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

Answer: (C)

Verified step by step guidance

1. 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.
2. Convert the mass of the water sample from grams to kilograms by dividing by 1000: \(\text{mass in kg} = \frac{1400\, \text{g}}{1000}\).
3. Set up a proportion to find the mass of mercury in the 1400 g sample using the ppm definition: \(\frac{12.2\, \text{mg Hg}}{1\, \text{kg water}} = \frac{x\, \text{mg Hg}}{1.4\, \text{kg water}}\).
4. 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.
5. The result from step 4 gives the mass of mercury present in the 1400 g water sample.