Chemistry: The Central Science in SI Units, Global Edition

Theodore L. Brown, Matthew W. Stoltzfus, Michael W. Lufaso

Chapter 18

Chemistry of the Environment - all with Video Answers

Educators

Chapter Questions

Problem 1

At $273 \mathrm{~K}$ and $101.3 \mathrm{kPa}, 1 \mathrm{~mol}$ of an ideal gas occupies 22.4 L. (Section 10.4 ) (a) Looking at Figure 18.1, predict whether a $1 \mathrm{~mol}$ sample of the atmosphere in the middle of the stratosphere would occupy a greater or smaller volume than $22.4 \mathrm{~L}(\mathbf{b})$ Looking at Figure $18.1,$ we see that the temperature is lower at $85 \mathrm{~km}$ altitude than at $50 \mathrm{~km}$. Does this mean that one mole of an ideal gas would occupy less volume at $85 \mathrm{~km}$ than at $50 \mathrm{~km}$ ? Explain. (c) In which parts of the atmosphere would you expect gases to behave most ideally (ignoring any photochemical reactions)? [Section 18.1]

Crystal Wang

Crystal Wang

Numerade Educator

Problem 2

Molecules in the upper atmosphere tend to contain double and triple bonds rather than single bonds. Suggest an explanation. [Section 18.1]

James Irizarry

Numerade Educator

Problem 3

The figure shows the three lowest regions of Earth's atmosphere. (a) Name each and indicate the approximate elevations at which the boundaries occur. (b) In which region is ozone a pollutant? In which region does it filter UV solar radiation? (c) In which region is infrared radiation from Earth's surface most strongly reflected back? (d) An aurora borealis is due to excitation of atoms and molecules in the atmosphere $55-95 \mathrm{~km}$ above Earth's surface. Which regions in the figure are involved in an aurora borealis? (e) Compare the changes in relative concentrations of water vapor and carbon dioxide with increasing elevation in these three regions [Section 18.1].

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 4

You are working with an artist who has been commissioned to make a sculpture for a big city in the eastern United States. The artist is wondering what material to use to make her sculpture because she has heard that acid rain in the eastern United States might destroy it over time. You take samples of granite, marble, bronze, and other materials, and place them outdoors for a long time in the big city. You periodically examine the appearance and measure the mass of the samples. (a) What observations would lead you to conclude that one or more of the materials are wellsuited for the sculpture? (b) What chemical process (or processes) is (are) the most likely responsible for any observed changes in the materials? [Section 18.2$]$

Crystal Wang

Numerade Educator

Problem 5

Where does the energy come from to evaporate the estimated $425,000 \mathrm{~km}^{3}$ of water that annually leaves the oceans, as illustrated here? [Section 18.3]

Kevin Chimex

Numerade Educator

Problem 6

The Earth's oceans have a salinity of $35 .$ What is the concentration of dissolved salts in seawater when expressed in ppm? What percentage of salts must be removed from seawater before it can be considered freshwater (dissolved salts $<500 \mathrm{ppm}) ?[$ Section 18.3$]$

Crystal Wang

Numerade Educator

Problem 7

Describe what changes occur when atmospheric $\mathrm{CO}_{2}$ interacts with the world ocean as illustrated here. [Section 18.3]

Kevin Chimex

Numerade Educator

Problem 8

The first stage of treatment at the reverse osmosis plant in Carlsbad, California, is to flow the water through rock, sand, and gravel as shown here. Would this step remove particulate matter? Would this step remove dissolved salts? [Section 18.4]

James Irizarry

Numerade Educator

Problem 9

From study of Figure 18.23 describe the various ways in which operation of a fracking well site could lead to environmental contamination.

Kevin Chimex

Numerade Educator

Problem 10

One mystery in environmental science is the imbalance in the "carbon dioxide budget." Considering only human activities, scientists have estimated that 1.6 billion metric tons of $\mathrm{CO}_{2}$ is added to the atmosphere every year because of deforestation (plants use $\mathrm{CO}_{2},$ and fewer plants will leave more $\mathrm{CO}_{2}$ in the atmosphere). Another 5.5 billion tons per year is put into the atmosphere because of burning fossil fuels. It is further estimated (again, considering only human activities) that the atmosphere actually takes up about 3.3 billion tons of this $\mathrm{CO}_{2}$ per year, while the oceans take up 2 billion tons per year, leaving about 1.8 billion tons of $\mathrm{CO}_{2}$ per year unaccounted for. Describe a mechanism by which $\mathrm{CO}_{2}$ is removed from the atmosphere and ultimately ends up below the surface (Hint: What is the source of the fossil fuels?). [Sections $18.1-18.3]$

James Irizarry

Numerade Educator

Problem 11

(a) What is the primary basis for the division of the atmosphere into different regions?
(b) Name the regions of the atmosphere, indicating the altitude interval for each one.

Kevin Chimex

Numerade Educator

Problem 12

(a) How are the boundaries between the regions of the atmosphere determined?
(b) Explain why the stratosphere, which is about $35 \mathrm{~km}$ thick, has a smaller total mass than the troposphere, which is about $12 \mathrm{~km}$ thick.

James Irizarry

Numerade Educator

Problem 13

The Environmental Protection Agency (EPA) has established air quality standards. For ozone $\left(\mathrm{O}_{3}\right),$ the 8 -hour average concentration permitted under the standards is 0.085 parts per million (ppm). (a) Calculate the partial pressure of ozone at 0.085 ppm if the atmospheric pressure is $100 \mathrm{kPa}$. (b) How many ozone molecules are in $1.0 \mathrm{~L}$ of air? Assume $T=25^{\circ} \mathrm{C}$.

