Chapter 20

Which of the following atmospheric gases is present in highest concentration in dry air? (a) \(\mathrm{N}_{2} \mathrm{O}\) (b) \(\mathrm{CH}_{4}\) (c) \(O_{3}\) (d) \(\mathrm{CO}\)

Many chemical reactions that occur in the atmosphere and stratosphere involve free radicals. Free radical formation occurs when a photon of light is absorbed and the energy of the radiation being absorbed causes a chemical bond in the compound to break. Which of the following bonds requires the most energy (and the most energetic radiation) to be broken? (a) The oxygen-oxygen bond in \(\mathrm{O}_{2}\) (b) The chlorine-carbon bond in \(\mathrm{CCl}_{2} \mathrm{F}_{2}\) (c) The oxygen-oxygen bond in \(\mathrm{O}_{3}\)

Assume the average \(\mathrm{CO}_{2}\) concentration in the atmosphere is 406 ppm (as of January 2017 ). The actual concentration of \(\mathrm{CO}_{2}\) at different sites will vary. Speculate on whether the concentration of \(\mathrm{CO}_{2}\) would be expected to be higher, lower, or the same as this average value in a typical large city.

Suppose you find the CO concentration in your home is \(10 .\) ppm by volume at 1.00 atm pressure and \(25^{\circ} \mathrm{C} .\) What is the CO concentration in \(\mathrm{mg} / \mathrm{L}\) and in ppm by mass. (The average molar mass for dry air is \(28.96 \mathrm{g} / \mathrm{mol}\) at 1.00 atm pressure and \(\left.25^{\circ} \mathrm{C} .\right)\)

Various reagents are added to water supplies to kill pathogens and make the water safe to drink. Among the substances listed below, which does not serve that function? (a) \(\mathrm{Cl}_{2}\) (b) \(\mathrm{O}_{3}\) (c) \(\mathrm{Ca}(\mathrm{ClO})_{2}\) (d) \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\)

Which of the following statements is not correct? (a) Phosphates enhance the growth of algae in surface water. (b) Melting of the polar ice cap will result in a rise in sea levels. (c) Heavy metal toxicity can result from the presence of metal compounds of lead, cadmium, and mercury in water supplies. (d) Reverse osmosis is a good way to effect desalination.

Although there are a number of magnesiumcontaining minerals, the commercial source of this metal is seawater. Treatment of seawater with \(\mathrm{Ca}(\mathrm{OH})_{2}\) gives insoluble \(\mathrm{Mg}(\mathrm{OH})_{2} .\) This reacts with HCl to produce \(\mathrm{MgCl}_{2}\), which is dried, and the metal is obtained by electrolysis of the molten salt. Write balanced net ionic equations for the three reactions described here.

A 2010 article in Science magazine described "Sewage Treatment with Anammox." IB. Kartal, I. G. Kuenen, and M. C. M. van Loosdrecht, Science, Vol. \(328,\) pp. \(702-703,2010 .\) The authors noted that "Fixed nitrogen such as ammonium and nitrate [ions] must be removed [from sewage] to avoid toxic algal blooms in the environment." One approach to removing ammonium ions is to use ammonium-oxidizing (anammox) bacteria. Two (unbalanced) reactions that are involved are: $$\begin{array}{l}\mathrm{NH}_{4}^{+}(\mathrm{aq})+\mathrm{NO}_{2}^{-}(\mathrm{aq}) \rightarrow \mathrm{N}_{2}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\ell) \\\\\mathrm{NH}_{4}^{+}(\mathrm{aq})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{NO}_{2}^{-}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)\end{array}$$ Balance these two equations in acid solution.

Which of the following is a renewable energy resource? (a) nuclear fusion (b) hydroelectric power (c) natural gas (d) coal

In the United States (and worldwide), fossil fuels provide the larger source of energy. What is the second largest energy source? (a) hydroelectric (b) solar (c) nuclear (d) geothermal

The enthalpy of combustion of isooctane \(\left(\mathrm{C}_{8} \mathrm{H}_{18}\right)\) one of the many hydrocarbons in gasoline, is \(5.45 \times 10^{3} \mathrm{kJ} / \mathrm{mol} .\) Calculate the enthalpy change per gram of isooctane and per liter of isooctane \((d=0.688 \mathrm{g} / \mathrm{mL})\)

Calculate the energy used, in kilojoules, to power a 100-watt lightbulb continuously over a 24 -hour period. How much coal would have to be burned to provide this quantity of energy, assuming that the enthalpy of combustion of coal is \(33 \mathrm{kJ} / \mathrm{g}\) and the power plant has an efficiency of \(35 \% ?\) [ Electrical energy for home use is measured in kilowatt hours (kW-h). One watt is defined as \(1 \mathrm{J} / \mathrm{s},\) and \(1 \mathrm{kW}\) -h is the quantity of energy transferred when 1000 watt is dispensed over a 1.0 -hour period.

