6. 47.14 points ZumChemP7 4.E.027 My Notes Ask Your Teacher The units of parts p

Question

6. 47.14 points ZumChemP7 4.E.027 My Notes Ask Your Teacher 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. solution kg solution In the case of very dilute aqueous solutions, a concentration of 1.0 ppm is equal to 1.0 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) 4.2 ppb Hg in H20 (b) 3.0 ppb CHCl3 in H20 (c) 37.0 ppm As in H20 (d) 0.30 ppm DDT (C14H9Cls) in H20 Need Help? .meer i Leer! Supporting Materials Periodic Table Constants and Factors Supplemental Data

Explanation / Answer

a)

4.2ppb = 0.0042ppm = 0.0042mg/L

0.0042mg = 0.0000042g

No of mole of Hg = mass of Hg/molar mass of Hg

= 0.0000042g/200.592g/mol = 2.09×10-8 mol

Therefore,

Molarity of Hg =2.09×10-8 M

b)

3.0ppb = 0.003ppm = 0.003mg/L

0.003mg = 0.000003g

No of mole of CHCl3 =0.000003g /119.37g/mol =2.51×10-8

Molarity of CHCl3 = 2.51×10-8M

c)

37ppm =37mg/L

37mg = 0.037g

No of mole of As = 0.037g/74.921g/mol = 4.94×10-4

Molarity of As = 4.94×10-4M

d)

0.30ppm = 0.30mg/L

0.30mg 0.00030g

no of mole of DDT = 0.00030g/354.48g/mole = 8.47×10-7

  Molarity of DDT = 8.46× 10-7M

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