Crystal Wang

Numerade Educator

Problem 14

From the data in Table 18.1, calculate the partial pressures of neon and helium when the total atmospheric pressure is $102.3 \mathrm{kPa}$.

Crystal Wang

Numerade Educator

Problem 15

The average concentration of carbon monoxide in air in a city in 2007 was 3.0 ppm. Calculate the number of CO molecules in $1.0 \mathrm{~L}$ of this air at a pressure of $100 \mathrm{kPa}$ and a temperature of $25^{\circ} \mathrm{C}$.

Crystal Wang

Numerade Educator

Problem 16

(a) From the data in Table 18.1, what is the concentration of helium in the atmosphere in ppm?
(b) What is the concentration of helium in the atmosphere in atoms per liter, assuming an atmospheric pressure of $101 \mathrm{kPa}$ and a temperature of $298 \mathrm{~K} ?$

Crystal Wang

Numerade Educator

Problem 17

The dissociation energy of a carbon-iodine bond is typically about $240 \mathrm{~kJ} / \mathrm{mol} .(\mathbf{a})$ What is the maximum wavelength of photons that can cause $\mathrm{C}-\mathrm{I}$ bond dissociation?
(b) Which kind of electromagnetic radiation-ultraviolet, visible, or infrared-does the wavelength you calculated in part (a) correspond to?

Crystal Wang

Numerade Educator

Problem 18

In $\mathrm{CH}_{3} \mathrm{I}$ the $\mathrm{C}$ - I bond-dissociation energy is $241 \mathrm{~kJ} / \mathrm{mol}$. In $\mathrm{C}_{6} \mathrm{H}_{5}$ I the $\mathrm{C}-$ I bond-dissociation energy is $280 \mathrm{~kJ} / \mathrm{mol}$. What is the range of wavelengths of photons that can cause $\mathrm{C}-\mathrm{I}$ bond rupture in one molecule but not in the other?

Crystal Wang

Numerade Educator

Problem 19

(a) Distinguish between photodissociation and photoionization.
(b) Use the energy requirements of these two processes to explain why photodissociation of oxygen is more important than photoionization of oxygen at altitudes below about $90 \mathrm{~km}$.

Kevin Chimex

Numerade Educator

Problem 20

Why is the photodissociation of $\mathrm{N}_{2}$ in the atmosphere relatively unimportant compared with the photodissociation of $\mathrm{O}_{2} ?$

James Irizarry

Numerade Educator

Problem 21

The dissociation energy of $\mathrm{N}_{2}$ is very high, $941 \mathrm{~kJ} / \mathrm{mol}$. (a) Calculate the wavelength of the photons that possess sufficient energy to dissociate $\mathrm{N}_{2} .(\mathbf{b})$ In which region of the electromagnetic spectrum does this light fall? Does this light have enough energy to photoionize $\mathrm{N}_{2}$ ?

Crystal Wang

Numerade Educator

Problem 22

The ultraviolet spectrum can be divided into three regions based on wavelength: UV-A (315-400 nm), UV-B (280-315 $\mathrm{nm})$, and UV-C $(100-280 \mathrm{nm})$. (a) Photons from which region have the highest energy and therefore are the most harmful to living tissue? (b) In the absence of ozone, which of these three regions, if any, are absorbed by the atmosphere? (c) When appropriate concentrations of ozone are present in the stratosphere, is all of the UV light absorbed before reaching the Earth's surface? If not, which region or regions are not filtered out?

James Irizarry

Numerade Educator

Problem 23

Do the reactions involved in ozone depletion involve changes in oxidation state of the O atoms? Explain.

Kevin Chimex

Numerade Educator

Problem 24

Which of the following reactions in the stratosphere cause an increase in temperature there?
(a) $\mathrm{O}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{O}_{3}^{*}(g)$
(b) $\mathrm{O}_{3}^{*}(g)+\mathrm{M}(g) \longrightarrow \mathrm{O}_{3}(g)+\mathrm{M}^{*}(g)$
(c) $\mathrm{O}_{2}(g)+h \nu \longrightarrow 2 \mathrm{O}(g)$
(d) $\mathrm{O}(g)+\mathrm{N}_{2}(g) \longrightarrow \mathrm{NO}(g)+\mathrm{N}(g)$
(e) All of the above

James Irizarry

Numerade Educator

Problem 25

(a) What is the difference between chlorofluorocarbons and hydrofluorocarbons?
(b) Why are hydrofluorocarbons potentially less harmful to the ozone layer than CFCs?

Kevin Chimex

Numerade Educator

Problem 26

Draw the Lewis structure for the chlorofluorocarbon CFC-11, $\mathrm{CFCl}_{3}$. What chemical characteristics of this substance allow it to effectively deplete stratospheric ozone?

James Irizarry

Numerade Educator

Problem 27

The average bond enthalpies of the $\mathrm{C}-\mathrm{C}$ and $\mathrm{C}-\mathrm{H}$ bonds are $348 \mathrm{~kJ} / \mathrm{mol}$ and $413 \mathrm{~kJ} / \mathrm{mol}$, respectively. (a) What is the maximum wavelength that a photon can possess and still have sufficient energy to break the $\mathrm{C}-\mathrm{H}$ and $\mathrm{C}-\mathrm{C}$ bonds, respectively? (b) Given the fact that $\mathrm{O}_{2}, \mathrm{~N}_{2},$ and $\mathrm{O}$ in the upper atmosphere absorb most of the light with wavelengths shorter than $240 \mathrm{nm}$, would you expect the photodissociation of $\mathrm{C}-\mathrm{C}$ and $\mathrm{C}-\mathrm{H}$ bonds to be significant in the lower atmosphere?

