Multiple Choice
A water sample contains 0.005 g of sodium (Na) in 1.0 L of water. What is the concentration of sodium 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
17.1 mg
B
0.171 mg
C
1.22 mg
D
12.2 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: \(\text{mass in kg} = \frac{1400\, \text{g}}{1000}\).
Use the ppm definition to set up a proportion: \(\frac{12.2\, \text{mg Hg}}{1\, \text{kg water}} = \frac{x\, \text{mg Hg}}{\text{mass of sample in kg}}\) where \(x\) is the mass of Hg in the sample.
Solve for \(x\) by multiplying the ppm value by the mass of the sample in kilograms: \(x = 12.2 \times \text{mass in kg}\).
Express the final answer in milligrams (mg), which is the unit consistent with ppm, to find the mass of mercury in the 1400 g water sample.
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