Chapter 2 Problems and Answers
4. The concentration of argon in air is approximately 0.934%. Express this value in ppm.
1%= 10,000 ppm 0.934%= (x)ppm x= 0.934% x 10,000ppm/1% x=9,340ppm
13. Balance the following equations in which ethane burns in oxygen. a. C2H6(g) + O2(g) ---> C(s) + H2O(g) b. C2H6(g) + O2(g) ---> CO(g) + H2O(g) c. C2H6(g) + O2(g) ---> CO2(g) + H2O(g) d. Explain why the coefficients for oxygen vary, depending on whether Cm CO, or CO2 is formed.
a) 2 C2H6(g) + 3 O2(g) = 4 C(s) + 6 H2O(g) b) 2 C2H6(g) + 5 O2(g) = 4 CO(g) + 6 H2O(g) c) 2 C2H6(g) + 7 O2(g) = 4 CO2(g) + 6 H2O(g) d) The balanced equations show that complete combustion requires the highest ratio of oxygen to ethane 7:2. If a 5:2 ratio is present, carbon monoxide is formed instead of carbon dioxide. If its a 3:2 ratio, then carbon is formed.
3. Identify three sources of particulate matter found in air. Explain the difference between PM2.5 and PM10 in terms of size and health effects.
Atmospheric particulate matter is microscopic solid or liquid matter suspended in the Earth's atmosphere. The sources of these can be natural (volcanoes, dust storms, forest fires etc) as well as man-made (burning of fossil fuels in vehicles, power plants and other industries.)' The particulate matter is classified on the basis of their size. Size, in turn, means the diameter of the dust particulates in terms of microns (i.e. µm which is basically a millionth of a meter.) Coarse dust particles (PM10) are 2.5 to 10 micrometers in diameter. Sources include crushing or grinding operations and dust stirred up by vehicles on roads. These tiny particles which are about 30 times smaller than the width of a hair on your head are small enough to get inhaled past our defensive nose hairs and into our lungs. Fine particles (PM2.5) are 2.5 micrometers in diameter or smaller, and can only be seen with an electron microscope. Fine particles are produced from all types of combustion, including motor vehicles, power plants, residential wood burning, forest fires, agricultural burning, and some industrial processes. While PM10's story ends at the lungs, PM2.5 can pass from our lungs into our blood supply and be carried throughout our bodies thereby making them "the invisible killer"
31. In the Northern Hemisphere, the ozone season runs from about May 1 to October 1. Why are ozone levels typically not reported in the winter months?
The ozone levels are not reported in the winter because of the differences in the sunlight between the summer and the winter. Even at its greatest winter intensity, the sunlight is much less intense. Sunlight is needed to produce ozone.
34. Here are air quality data for the last week of 2015, in Beijing, China, for air quality based on the primary pollutant of PM2.5 a) In general, which groups of people are the most sensitive to particulate matter? b) The U.S Environmental Protection Agency determined that air rated between 51-100 is acceptable except for particularly sensitive groups. For the data shown, when was the air acceptable or better? c) The levels of PM do now necessarily drop off at night the way they do for ozone. Explain. d) The levels of particulate matter can increase sharply. Propose two different reasons that could account for this observation.
a) In short-term studies, elderly people and those with pre-existing heart and lung disease were found to be more susceptible to effects of ambient PM on mortality and morbidity. In panel studies, asthmatics have also been shown to be more vulnerable to ambient PM compared to non-asthmatics. Responses of asthmatics to PM exposure include increased symptoms, larger lung function changes, and increased medication use. b) It was acceptable Dec 21-22, Dec 27th, and Dec 31st. c) Although PM varies in composition, most of it is less chemically active than the ozone. It typically is removed from the air by rain or wind. d) Possibilities include smoke blowing in from a wildfire, an air inversion, large industrial releases of soot, and volcanic eruption somewhere in the region that released the ash and soot.