Crystal Wang

Numerade Educator

Problem 28

(a) When chlorine atoms react with atmospheric ozone, what are the products of the reaction?
(b) Based on average bond enthalpies, would you expect a photon capable of dissociating a $\mathrm{C}-\mathrm{Cl}$ bond to have sufficient energy to dissociate a $\mathrm{C}-\mathrm{Br}$ bond? $(\mathbf{c})$ Would you expect the substance $\mathrm{CFBr}_{3}$ to accelerate depletion of the ozone layer?

Crystal Wang

Numerade Educator

Problem 29

Nitrogen oxides like $\mathrm{NO}_{2}$ and $\mathrm{NO}$ are a significant source of acid rain. For each of these molecules write an equation that shows how an acid is formed from the reaction with water.

Kevin Chimex

Numerade Educator

Problem 30

Why is rainwater naturally acidic, even in the absence of polluting gases such as $\mathrm{SO}_{2}$ ?

James Irizarry

Numerade Educator

Problem 31

(a) It has been reported, that acid rain with a pH of 3.5 could corrode mild steel. Write a chemical equation that describes the attack of acid rain on an iron (Fe) material.
(b) If the iron material were covered with a surface layer of copper, would this help to stop the effects of acid rain? Explain.

Crystal Wang

Numerade Educator

Problem 32

Copper exposed to air and water may be oxidized. The green oxidized product is referred to as "patina".
(a) Write a balanced chemical equation to show the reaction of copper to copper (II) ions with oxygen and protons from acid rain.
(b) Would you expect some kind of "patina" on a silver surface? Explain.

Crystal Wang

Numerade Educator

Problem 33

Alcohol-based fuels for automobiles lead to the production of formaldehyde $\left(\mathrm{CH}_{2} \mathrm{O}\right)$ in exhaust gases. Formaldehyde undergoes photodissociation, which contributes to photochemical smog:
$$
\mathrm{CH}_{2} \mathrm{O}+h \nu \longrightarrow \mathrm{CHO}+\mathrm{H}
$$
The maximum wavelength of light that can cause this reaction is $335 \mathrm{nm} .(\mathbf{a})$ In what part of the electromagnetic spectrum is light with this wavelength found? (b) What is the maximum strength of a bond, in $\mathrm{kJ} / \mathrm{mol}$, that can be broken by absorption of a photon of 335 -nm light?
(c) Compare your answer from part (b) to the appropriate value from Table 8.3 . What do you conclude about $\mathrm{C}-\mathrm{H}$ bond energy in formaldehyde? (d) Write out the formaldehyde photodissociation reaction, showing Lewis-dot structures.

Crystal Wang

Numerade Educator

Problem 34

An important reaction in the formation of photochemical smog is the photodissociation of $\mathrm{NO}_{2}$ :
$$
\mathrm{NO}_{2}+h \nu \longrightarrow \mathrm{NO}(g)+\mathrm{O}(g)
$$
The maximum wavelength of light that can cause this reaction is $420 \mathrm{nm} .$ (a) In what part of the electromagnetic spectrum is light with this wavelength found?
(b) What is the maximum strength of a bond, in $\mathrm{kJ} / \mathrm{mol}$, that can be broken by absorption of a photon of 420 -nm light? $?$
(c) Write out the photodissociation reaction showing Lewis-dot structures.

James Irizarry

Numerade Educator

Problem 35

Consider the Earth's energy balance shown in Figure 18.12 . (a) How many different sources transfer energy to the atmosphere? Which makes the largest contribution? What is the total amount of energy transferred into the atmosphere in $\mathrm{W} / \mathrm{m}^{2} ?(\mathbf{b})$ To maintain a balance the atmosphere must lose an equal amount of energy by emitting radiation, either into space or back toward the surface. What fraction is radiated back to the surface?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 36

The atmosphere of Mars is $96 \% \mathrm{CO}_{2}$, with a pressure of approximately $0.6 \mathrm{kPa}$ at the surface. Based on measurements taken over a period of several years by the Rover Environmental Monitoring Station (REMS), the average daytime temperature at the REMS location on Mars is $-5.7^{\circ} \mathrm{C},$ while the average nighttime temperature is $-79^{\circ} \mathrm{C}$. This daily variation in temperature is much larger than what we experience on Earth. What factor plays the largest role in this wide temperature variation, the composition or the density of the atmosphere?

Crystal Wang

Numerade Educator

Problem 37

What is the molarity of $\mathrm{Na}^{+}$ in a solution of $\mathrm{NaCl}$ whose salinity is 25.0 if the solution has a density of $1.04 \mathrm{~g} / \mathrm{mL}$ ?

Crystal Wang

Numerade Educator

Problem 38

Sulfur is present in seawater to the extent of $0.09 \%$ by mass. Assuming that the sulfur is present as sulfate, $\mathrm{SO}_{4}^{2-}$ calculate the corresponding molar concentration of $\mathrm{SO}_{4}^{2-}$ in seawater.

