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ANSWERS TO  END-OF-CHAPTER QUESTIONS CHAPTER 1: THE AIR WE BREATHE Emphasizing Essentials 1. Calculate the volume of air that an adult person exhales in an 8-hour day. Assume that each breath has a volume of about 0.5 L and that the person exhales 15 times a minute. Answer: 0 .5L 1breath × 15breaths 1m in × 60m in 1hr × 8hr 1workingday = 3600L 2. Given that dry air is 78% nitrogen by volume, how many liters of nitrogen are in 500 L? Answer: 78 L nitrogen 100 L air × 500L air = 390 L nitrogen 3. A 5.0-L mixture of gases is prepared for a study of photosynthesis by combining 0.75 L of oxygen, 4.0 L of nitrogen, and 0.25 L of carbon dioxide. Compare the percentage of carbon dioxide gas in this mixture with that normally found in the atmosphere. Answer: 0 .25Lcarbondioxide 5 .0Lm ixture × 100 = 5%carbondioxidebyvolume Note: This is considerably higher than the 0.04% by volume commonly found in dry air. 4. Give three examples of particulate matter found in air. What is the difference between PM 2.5 and PM 10 in terms of their size? In terms of their health effects? Answer: Examples of particulate matter found in air include dust, soot, dirt, microscopic droplets of liquid, bacteria, and viruses. PM 2.5 and PM 10 differ in size. The former has particles 2.5μm or less in diameter; the latter 10μm or less. The smaller particles are more damaging to human health. 5. These gases are found in the troposphere: Rn, CO 2 , CO, O 2 , Ar, and N 2 . a. Rank them in order of their abundance in the troposphere. b. The concentration of one or more of these gases is more conveniently expressed in parts per million. Which one(s)? c. One or more of these gases is a criteria air pollutant. Which one(s)? d. One or more of these is a noble gas (Group 8A). Which one(s)? PAGE 1- 1
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Answer: a. Ranked in order of abundance in the troposphere: N 2 > O 2 > Ar > CO 2 > CO > Rn. b. It is more convenient to express the concentrations of CO 2 and CO in ppm. c. Only CO is a criteria air pollutant. d. Rn (radon) is a noble gas. 6. a. The concentration of argon in air is approximately 9000 ppm. Express this value as a percent. b. The smoke inhaled from a cigarette contains 0.04–0.05% CO. Express these concentrations in parts per million. c. The concentration of water vapor in the atmosphere of a tropical rain forest may reach 50,000 ppm. Express this value as a percentage. Answer: a. 9000 ppm × 100 parts per hundred 1 ,000 ,000 ppm = 0 .9 parts per hundred or 0 .9% b. 0 .04 parts per hundred × 1 ,000 ,000 parts per m illion 100 parts per hundred = 400 parts per m illion c. 50 ,000 ppm × 100 parts per hundred 1 ,000 ,000 ppm = 5 parts per hundred or 5% Be careful not to confuse the absolute humidity calculated in this problem with relative humidity, which is the amount of water vapor in the air compared to the maximum possible amount of water vapor that the air can hold at a particular temperature. In a rainforest, the relative humidity is usually between 75 and 95%. 7.
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This note was uploaded on 01/12/2011 for the course CHEM 100 taught by Professor Staff during the Spring '08 term at Ohio State.

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