Textbook Question
(a) The EPA threshold for acceptable levels of lead ions in water is 615 ppb. What is the molarity of an aqueous solution with a concentration of 15 ppb?
14. Solutions
Parts per Million (ppm)
Multiple Choice
A water sample is found to contain the pollutant chlorobenzene with a concentration of 15 ppb (by mass). What volume of this water contains 5.00 × 10² mg of chlorobenzene? (Assume a density of 1.00 g/mL.)
A
3.33 L
B
33.3 L
C
0.333 L
D
333 L
Verified step by step guidance1
Understand that ppb (parts per billion) is a unit of concentration that represents the mass of solute per billion parts of the solution. In this case, 15 ppb means 15 grams of chlorobenzene per 1 billion grams of water.
Convert the concentration from ppb to a more usable unit. Since 1 ppb is equivalent to 1 microgram per liter (µg/L) when the density of water is 1 g/mL, 15 ppb is equivalent to 15 µg/L.
Convert the mass of chlorobenzene from milligrams to micrograms to match the concentration units. Since 1 mg = 1000 µg, 5.00 × 10² mg is equal to 5.00 × 10⁵ µg.
Use the concentration to find the volume of water needed. Set up the equation: \( \text{Volume of water (L)} = \frac{\text{mass of chlorobenzene (µg)}}{\text{concentration (µg/L)}} \). Substitute the known values: \( \text{Volume of water (L)} = \frac{5.00 \times 10^5 \text{ µg}}{15 \text{ µg/L}} \).
Solve the equation to find the volume of water in liters. This will give you the volume of water that contains 5.00 × 10² mg of chlorobenzene.
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