Crystal Wang

Numerade Educator

Problem 39

The enthalpy of evaporation of water is $40.67 \mathrm{~kJ} / \mathrm{mol}$. Sunlight striking Earth's surface supplies $168 \mathrm{~W}$ per square meter $(1 \mathrm{~W}=1 \mathrm{watt}=1 \mathrm{~J} / \mathrm{s}) .(\mathbf{a})$ Assuming that evaporation of water is due only to energy input from the Sun, calculate how many grams of water could be evaporated from a 1.00 square meter patch of ocean over a 12 -h day. (b) The specific heat capacity of liquid water is $4.184 \mathrm{~J} / \mathrm{g}^{\circ} \mathrm{C}$. If the initial surface temperature of a 1.00 square meter patch of ocean is $26^{\circ} \mathrm{C}$, what is its final temperature after being in sunlight for $12 \mathrm{~h}$, assuming no phase changes and assuming that sunlight penetrates uniformly to depth of $10.0 \mathrm{~cm} ?$

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 40

The enthalpy of fusion of water is $6.01 \mathrm{~kJ} / \mathrm{mol}$. Sunlight striking Earth's surface supplies $168 \mathrm{~W}$ per square meter $(1 \mathrm{~W}=1 \mathrm{watt}=1 \mathrm{~J} / \mathrm{s}) .($ a) Assuming that melting of ice is due only to energy input from the Sun, calculate how many grams of ice could be melted from a 1.00 square meter patch of ice over a $12-\mathrm{h}$ day. $(\mathbf{b})$ The specific heat capacity of ice is $2.032 \mathrm{~J} / \mathrm{g}^{\circ} \mathrm{C}$. If the initial temperature of a 1.00 square meter patch of ice is $-5.0^{\circ} \mathrm{C},$ what is its final temperature after being in sunlight for $12 \mathrm{~h}$, assuming no phase changes and assuming that sunlight penetrates uniformly to a depth of $1.00 \mathrm{~cm} ?$

James Irizarry

Numerade Educator

Problem 41

A first-stage recovery of magnesium from seawater is precipitation of $\mathrm{Mg}(\mathrm{OH})_{2}$ with $\mathrm{CaO};$
$$
\mathrm{Mg}^{2+}(a q)+\mathrm{CaO}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Mg}(\mathrm{OH})_{2}(s)+\mathrm{Ca}^{2+}(a q)
$$
What mass of $\mathrm{CaO}$, in grams, is needed to precipitate $1000 \mathrm{~kg}$ of $\mathrm{Mg}(\mathrm{OH})_{2} ?$

Crystal Wang

Numerade Educator

Problem 42

Platinum is found in seawater at very low levels, about 0.23 ppt (parts per trillion) by mass. How much platinum can be found in the entire ocean $\left(1.3 \times 10^{21} \mathrm{~L}\right)$ ? Assume the density of seawater is $1.03 \mathrm{~g} / \mathrm{mL}$. Estimate the price of the following amount of platinum: $\$ 1,600$ per troy ounce.

Crystal Wang

Numerade Educator

Problem 43

Although there are many ions in seawater, the overall charges of the dissolved cations and anions must maintain charge neutrality. Consider only the six most abundant ions in seawater, as listed in Table $18.5\left(\mathrm{Cl}^{-}, \mathrm{Na}^{+},\right.$ $\mathrm{SO}_{4}^{2-}, \mathrm{Mg}^{2+}, \mathrm{Ca}^{2+},$ and $\left.\mathrm{K}^{+}\right),$ calculate the total charge in Coulombs of the cations in $1.0 \mathrm{~L}$ of seawater. Calculate the total charge in Coulombs of the anions in $1.0 \mathrm{~L}$ of seawater. To how many significant figures are the two numbers equal?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 44

The Ogallala aquifer described in the Closer Look box in Section 18.3, provides $82 \%$ of the drinking water for the people who live in the region, although more than $75 \%$ of the water that is pumped from it is for irrigation. Irrigation withdrawals are approximately 18 billion gallons per day. (a) Assuming that $2 \%$ of the rainfall that falls on an area of $600,000 \mathrm{~km}^{2}$ recharges the aquifer, what average annual rainfall would be required to replace the water removed for irrigation? (b) What process or processes accounts for the presence of arsenic in well water?

James Irizarry

Numerade Educator

Problem 45

Suppose that one wishes to use reverse osmosis to reduce the salt content of brackish water containing $0.265 \mathrm{M}$ total salt concentration to a value of $0.015 \mathrm{M},$ thus rendering it usable for human consumption. What is the minimum pressure that needs to be applied in the permeators (Figure 18.20 ) to achieve this goal, assuming that the operation occurs at $15^{\circ} \mathrm{C} ?$ (Hint: Refer to Section 13.5.)

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 46

Assume that a portable reverse-osmosis apparatus operates on seawater, whose concentrations of constituent ions are listed in Table $18.5,$ and that the desalinated water output has an effective molarity of about $0.02 \mathrm{M}$. What minimum pressure must be applied by hand pumping at $297 \mathrm{~K}$ to cause reverse osmosis to occur? (Hint: Refer to Section 13.5.)

James Irizarry

Numerade Educator

Problem 47

List the common products formed when an organic material containing the elements carbon, hydrogen, oxygen, sulfur, and nitrogen decomposes (a) under aerobic conditions, (b) under anaerobic conditions.

Kevin Chimex

Numerade Educator

Problem 48

(a) Explain why the concentration of dissolved oxygen in freshwater is an important indicator of the quality of the water. (b) Find graphical data in the text that show variations of gas solubility with temperature, and estimate to two significant figures the percent solubility of $\mathrm{O}_{2}$ in water at $30^{\circ} \mathrm{C}$ as compared with $20^{\circ} \mathrm{C}$. How do these data relate to the quality of natural waters?

James Irizarry

Numerade Educator

Problem 49

Sodium stearate $\left(\mathrm{C}_{18} \mathrm{H}_{35} \mathrm{O}_{2} \mathrm{Na}\right)$ is the most common soap. Assume that the stearate anion undergoes aerobic decomposition in the following manner:
$$
\begin{aligned}
\mathrm{C}_{18} \mathrm{H}_{35} \mathrm{O}_{2}^{-}(a q)+26 \mathrm{O}_{2}(a q) & \longrightarrow \\
& 17 \mathrm{CO}_{2}(a q)+17 \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{HCO}_{3}^{-}(a q)
\end{aligned}
$$
What is the total mass of $\mathrm{O}_{2}$ required to biodegrade $3.0 \mathrm{~g}$ of this substance?