A parking lot in Los Angeles receives an average of \(2.6 \times 10^{7} \mathrm{J} / \mathrm{m}^{2}\) of solar energy per day in the summer. (a) If the parking lot is \(325 \mathrm{m}\) long and \(50.0 \mathrm{m}\) wide, what is the total quantity of energy striking the area per day? (b) What mass of coal would have to be burned to supply the quantity of energy calculated in (a)? (Assume the enthalpy of combustion of coal is \(33 \mathrm{kJ} / \mathrm{g} .)\)

Your home loses energy in the winter through doors, windows, and any poorly insulated walls. A sliding glass door \((6 \mathrm{ft} \times 6.5 \mathrm{ft} \text { with } 0.5\) inch of insulating glass ) allows \(1.0 \times 10^{6} \mathrm{J} / \mathrm{h}\) to pass through the glass if the inside temperature is \(22^{\circ} \mathrm{C}\left(72^{\circ} \mathrm{F}\right)\) and the outside temperature is \(0^{\circ} \mathrm{C}\left(32^{\circ} \mathrm{F}\right) .\) What quantity of energy, expressed in kilojoules, is lost per day? Assume that your house is heated by electricity. How many kilowatt-hours of energy are lost per day through the door? (See Study Question 24 for the definition of a kilowatt- hour.

Some fuel-efficient hybrid cars are rated at 55.0 miles per gallon of gasoline. Calculate the energy used to drive 1.00 mile if gasoline produces \(48.0 \mathrm{kJ} / \mathrm{g}\) and the density of gasoline is \(0.737 \mathrm{g} / \mathrm{cm}^{3} .(1.00 \mathrm{gal}=3.785 \mathrm{L})\)

Microwave ovens are highly efficient, compared to other cooking appliances. A 1100 -watt microwave oven, running at full power for 90 seconds, will raise the temperature of 1 cup of water \((225 \mathrm{mL})\) from \(20^{\circ} \mathrm{C}\) to \(67^{\circ} \mathrm{C} .\) As a rough measure of the efficiency of the microwave oven, compare its energy consumption with the energy required to raise the water temperature.

Which of the following is not a limitation for the use of hydrogen as a fuel? (a) An inexpensive method of producing hydrogen (b) A practical means of storing hydrogen (c) Hydrogen is explosive (d) A distribution system (hydrogen refueling stations)

Which of the following statements is true? (a) Fuel cells are widely used in automobiles. (b) \(\mathrm{H}_{2}\) is readily available as a transportation fuel. (c) Petroleum is a mixture of hydrocarbons. (d) Methane hydrate can never be developed as a commercial energy resource.

Which of the species listed below is not a greenhouse gas? (a) \(\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{CH}_{4}\) (c) \(\mathrm{CO}_{2}\) (d) \(\mathrm{O}_{2}\)

What is the correlation between ocean \(\mathrm{pH}\) and atmospheric \(\mathrm{CO}_{2} ?\) (a) As \(\mathrm{CO}_{2}\) increases, the pH decreases. (b) As \(\mathrm{CO}_{2}\) increases, the pH also increases. (c) As \(\mathrm{CO}_{2}\) increases, the pH does not change.

Dinitrogen monoxide, \(\mathrm{N}_{2} \mathrm{O}\) (commonly called nitrous oxide), is prepared by the careful decomposition of ammonium nitrate and is used as an oxidizing agent in rocket engines as well as a weak general anesthetic (where you may know it as "laughing gas".). However, it is also known to be a powerful greenhouse gas. In a Science magazine article, it was stated that "Human activities may be causing an unprecedented rise in the terrestrial \(\mathrm{N}_{2} \mathrm{O}\) source. Marine \(\mathrm{N}_{2} \mathrm{O}\) production may also rise substantially as result of eutrophication, warming, and ocean acidification." \([\mathrm{L} . \text { A. Codispoti, } \text {Science}\), Vol. \(327, \text { pp. } 1339-1340,2010 .]\) (a) Draw a Lewis electron dot structure for \(\mathrm{N}_{2} \mathrm{O}\) and specify the formal charge on each atom and the molecular geometry. (b) The atom connections are \(\mathrm{N}-\mathrm{N}-\mathrm{O} .\) Why is the connection \(\mathrm{N}-\mathrm{O}-\mathrm{N}\) not likely? (c) The highest \(\mathrm{N}_{2} \mathrm{O}\) concentration observed in the ocean is about 800 nM (nanomolar). At this concentration, what is the mass of \(\mathrm{N}_{2} \mathrm{O}\) per liter?

In \(2005,\) global \(\mathrm{SO}_{2}\) emission was estimated to be \(12.83 \mathrm{Gg}\) (gigagrams). According to the \(\mathrm{EPA}, 71 \%\) of \(\mathrm{SO}_{2}\) emissions into the atmosphere is from coal-fired power plants. How much coal (in metric tons) must have been burned to produce this much \(\mathrm{SO}_{2}\) assuming that coal is \(2.0 \%\) sulfur?

