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Copyright © by The McGraw-Hill Companies, Inc.All rights reserved. Permission is granted to reproduce the material contained hereinon the condition that such material be reproduced only for classroom use; be providedto students, teachers, and families without charge; and be used solely in conjunctionwith the Chemistry: Matter and Change program. Any other reproduction, for use orsale, is prohibited without prior written permission of the publisher.

Send all inquiries to:Glencoe/McGraw-Hill8787 Orion PlaceColumbus, OH 43240-4027

ISBN 0-07-824533-8Printed in the United States of America.1 2 3 4 5 6 7 8 9 10 045 09 08 07 06 05 04 03 02 01

A Glencoe Program

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Challenge Problems Chemistry: Matter and Change iii

Chapter 1 Production of Chlorofluorocarbons, 1950–1992 . . . . . . . . . 1

Chapter 2 Population Trends in the United States . . . . . . . . . . . . . . . . 2

Chapter 3 Physical and Chemical Changes . . . . . . . . . . . . . . . . . . . . . 3

Chapter 4 Isotopes of an Element . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Chapter 5 Quantum Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Chapter 6 Döbereiner’s Triads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Chapter 7 Abundance of the Elements . . . . . . . . . . . . . . . . . . . . . . . . 7

Chapter 8 Comparing the Structures of Atoms and Ions . . . . . . . . . . . 8

Chapter 9 Exceptions to the Octet Rule . . . . . . . . . . . . . . . . . . . . . . . . 9

Chapter 10 Balancing Chemical Equations . . . . . . . . . . . . . . . . . . . . . 10

Chapter 11 Using Mole-Based Conversions . . . . . . . . . . . . . . . . . . . . 11

Chapter 12 Mole Relationships in Chemical Reactions . . . . . . . . . . . . 12

Chapter 13 Intermolecular Forces and Boiling Points . . . . . . . . . . . . . 13

Chapter 14 A Simple Mercury Barometer . . . . . . . . . . . . . . . . . . . . . . 14

Chapter 15 Vapor Pressure Lowering . . . . . . . . . . . . . . . . . . . . . . . . . 15

Chapter 16 Standard Heat of Formation . . . . . . . . . . . . . . . . . . . . . . . 16

Chapter 17 Determining Reaction Rates . . . . . . . . . . . . . . . . . . . . . . . 17

Chapter 18 Changing Equilibrium Concentrations in a Reaction . . . . . 18

Chapter 19 Swimming Pool Chemistry . . . . . . . . . . . . . . . . . . . . . . . . 19

Chapter 20 Balancing Oxidation–Reduction Equations . . . . . . . . . . . . 20

Chapter 21 Effect of Concentration on Cell Potential . . . . . . . . . . . . . 21

Chapter 22 Structural Isomers of Hexane . . . . . . . . . . . . . . . . . . . . . . 22

Chapter 23 Boiling Points of Organic Families . . . . . . . . . . . . . . . . . . 23

Chapter 24 The Chemistry of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Chapter 25 The Production of Plutonium-239 . . . . . . . . . . . . . . . . . . . 25

Chapter 26 The Phosphorus Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Answer Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . T27

CHALLENGE PROBLEMS

Contents

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iv Chemistry: Matter and Change Challenge Problems

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Challenge Problems Chemistry: Matter and Change • Chapter 1 1

Production ofChlorofluorocarbons, 1950–1992Production ofChlorofluorocarbons, 1950–1992

Chlorofluorocarbons (CFCs) were first produced in the laboratory in the late 1920s. They did not

become an important commercial product until sometime later. Eventually, CFCs grew in popularity untiltheir effect on the ozone layer was discovered in the1970s. The graph shows the combined amounts of twoimportant CFCs produced between 1950 and 1992.Answer the following questions about the graph.

CHALLENGE PROBLEMSCHAPTER 1

1. What was the approximate amount of CFCs produced in 1950? In 1960? In 1970?

2. In what year was the largest amount of CFCs produced? About how much was producedthat year?

3. During what two-year period did the production of CFCs decrease by the greatestamount? By about how much did their production decrease?

4. During what two-year period did the production of CFCs increase by the greatestamount? What was the approximate percent increase during this period?

5. How confident would you feel about predicting the production levels of CFCs during theodd numbered years 1961, 1971, and 1981? Explain.