David Collins

Numerade Educator

Problem 50

Sewage causes removal of oxygen from the fresh water into which the sewage is discharged. For a town with a population of 100,000 people, this effluent causes a daily oxygen depletion of 50.0 g per person. How many liters of water at $8 \mathrm{ppm} \mathrm{O}_{2}$ are $50 \%$ depleted of oxygen in a day by the population of this town?

Crystal Wang

Numerade Educator

Problem 51

Hydrogen phosphate $\left(\mathrm{HPO}_{4}^{2-}\right)$ can be removed in water treatment by the addition of slaked lime, $\mathrm{Ca}(\mathrm{OH})_{2} .$ Write a balanced chemical equation for the reaction (using ions as reactant), in which $\mathrm{Ca}_{5}(\mathrm{OH})\left(\mathrm{PO}_{4}\right)_{3}$ forms as a precipitate.

Crystal Wang

Numerade Educator

Problem 52

In the lime soda process once used in large scale municipal water softening, calcium hydroxide prepared from lime and sodium carbonate are added to precipitate $\mathrm{Ca}^{2+}$ as $\mathrm{CaCO}_{3}(s)$ and $\mathrm{Mg}^{2+}$ as $\mathrm{Mg}(\mathrm{OH})_{2}(s);$
$$
\begin{aligned}
\mathrm{Ca}^{2+}(a q)+\mathrm{CO}_{3}^{2-}(a q) & \longrightarrow \mathrm{CaCO}_{3}(s) \\
\mathrm{Mg}^{2+}(a q)+2 \mathrm{OH}^{-}(a q) & \longrightarrow \mathrm{Mg}(\mathrm{OH})_{2}(s)
\end{aligned}
$$
How many moles of $\mathrm{Ca}(\mathrm{OH})_{2}$ and $\mathrm{Na}_{2} \mathrm{CO}_{3}$ should be added to soften (remove the $\mathrm{Ca}^{2+}$ and $\mathrm{Mg}^{2+}$ ) 1000 L of water in which
$$
\begin{array}{l}
{\left[\mathrm{Ca}^{2+}\right]=3.5 \times 10^{-4} \mathrm{M}} \\
{\left[\mathrm{Mg}^{2+}\right]=7.5 \times 10^{-4} \mathrm{M}}
\end{array}
$$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 53

(a) What are trihalomethanes (THMs)? (b) Draw the Lewis structures of two example THMs.

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 54

(a) Suppose that tests of a municipal water system reveal the presence of bromate ion, $\mathrm{BrO}_{3}^{-}$. What are the likely origins of this ion? (b) Is bromate ion an oxidizing or reducing agent?

James Irizarry

Numerade Educator

Problem 55

One of the principles of green chemistry is that it is better to use as few steps as possible in making new chemicals. In what ways does following this rule advance the goals of green chemistry? How does this principle relate to energy efficiency?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 56

Discuss how catalysts can make processes more energy efficient.

James Irizarry

Numerade Educator

Problem 57

A reaction for converting ketones to lactones, called the Baeyer-Villiger reaction,
is used in the manufacture of plastics and pharmaceuticals. 3-Chloroperbenzoic acid is shock-sensitive, however, and prone to explode. Also, 3 -chlorobenzoic acid is a waste product. An alternative process being developed uses hydrogen peroxide and a catalyst consisting of tin deposited within a solid support. The catalyst is readily recovered from the reaction mixture. (a) What would you expect to be the other product of oxidation of the ketone to lactone by hydrogen peroxide? (b) What principles of green chemistry are addressed by use of the proposed process?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 58

The hydrogenation reaction shown here was performed with an iridium catalyst, both in supercritical $\mathrm{CO}_{2}\left(\mathrm{scCO}_{2}\right)$ and in the chlorinated solvent $\mathrm{CH}_{2} \mathrm{Cl}_{2}$. The kinetic data for the reaction in both solvents are plotted in the graph. In what respects is the use of $\operatorname{scC} \mathrm{O}_{2}$ a good example of a green chemical reaction?

James Irizarry

Numerade Educator

Problem 59

In the following three instances, which choice is greener in each situation? Explain. (a) Petroleum as a raw material or vegetable oil as a raw material. (b) Toluene as a solvent or water as a solvent. (c) Catalyzed reaction at $600 \mathrm{~K}$ or uncatalyzed reaction at $800 \mathrm{~K}$.

Crystal Wang

Numerade Educator

Problem 60

In the following three instances, which choice is greener in a chemical process? Explain. (a) A reaction that can be run at $350 \mathrm{~K}$ for $12 \mathrm{~h}$ without a catalyst or one that can be run at $300 \mathrm{~K}$ for $1 \mathrm{~h}$ with a reusable catalyst. (b) A reagent for the reaction that can be obtained from corn husks or one that is obtained from petroleum. (c) A process that produces no by-products or one in which the by-products are recycled for another process.

James Irizarry

Numerade Educator

Problem 61

A friend of yours has seen each of the following items i newspaper articles and would like an explanation: $(\mathbf{a}$ acid rain, $(\mathbf{b})$ greenhouse gas, $(\mathbf{c})$ photochemical smog (d) ozone depletion. Give a brief explanation of each term an identify one or two of the chemicals associated with each.

