ×10^-6 gm in 1Lit = ?

Answer: 5.2 ×10^-6 gm in 1Lit = 2.592310^-6M

1. Molar mass of Chloroform is 119.38 g/mol

1.9 ppb CHCl3 in H2O means: 1.9×10^-3 ppm: 1.9×10^-3mg in 1Lit of solution

119.38 gm in 1Lit =1M

1. ×10^-6gm in 1Lit = ?

Answer: 1.9×10^-6gm in 1Lit = 1.591×10^-8M

1. Atomic weight of arsenic 74.9216 amu

36.0 ppm As in H2O means: 36 mg of As in 1Lit H2O: 36×10^-3 gm of As in 1Lit water

74.9216 gm in 1Lit = 1M

1. ×10^-3 gm of As in 1Lit = ?

Answer: 36×10^-3 gm of As in 1Lit = 4.8050×10^-4M

1. 0.22 ppm DDT (C14H9Cl5) in H2O

0.22 mg in 1Lit water: 0.22×10^-3 gm in 1Lit

354.49 g of DDT in 1Lit water = 1M

1. ×10^-3 gm in 1Lit = ?

Answer: 0.22×10^-3 gm in 1Lit = 6.2060×10^-7M