The refrigerating liquids in air conditioners and refrigerators are largely chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Among the latter family of compounds is the refrigerant HCFC-22 \(\left(\mathrm{HCClF}_{2}\right)\). A problem with the use of HCFC-22 is that HFC-23 (trifluoromethane, HCF \(_{3}\) ), a gas with high-global-warming potential, is a byproduct of its production (and also from the production of the widely used polymer Teflon). Discarding HFC-23 safely can be a problem. However, recently a method has been developed to convert it to the valuable catalyst trifluoromethanesulfonic acid, \(\mathrm{CF}_{3} \mathrm{SO}_{3} \mathrm{H}\). Draw an electron dot structure for the acid (which you can think of as sulfuric acid with a \(\mathrm{CF}_{3}\) group in place of one OH group). Indicate the geometry around the \(\mathrm{C}\) and \(\mathrm{S}\) atoms. What is the hybridization of these two atoms?

Chlorine atoms are formed by photochemical reactions of chlorofluorocarbons in the upper atmosphere. Using the average bond energy of the \(\mathrm{C}-\mathrm{Cl}\) bond in Table \(8.8,\) calculate the wavelength of radiation with sufficient energy to break the \(\mathrm{C}-\mathrm{Cl}\) bond. In what region of the electromagnetic spectrum does this fall?

Steps have been taken to limit phosphorus in surface water. However, the amounts of nitrogen-containing species in surface water can also be a problem because they also promote excessive growth of algae and water plants. What are likely sources of this nitrogen? What nitrogen compounds are likely to be present in surface water?

Imagine the following experiment: You have a large graduated cylinder containing 100. mL of liquid water at \(0^{\circ} \mathrm{C}\). You drop an ice cube with a volume of \(25 \mathrm{cm}^{3}\) into the cylinder. Ice has a density of \(0.92 \mathrm{g} / \mathrm{cm}^{3},\) less than the density of liquid water, so it floats with \(92 \%\) being under water. (a) To what level will the water in the graduated cylinder rise after adding the ice? (b) Allow the ice to melt. What volume will now be occupied by the liquid water? (One consequence of global warming will be a rise in sea level as ice in the northern and southern regions of the planet melts. However, the effect relates only to melting of ice on land. Melting of floating ice will have no effect on sea levels.

The mineral claudetite contains the element arsenic in the form of arsenic(III) oxide, \(A s_{2} O_{3}\). The \(A s_{2} O_{3}\) in a \(0.562-g\) sample of the impure mineral was converted first to \(\mathrm{H}_{3} \mathrm{AsO}_{3}\) and then titrated with a \(0.0480 \mathrm{M}\) solution of \(\mathrm{I}_{3}^{-},\) which reacts with \(\mathrm{H}_{3} \mathrm{AsO}_{3}\) according to the following balanced net ionic equation $$\begin{aligned}\mathrm{H}_{3} \mathrm{AsO}_{3}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{I}_{3}^{-}(\mathrm{aq}) & \rightarrow \\\\\mathrm{H}_{3} \mathrm{AsO}_{4}(\mathrm{aq}) &+2 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})+3 \mathrm{I}^{-}(\mathrm{aq})\end{aligned}$$ If the titration required \(45.7 \mathrm{mL}\) of the \(\mathrm{I}_{3}^{-}\) solution, what is the percentage of \(\mathrm{As}_{2} \mathrm{O}_{3}\) in the mineral sample?

Define the terms renewable and nonrenewable as applied to energy resources. Which of the following energy resources are renewable: solar energy, coal, natural gas, geothermal energy, wind power?

What are the three most abundant gases in the atmosphere? Are any of these greenhouse gases?

What are the environmental consequences of ozone in the troposphere? In the stratosphere?

Mercury, lead, and arsenic in the environment are major concerns. Identify the main source or sources of these pollutants.

What is the likelihood that hydrogen \(\left(\mathrm{H}_{2}\right)\) will become a widely used fuel and that the "hydrogen economy" will become a reality? In particular, what are the advantages and disadvantages of \(\mathrm{H}_{2}\) as a fuel? What would be necessary for a significant conversion to a "hydrogen economy"?

An understanding of most environmental issues requires one to consider a range of factors-economic, political, sociological, as well as scientific. Bearing this in mind, discuss each of the issues below. (a) Fracking is now in wide use, allowing us to access large quantities of natural gas. What are the positive factors that argue for continued and expanded use of this technique, and what are the concerns? (b) Most gasoline now sold contains ethanol. Is production of ethanol for use as a fuel a wise choice? List arguments for and against this policy. (c) Two types of vehicles, electric cars and cars using natural gas, are in early stages of development in the United States. Should their development be encouraged? What are the advantages and disadvantages to owning these cars now?

Which sulfur compounds are atmospheric pollutants? What is their origin? Describe steps being taken to prevent sulfur compounds from entering the atmosphere.