Crystal Wang

Numerade Educator

Problem 62

Suppose that on another planet the atmosphere consists of $10 \% \mathrm{Kr}, 40 \% \mathrm{CH}_{4},$ and $50 \% \mathrm{O}_{2} .$ What is the average molar mass at the surface? What is the average molar mass at an altitude at which all the $\mathrm{O}_{2}$ is photodissociated?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 63

If an average $\mathrm{O}_{3}$, molecule "lives" only $100-200$ seconds in the stratosphere before undergoing dissociation, how can $\mathrm{O}_{3}$ offer any protection from ultraviolet radiation?

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 64

Show how Equations 18.7 and 18.9 can be added to give Equation 18.10

James Irizarry

Numerade Educator

Problem 65

What properties of CFCs make them ideal for various commercial applications but also make them a long-term problem in the stratosphere?

Kevin Chimex

Numerade Educator

Problem 66

Halons are fluorocarbons that contain bromine, such as $\mathrm{CBrF}_{3}$. They are used extensively as foaming agents for fighting fires. Like CFCs, halons are very unreactive and ultimately can diffuse into the stratosphere.
(a) Based on the data in Table 8.3 , would you expect photodissociation of $\mathrm{Br}$ atoms to occur in the stratosphere?
(b) Propose a mechanism by which the presence of halons in the stratosphere could lead to the depletion of stratospheric ozone.

James Irizarry

Numerade Educator

Problem 67

(a) What is the difference between a CFC and an HFC?
(b) It is estimated that the lifetime for HFCs in the stratosphere is $2-7$ years. Why is this number significant?
(c)Why have HFCs been used to replace CFCs?
(d) What is the major disadvantage of HFCs as replacements for CFCs?

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 68

Explain, using Le Châtelier's principle, why the equilibrium constant for the formation of $\mathrm{NO}$ from $\mathrm{N}_{2}$ and $\mathrm{O}_{2}$ increases with increasing temperature, whereas the equilibrium constant for the formation of $\mathrm{NO}_{2}$ from $\mathrm{NO}$ and $\mathrm{O}_{2}$ decreases with increasing temperature.

Shahina -

Numerade Educator

Problem 69

Liquefied petroleum gas (LPG) consists primarily of propane, $\mathrm{C}_{3} \mathrm{H}_{8}(l)$ or butane $\mathrm{C}_{4} \mathrm{H}_{10}(l)$
(a) Write a balanced chemical equation for the complete combustion of propane to produce $\mathrm{CO}_{2}(g)$ as the only carbon-containing product.
(b) Write a balanced chemical equation for the incomplete combustion of propane to produce $\mathrm{CO}(g)$ as the only carbon-containing product.
(c) At $25^{\circ} \mathrm{C}$ and
$101.3 \mathrm{kPa}$ pressure, what is the minimum quantity of dry air needed to combust $10.0 \mathrm{~mL}$ of $\mathrm{C}_{3} \mathrm{H}_{8}(l)$ completely to $\mathrm{CO}_{2}(g)$ ? The density of the LPG is $0.50 \mathrm{~g} / \mathrm{mL}$.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 70

It was estimated that the eruption of the Mount Pinatubo volcano resulted in the injection of 20 million metric tons of $\mathrm{SO}_{2}$ into the atmosphere. Most of this $\mathrm{SO}_{2}$ underwent oxidation to $\mathrm{SO}_{3},$ which reacts with atmospheric water to form an aerosol. (a) Write chemical equations for the processes leading to formation of the aerosol. (b) The aerosols caused a $0.5-0.6^{\circ} \mathrm{C}$ drop in surface temperature in the northern hemisphere. What is the mechanism by which this occurs? (c) The sulfate aerosols, as they are called, also cause loss of ozone from the stratosphere. How might this occur?

Crystal Wang

Numerade Educator

Problem 71

One of the possible consequences of climate change is an increase in the temperature of ocean water. The oceans serve as a "sink" for $\mathrm{CO}_{2}$ by dissolving large amounts of it.
(a) The figure below shows the solubility of $\mathrm{CO}_{2}$ in water as a function of temperature. Does $\mathrm{CO}_{2}$ behave more or less similarly to other gases in this respect?
(b) What are the implications of this figure for the problem of climate change?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 72

The rate of solar energy striking Earth averages 168 watts per square meter. The rate of energy radiated from Earth's surface averages 390 watts per square meter. Comparing these numbers, one might expect that the planet would cool quickly, yet it does not. Why not?

James Irizarry

Numerade Educator

Problem 73

In 2008 , the global average electricity consumption per head was $3.0 \mathrm{MWh}$. The solar power striking Earth every day averages 168 watts per square meter. Considering that present technology for solar energy conversion is about $10 \%$ efficient, from how many square meters of land must sunlight be collected in order to provide this power?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 74

Write balanced chemical equations for each of the following reactions: (a) The carbon dioxide molecule undergoes photodissociation in the upper atmosphere. (b) The carbon dioxide molecule undergoes photoionization in the upper atmosphere. (c) Carbon monoxide undergoes oxidation by ozone in the stratosphere. (d) Carbon dioxide dissolves in water to form hydrogen carbonate.

Crystal Wang

Numerade Educator

Problem 75

(a) When sufficient $\mathrm{Na}_{2} \mathrm{CO}_{3}$ is added to a solution containing $\mathrm{Mg}^{2+}, \mathrm{Mg}(\mathrm{OH})_{2}$ will precipitate. Explain by writing balanced equations of the reactions. (b) Will $\mathrm{Mg}(\mathrm{OH})_{2}$ precipitate when $2.0 \mathrm{~g}$ of $\mathrm{Na}_{2} \mathrm{CO}_{3}$ is added to $1.00 \mathrm{~L}$ of a solution containing 25 ppm of $\mathrm{Mg}^{2+}$ ?

