Multiple Choice
Amphetamines in urine can be confirmed by mass spectrometry at a concentration of 500 ng/mL. Assuming a urine density of 1.025 g/mL, what is this concentration in parts per million (ppm)?
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14. Solutions
Parts per Million (ppm)
Multiple Choice
A 1400 g sample of stream water contains 12.2 ppm of mercury (Hg). What is the mass of Hg present in the sample?
A
12.2 mg
B
0.171 mg
C
17.1 mg
D
1.22 mg
Verified step by step guidance1
Understand that ppm (parts per million) means milligrams of solute per kilogram of solution. So, 12.2 ppm of mercury means 12.2 mg of Hg per 1 kg of water.
Convert the mass of the water sample from grams to kilograms by dividing by 1000: \(\text{mass in kg} = \frac{1400\, \text{g}}{1000}\).
Set up a proportion to find the mass of mercury in the 1400 g sample using the ppm definition: \(\frac{12.2\, \text{mg Hg}}{1\, \text{kg water}} = \frac{x\, \text{mg Hg}}{1.4\, \text{kg water}}\).
Solve for \(x\), the mass of mercury in mg, by multiplying 12.2 mg by the mass of the sample in kg: \(x = 12.2 \times 1.4\) mg.
The result from step 4 gives the mass of mercury present in the 1400 g water sample.
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