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

Answer: (A)

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. 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.
4. Solve for \(x\) by multiplying the ppm value by the mass of the sample in kilograms: \(x = 12.2 \times \text{mass in kg}\).
5. 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.