Crystal Wang

Numerade Educator

Problem 76

The CDC (Centers for Disease Control and Prevention) published a reference blood lead level (BLL), which is based on the BLL distribution among children. It is currently $5 \mu \mathrm{p} / \mathrm{dL} .$ (a) What is the molarity of an aqueous solution with this concentration? (b) Express this concentration in ppb.

Crystal Wang

Numerade Educator

Problem 77

As of the writing of this text, EPA standards limit atmospheric ozone levels in urban environments to 84 ppb. How many moles of ozone would there be in the air above Los Angeles County (area about 10,000 square kilometers; consider a height of $100 \mathrm{~m}$ above the ground) if ozone was at this concentration?

Crystal Wang

Numerade Educator

Problem 78

The estimated average concentration of $\mathrm{NO}_{2}$ in air in the United States in 2015 was 0.010 ppm. (a) Calculate the partial pressure of the $\mathrm{NO}_{2}$ in a sample of this air when the atmospheric pressure is $101 \mathrm{kPa} .(\mathbf{b})$ How many molecules of $\mathrm{NO}_{2}$ are present under these conditions at $25^{\circ} \mathrm{C}$ in a room that measures $10 \mathrm{~m} \times 8 \mathrm{~m} \times 2.50 \mathrm{~m} ?$

Crystal Wang

Numerade Educator

Problem 79

A 500 megawatt electrical power plant typically burned 1,430,000 metric tons of coal in a year. (a) Assuming that the coal was $80 \%$ carbon and $3 \%$ sulfur and that combustion was complete, calculate the number of tons of carbon dioxide and sulfur dioxide produced by the plant during the year. (b) If $50 \%$ of the $\mathrm{SO}_{2}$ could be removed by reaction with powdered $\mathrm{CaO}$ to form $\mathrm{CaSO}_{3}$, how many tons of $\mathrm{CaSO}_{3}$ would be produced?

Crystal Wang

Numerade Educator

Problem 80

Figure 14.4 shows the visible spectra of iodine $\left(\mathrm{I}_{2}\right)$ solutions at different concentrations $(1 \mathrm{mg} / \mathrm{L}-100 \mathrm{mg} / \mathrm{L})$. The absorption maximum is at $450 \mathrm{nm}$.
(a) What color corresponds to a wavelength of $450 \mathrm{nm} ?$
(b) Calculate the extinction coefficient $\varepsilon$ of iodine in this solution at $450 \mathrm{nm}$. Assume a common spectrometer path length of $b=1.0 \mathrm{~cm}$

Crystal Wang

Numerade Educator

Problem 81

Common lab spectrometers can detect absorbance down to 0.0002 with good reliability. Consider a dissolved harmful organic substance with a molar mass of $120.5 \mathrm{~g} / \mathrm{mol}$, which can be detected in this spectrometer. It shows an extinction coefficient of $\varepsilon=1.43 \times 10^{3} \mathrm{M}^{-1} \mathrm{~cm}^{-1}$ at 320
$\mathrm{nm}$, its absorption maximum (A Closer Look, p. 620). (a) Calculate the minimum concentration of the organic substance detectable by this spectrometer (path length $1 \mathrm{~cm}$ ).
(b) Convert the minimum observable molarity to ppb.

Crystal Wang

Numerade Educator

Problem 82

The concentration of $\mathrm{H}_{2} \mathrm{O}$ in the stratosphere is about 5 ppm. It undergoes photodissociation according to:
$$
\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{H}(g)+\mathrm{OH}(g)
$$
(a) Write out the Lewis-dot structures for both products and reactant.
(b) Using Table 8.3 , calculate the wavelength required to cause this dissociation.
(c) The hydroxyl radical, OH, can react with ozone, giving the following reactions:
$$
\begin{aligned}
\mathrm{OH}(g)+\mathrm{O}_{3}(g) & \longrightarrow \mathrm{HO}_{2}(g)+\mathrm{O}_{2}(g) \\
\mathrm{HO}_{2}(g)+\mathrm{O}(g) & \longrightarrow \mathrm{OH}(g)+\mathrm{O}_{2}(g)
\end{aligned}
$$
What overall reaction results from these two elementary reactions? What is the catalyst in the overall reaction? Explain.

Crystal Wang

Numerade Educator

Problem 83

Bioremediation is the process by which bacteria repair their environment in response, for example, to an oil spill. The efficiency of bacteria for "eating" hydrocarbons depends on the amount of oxygen in the system, $\mathrm{pH}$, temperature, and many other factors. In a certain oil spill, hydrocarbons from the oil disappeared with a first-order rate constant of $2 \times 10^{-6} \mathrm{~s}^{-1}$. At that rate, how many days would it take for the hydrocarbons to decrease to $10 \%$ of their initial value?

Kim Trang Nguyen

Kim Trang Nguyen

Numerade Educator

Problem 84

The standard enthalpies of formation of $\mathrm{ClO}$ and $\mathrm{ClO}_{2}$ are 101 and $102 \mathrm{~kJ} / \mathrm{mol}$, respectively. Using these data and the thermodynamic data in Appendix C, calculate the overall enthalpy change for each step in the following catalytic cycle:
$$
\begin{array}{l}
\mathrm{ClO}(g)+\mathrm{O}_{3}(g) \longrightarrow \mathrm{ClO}_{2}(g)+\mathrm{O}_{2}(g) \\
\mathrm{ClO}_{2}(g)+\mathrm{O}(g) \longrightarrow \mathrm{ClO}(g)+\mathrm{O}_{2}(g)
\end{array}
$$
What is the enthalpy change for the overall reaction that results from these two steps?

