Question

The pesticide DDT (C14H9Cl5)... Express these concentrations in ppm and in milimoles per liter.

Orchard - Sample size: 250.0mL Mass of DDT: 0.030 mg

Residential - Sample size: 1.750 L Mass of DDT: 0.035 mg

Residential After a Storm - Sample size: 50.0 mL Mass of DDT: 0.57 mg

Answers are: Orchard: 1.2 x 10^-7 ppm, 3.4 x 10^-4 mmol/L; Residential: 2.0 x 10^-8, 5.6 x 10^-5 mmol/L; After-storm: 1.1 x 10^-5 ppm, 3.2 x 10^-2 mmol/L

I used the ppm formula but I'm not getting the answers the textbook is stating

Answer 1

molemass C14H9Cl5: 12*14+9+35*5 =352

Orchard: 4*.030E-3/352E3== 3.40909091e-10

After storm: (.57E-3)/352E3 * 1/50E-6
= 3.23863636e-6 millimole/liter

Answer 2

Thank You. Where do you get the 4 from the orchard calculation? And how I would figure out the ppm?

Answer 3

the four is from the volume, you had only 1/4 liter...so four times as much ddt per liter.

ppm? I have no clue, because you cant convert the volume to particles of something else. If you knew what the other ingredents were, you could do it.