6. Could the data in the graph be presented in the form of a circle graph? Explain.

Year

Am

ou

nt

of

CFC

s(b

illio

n k

ilog

ram

s)

050

100150200250300350400

1950 1960 1970 1980 1990

Use with Chapter 1,Section 1.1

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2 Chemistry: Matter and Change • Chapter 2 Challenge Problems

Population Trends in theUnited StatesPopulation Trends in theUnited States



1. By how much did the total U.S. population increase between 1990 and 2000? What wasthe percent increase during this period?

2. Calculate the total population for each of the five groups for 1990 and 2000.

3. Make a bar graph that compares the population for the five groups in 1990 and 2000. Inwhat ways is the bar graph better than the circle graphs? In what way is it less useful?

U.S. Population Distribution

(Percentages may not add up to 100% due to rounding.)

Caucasian71.4%Native American

0.70%

Asian American3.8%

Hispanic American11.8%

African American12.2%

Caucasian75.7%

Native American0.70%

Asian American2.8%

Hispanic American9.0%

African American11.8%

20001990

The population of the United States is becoming more diverse. The circle graphs below show thedistribution of the U.S. population among five ethnic groups in 1990 and 2000. The estimated

total U.S. population for those two years was 2.488 � 108 in 1990 and 2.754 � 108 in 2000.

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Physical and ChemicalChangesPhysical and ChemicalChanges

Physical and chemical changes occur all around us. One of the many places in which physical and chemical changes occur is the kitchen. For example, cooking spaghetti in a

pot of water on the stove involves such changes. For each of the changes described below, tell(a) whether the change that occurs is physical or chemical, and (b) how you made your choicebetween these two possibilities. If you are unable to decide whether the change is physical orchemical, tell what additional information you would need in order to make a decision.


1. As the water in the pot is heated, its temperature rises.

2. As more heat is added, the water begins to boil and steam is produced.

3. The heat used to cook is produced by burning natural gas in the stove burner.

4. The metal burner on which the pot rests while being heated becomes red as its temperature rises.

5. After the flame has been turned off, a small area on the burner has changed in color fromblack to gray.

6. A strand of spaghetti has fallen onto the burner, where it turns black and begins tosmoke.

7. When the spaghetti is cooked in the boiling water, it becomes soft.


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Isotopes of an ElementIsotopes of an Element

A mass spectrometer is a device for separatingatoms and molecules according to their

mass. A substance is first heated in a vacuum andthen ionized. The ions produced are acceleratedthrough a magnetic field that separates ions of dif-ferent masses. The graph below was producedwhen a certain element (element X) was analyzedin a mass spectrometer. Use the graph to answerthe questions below.



1. How many isotopes of element X exist?

2. What is the mass of the most abundant isotope?

3. What is the mass of the least abundant isotope?

4. What is the mass of the heaviest isotope?

5. What is the mass of the lightest isotope?

6. Estimate the percent abundance of each isotope shown on the graph.

7. Without performing any calculations, predict the approximate atomic mass for elementX. Explain the basis for your prediction.

8. Using the data given by the graph, calculate the weighted average atomic mass of element X. Identify the unknown element.

0

5

10

15

20

25

30

196194192190 198 200 202 204 206 208 210Atomic mass (amu)

Perc

ent

abu

nd

ance

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Quantum NumbersQuantum Numbers


The state of an electron in an atom can be completely described by four quantum numbers,designated as n, �, m�, and ms. The first, or principal, quantum number, n, indicates the

electron’s approximate distance from the nucleus. The second quantum number, �, describesthe shape of the electron’s orbit around the nucleus. The third quantum number, m�, describesthe orientation of the electron’s orbit compared to the plane of the atom. The fourth quantumnumber, ms, tells the direction of the electron’s spin (clockwise or counterclockwise).

The Schrödinger wave equation imposes certain mathematical restrictions on the quantumnumbers. They are as follows:

n can be any integer (whole number),

� can be any integer from 0 to n � 1,

m� can be any integer from �� to ��, and

ms can be � or �

As an example, consider electrons in the first energy level of an atom, that is, n � 1. Inthis case, � can have any integral value from 0 to (n � 1), or 0 to (1 � 1). In other words,� must be 0 for these electrons. Also, the only value that m� can have is 0. The electrons in

this energy level can have values of � or � for ms. These restrictions agree with the

observation that the first energy level can have only two electrons. Their quantum numbers

are 1, 0, 0, � and 1, 0, 0 � .