James Irizarry

Numerade Educator

Problem 85

The main reason that distillation is a costly method for purifying water is the high energy required to heat and vaporize water. (a) Using the density, specific heat, and heat of vaporization of water from Appendix B, calculate the amount of energy required to vaporize $1.00 \mathrm{~L}$ of water beginning with water at $25^{\circ} \mathrm{C}$. (b) If the energy is provided by electricity costing $\$ 0.085 / \mathrm{kWh},$ calculate its cost. $(\mathbf{c})$ If distilled water sells in a grocery store for $\$ 0.49$ per $L,$ what percentage of the sales price is represented by the cost of the energy?

Crystal Wang

Numerade Educator

Problem 86

A reaction that contributes to the depletion of ozone in the stratosphere is the direct reaction of oxygen atoms with ozone:
$$
\mathrm{O}(g)+\mathrm{O}_{3}(g) \longrightarrow 2 \mathrm{O}_{2}(g)
$$
At $298 \mathrm{~K}$ the rate constant for this reaction is $4.8 \times 10^{5}$ $M^{-1} \mathrm{~s}^{-1}$. (a) Based on the units of the rate constant, write the likely rate law for this reaction. (b) Would you expect this reaction to occur via a single elementary process? Explain why or why not. (c) Use $\Delta H_{f}^{\circ}$ values from Appendix $\mathrm{C}$ to estimate the enthalpy change for this reaction. Would this reaction raise or lower the temperature of the stratosphere?

James Irizarry

Numerade Educator

Problem 87

The following data were collected for the decomposition of $\mathrm{O}_{3} \mathrm{by}\left(\mathrm{O}_{3}+\mathrm{H} \longrightarrow \mathrm{O}_{2}+\mathrm{OH}\right)$ at very low concentrations:
$$
\begin{array}{llll}
\hline \text { Trial } & {\left[\mathrm{O}_{3}\right](M)} & {[\mathrm{H}](M)} & \text { Initial Rate }(M / s) \\
\hline 1 & 3.25 \times 10^{-33} & 2.25 \times 10^{-26} & 8.10 \times 10^{-15} \\
2 & 6.50 \times 10^{-33} & 4.50 \times 10^{-26} & 3.25 \times 10^{-14} \\
3 & 6.48 \times 10^{-33} & 2.23 \times 10^{-26} & 1.62 \times 10^{-14} \\
\hline
\end{array}
$$
(a) Write the rate law for the reaction.
(b) Calculate the rate constant.

Nicole Smina

Numerade Educator

Problem 88

The degradation of $\mathrm{CF}_{3} \mathrm{CH}_{2} \mathrm{~F}$ (an HFC) by OH radicals in the troposphere is first order in each reactant and has a rate constant of $k=2.1 \times 10^{8} \mathrm{M}^{-1} \mathrm{~s}^{-1}$ at $10^{\circ} \mathrm{C}$. If the tropospheric concentrations of $\mathrm{OH}$ and $\mathrm{CF}_{3} \mathrm{CH}_{2} \mathrm{~F}$ are $1.0 \times 10^{12}$ and $7.5 \times 10^{14}$ molecules $/ \mathrm{m}^{3}$, respectively, what is the rate of reaction at this temperature in $M /$ s?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 89

The Henry's law constant for $\mathrm{CO}_{2}$ in water at $25^{\circ} \mathrm{C}$ is $3.4 \times 10^{-4} \mathrm{~mol} / \mathrm{m}^{3}-\mathrm{Pa}(\mathbf{a})$ What is the solubility of $\mathrm{CO}_{2}$ in water at this temperature if the solution is in contact with air at normal atmospheric pressure? (b) Assume that all of this $\mathrm{CO}_{2}$ is in the form of $\mathrm{H}_{2} \mathrm{CO}_{3}$ produced by the reaction between $\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}:$
$$
\mathrm{CO}_{2}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{H}_{2} \mathrm{CO}_{3}(a q)
$$
What is the pH of this solution?

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 90

The precipitation of $\mathrm{Al}(\mathrm{OH})_{3}\left(K_{s p}=1.3 \times 10^{-33}\right)$ is sometimes used to purify water. (a) Estimate the pH at which precipitation of $\mathrm{Al}(\mathrm{OH})_{3}$ will begin if $5.0 \mathrm{~kg}$ of $\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}$ is added to 10,000 L of water. (b) Approximately how many pounds of CaO must be added to the water to achieve this $\mathrm{pH}$ ?

Crystal Wang

Numerade Educator

Problem 91

The valuable polymer polyurethane is made by a condensation reaction of alcohols (ROH) with compounds that contain an isocyanate group (RNCO). Two reactions that can generate a urethane monomer are shown here:
(a) Which process, i or ii, is greener? Explain.
(b) What are the hybridization and geometry of the carbon atoms in each C-containing compound in each reaction?
(c) If you wanted to promote the formation of the isocyanate intermediate in each reaction, what could you do, using Le Châtelier's principle?

Crystal Wang

Numerade Educator

Problem 92

The $\mathrm{pH}$ of a particular raindrop is 5.6. (a) Assuming the major species in the raindrop are $\mathrm{H}_{2} \mathrm{CO}_{3}(a q), \mathrm{HCO}_{3}^{-}(a q),$ and $\mathrm{CO}_{3}^{2-}(a q),$ calculate the concentrations of these species in the raindrop, assuming the total carbonate concentration is $1.0 \times 10^{-5} \mathrm{M}$. The appropriate $K_{a}$ values are given in Table 16.3. (b) What experiments could you do to test the hypothesis that the rain also contains sulfur-containing species that contribute to its pH? Assume you have a large sample of rain to test.

James Irizarry

Numerade Educator