Part B: Parts Per Units Parts per million (ppm) and parts per billion (ppb) are
ID: 551968 • Letter: P
Question
Part B: Parts Per Units Parts per million (ppm) and parts per billion (ppb) are common units for environmen- tal samples. The calculations are very similar to the percentage units, (which are es- sentially parts per hundred units). The mass units must be the same for the numerator and denominator, so these units cancel during the calculations. Please answer the following questions involving the parts per of your calculations. units, show all 7. A sample of river water was analyzed, and it was determined that there was 0.000012 g of lead in 1000.0 g of river water. What is the concentration of lead, reported in units of ppm and ppb? Pb concentration in ppm: Pb concentration in ppb: 8. If a person's tap water has a lead concentration of 8.0 ppb, and this person drinks 1.0 L of the tap water, how much lead did they consume (in units of grams)? Assume the density of the tap water is 1.0 g/mL.Explanation / Answer
Ans. #7. Mass of Pb = 0.000012 g = 0.012 mg ; [1 g = 103 mg]
= 12.0 ug ; [1 mg = 103 ug]
Mass of solution (water sample) = 1000.0 g = 1.000 kg
Now,
[Pb], ppm = Mass of Pb in mg / Mass of solution in kg
= 0.012 mg/ 1.000 kg
= 0.012 mg/ kg ; [1 mg/ kg = 1 ppm]
= 0.012 ppm
[Pb], ppb = Mass of Pb in ug / Mass of solution in kg
= 12.0 ug/ 1.000 kg
= 12.0 ug/ kg ; [1 ug/ L = 1 ppb]
= 12.0 ppb
#8. 8.0 ppb = 8.0 ug Pb / kg of water
Mass of water consumed = Volume x Density
= 1000.0 mL x (1.0 g/ mL)
= 1000.0 g
= 1.000 kg
Now,
Amount of Pb consumed = [Pb] x Volume of solution in liters
= (8.0 ug / kg) x 1.0 kg
= 8.0 ug
= 8.0 x 10-3 mg
= 8.0 x 10-6 g