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?
Ch.18 - Chemistry of the Environment
Chapter 18, Problem 78a
The estimated average concentration of NO2 in air in the United States in 2006 was 0.016 ppm. (a) Calculate the partial pressure of the NO2 in a sample of this air when the atmospheric pressure is 755 torr (99.1 kPa).
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Convert the concentration of NO_2 from parts per million (ppm) to a fraction. Since 1 ppm is equivalent to 1 part in 1,000,000 parts, 0.016 ppm is equivalent to 0.016/1,000,000.
Calculate the mole fraction of NO_2 in the air. The mole fraction is the same as the fraction of NO_2 in the air, which is 0.016/1,000,000.
Use Dalton's Law of Partial Pressures, which states that the partial pressure of a gas in a mixture is equal to the mole fraction of the gas multiplied by the total pressure of the mixture.
Multiply the mole fraction of NO_2 by the total atmospheric pressure (755 torr) to find the partial pressure of NO_2 in torr.
If needed, convert the partial pressure from torr to other units such as kPa by using the conversion factor: 1 atm = 101.325 kPa = 760 torr.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Partial Pressure
Partial pressure refers to the pressure exerted by a single component of a gas mixture. It can be calculated using Dalton's Law, which states that the total pressure of a gas mixture is equal to the sum of the partial pressures of its individual gases. In this context, the partial pressure of NO2 can be determined by multiplying its concentration (in ppm) by the total atmospheric pressure.
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Concentration Units
Concentration can be expressed in various units, including parts per million (ppm), which indicates the number of parts of a substance in one million parts of the total solution or mixture. To convert ppm to a more usable form for calculations, it is often necessary to relate it to the total pressure of the gas mixture, allowing for the determination of the partial pressure of the specific gas.
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Gas Laws
Gas laws describe the behavior of gases under various conditions of temperature, volume, and pressure. The ideal gas law (PV=nRT) is particularly relevant, as it relates pressure (P), volume (V), and temperature (T) to the number of moles (n) of gas. Understanding these laws is essential for calculating the behavior of gases in different scenarios, including determining partial pressures from concentrations.
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Related Practice
Textbook Question
(b) Concentrations of lead in the bloodstream are often quoted in units of μg/dL. Averaged over the entire country, the mean concentration of lead in the blood was measured to be 1.6 μg/dL in 2008. Express this concentration in ppb.
Textbook Question
In 1986 an electrical power plant in Taylorsville, Georgia, burned 8,376,726 tons of coal, a national record at that time. (a) Assuming that the coal was 83% carbon and 2.5% sulfur and that combustion was complete, calculate the number of tons of carbon dioxide and sulfur dioxide produced by the plant during the year.
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Textbook Question
In 1986 an electrical power plant in Taylorsville, Georgia, burned 8,376,726 tons of coal, a national record at that time. (b) If 55% of the SO2 could be removed by reaction with powdered CaO to form CaSO3, how many tons of CaSO3 would be produced?
Textbook Question
The water supply for a midwestern city contains the following impurities: coarse sand, finely divided particulates, nitrate ions, trihalomethanes, dissolved phosphorus in the form of phosphates, potentially harmful bacterial strains, dissolved organic substances. Which of the following processes or agents, if any, is effective in removing each of these impurities: coarse sand filtration, activated carbon filtration, aeration, ozonization, precipitation with aluminum hydroxide?
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