10. Consider this representation of the reaction between nitrogen and hydrogen to form ammonia NH3. (Illustration in book, p. 74) a) Are the masses of reactants and products the same? Explain. b) Are the numbers of molecules of reactants and of products the same? Explain c) Are the total number of atoms in the reactants and the total number of atoms in the products the same? Explain.
a) In the reaction masses of the reactants and products are the same N2 + 3 H2 ---> 2 NH3 The reactant side contains two nitrogen atoms and six hydrogen atoms. After the reaction the product contains two molecules of ammonia (2 NH3), which is composed of the same amount of nitrogen and hydrogen as the reactant side. b) Heres the steps to get to the answer: Step 1: Write the chemical formula Step 2: List all the atoms Step 3: Count the number of atoms of each element in 1 molecule. Step 4: Multiply the number of atoms of each by the coefficient. -coefficient ratio of H2 to N2 (3:1) -coefficient ratio of NH3 to H2, which is 2:3 Answer: No, the numbers of molecules are not the same. There are four reactant molecules vs. two product molecules. c) Yes, the number of atoms on both reactant and product side are the same.
27. A headline from the Anchorage Daily News in Alaska: "Family in car overcome by carbon monoxide. Fire department saves five after slide into snow bank." a) If your car is in the snow bank and the engine is running, CO may accumulate inside your car. Normally, however, CO does not accumulate in the car. Explain. b) Why didn't the occupants detect the CO?
a) Normally, the exhaust gases are released to the atmosphere through the exhaust pipe and don't find their way back into the interior of the car. The exhaust does not have a connection to the interior. However, if the gases are released into an enclosed space like a snow bank, they may seep back into the car as there is no easy escape path into the wider environment. b. CO is an odorless, colorless, and tasteless gas b) Because CO is odorless, and tasteless the occupants were not able to detect that they were breathing in CO.
21. Sulfur dioxide and nitrogen dioxide are considered to be air pollutants. a) where would you most likely find these pollutants? b) Which of these pollutants is more toxic c) Express 0.045 ppm nitrogen dioxide in ppb.
a) The most important sources of SO2 are fossil fuel combustion, smelting, manufacture of sulphuric acid, conversion of wood pulp to paper, incineration of refuse and production of elemental sulphur. Coal burning is the single largest man-made source of SO2 accounting for about 50% of annual global emissions, with oil burning accounting for a further 25-30%. Globally, quantities of nitrogen oxides produced naturally (by bacterial and volcanic action and lightning) far outweigh anthropogenic (man-made) emissions. Anthropogenic emissions are mainly due to fossil fuel combustion from both stationary sources, i.e. power generation (21%), and mobile sources, i.e. transport (44%). Other atmospheric contributions come from non-combustion processes, for example nitric acid manufacture, welding processes and the use of explosives. b) They are both toxic, but sulfur dioxide is more harmful. (I'm not sure if I have this right) c) 1ppm = 1/106 = 10-6 1ppm = 1000ppb 0.045ppm=45ppb
41. a)Explain why running outdoors (as opposed to sitting outdoors) increases your exposure to pollutants. b) Running indoors at home can decrease your exposure to some pollutants, but may increase your exposure to others. Explain.
a) While aerobic activity is one of the keys to a healthy lifestyle, air pollution and exercise can be an unhealthy combination. This is especially true if you have asthma, diabetes, or heart or lung conditions. One reason for this increased risk may be that during aerobic activity, you usually inhale more air and breathe it more deeply into your lungs. And because you're more likely to breathe deeply through your mouth during exercise, the air you breathe in generally bypasses your nasal passages, which normally filter airborne pollution particles. b) For what it's worth, heading indoors isn't necessarily a solution. New carpets, ski wax, Zambonis, and even candles and incense in a yoga studio can all compromise air quality. You can minimize your exposure to these sources with a little planning, but it's another reason not to shy away from heading outside.
6. Hydrocarbons are important fuels that we burn primarily for energy. a) What is a hydrocarbon? b) Rank the following hydrocarbons by the number of carbons they contain from smallest to largest: pentane, ethane, octane, hexane, propane. c) We suggested "mother eats peanut butter" as a memory aid for the names of the first four hydrocarbons by number of carbon atoms. Propose a new one that includes pent-, the prefix that indicated five carbon atoms.
a) a compound of hydrogen and carbon, such as any of those that are the chief components of petroleum and natural gas. b) Octane- 8 Hexane- 6 Pentane-5 Propane- 3 Ethane- 2 c) My eggs probably busted, perhaps hay. (Methane, Ethane, Propane, Butane, Pentane, Hexane)