Use the rules given above to complete the table listing the quantum numbers for eachelectron in a boron atom. The correct quantum numbers for one electron in the atom is provided as an example.

1�2

1�2

1�2

1�2

1�2

1�2


Electron n � m� ms

1 1 0 0 �

2

3

4

5

1�2

Boron (B)

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Döbereiner’s TriadsDöbereiner’s Triads

One of the first somewhat successful attempts to arrange the elements in a systematic way was made by the German chemist Johann Wolfgang Döbereiner (1780–1849). In 1816,

Döbereiner noticed that the then accepted atomic mass of strontium (50) was midway betweenthe atomic masses of calcium (27.5) and barium (72.5). Note that the accepted atomic massesfor these elements today are very different from their accepted atomic masses at the timeDöbereiner made his observations. Döbereiner also observed that strontium, calcium, and bar-ium showed a gradual gradation in their properties, with the values of some of strontium’sproperties being about midway between the values of calcium and barium. Döbereiner eventu-ally found four other sets of three elements, which he called triads, that followed the same pat-tern. In each triad, the atomic mass of the middle element was about midway between theatomic masses of the other two elements. Unfortunately, because Döbereiner’s system did notturn out to be very useful, it was largely ignored.

Had Döbereiner actually discovered a way of identifying trends among the elements?Listed below are six three-element groups in which the elements in each group are consecutivemembers of the same group in the periodic table. The elements in each set show a gradation intheir properties. Values for the first and third element in each set are given. Determine the miss-ing value in each set by calculating the average of the two given values. Then, compare the val-ues you obtained with those given in the Handbook of Chemistry and Physics. Record theactual values below your calculated values. Is the value of the property of the middle elementin each set midway between the values of the other two elements in the set?



Element Melting Point (°C)

Fluorine �219.6

Chlorine Calculated:

Actual:

Bromine �7.2

Set 1

Element Atomic Mass

Lithium 6.941

Sodium Calculated:

Actual:

Potassium 39.098

Set 2

Element Boiling Point (°C)

Magnesium 1107

Calcium Calculated:

Actual:

Strontium 1384

Set 3


Krypton �153

Xenon Calculated:

Actual:

Radon �62

Set 4

Element Melting Point (°C)

Germanium 937

Tin Calculated:

Actual:

Lead 327

Set 5


Beryllium 1285

Magnesium Calculated:

Actual:

Calcium 851

Set 6

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Abundance of the ElementsAbundance of the Elements

The abundance of the elements differs significantly in various parts of the universe. The table below lists the abundance of some elements in various

parts of the universe. Use the table to answer the following questions.


1. What percent of all atoms in the universe are either hydrogen or helium? What percent ofall atoms in the solar system are either hydrogen or helium?

2. Explain the relatively high abundance of hydrogen and helium in the universe comparedto their relatively low abundance on Earth.

3. Only the top four most abundant elements on Earth and in Earth’s crust are shown in thetable. Name two additional elements you would expect to find among the top ten ele-ments both on Earth and in Earth’s crust. Explain your choices.

4. Name at least three elements in addition to those shown in the table that you wouldexpect to find in the list of the top ten elements in the human body. Explain your choices.


Abundance (Number of atoms per 1000 atoms)*

Element Universe Solar System Earth Earth’s Crust Human Body

Hydrogen 927 863 30 606

Helium 71.8 135

Oxygen 0.510 0.783 500 610 257

Nitrogen 0.153 0.0809 24

Carbon 0.0811 0.459 106

Silicon 0.0231 0.0269 140 210

Iron 0.0139 0.00320 170 19

* An element is not abundant in a region that is left blank.

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Comparing the Structures ofAtoms and IonsComparing the Structures ofAtoms and Ions

The chemical properties of an element depend primarily on its number of valence electrons in its atoms. The noble gas elements, for example, all have similar chemical properties

because the outermost energy levels of their atoms are completely filled. The chemical propertiesof ions also depend on the number of valence electrons. Any ion with a complete outermostenergy level will have chemical properties similar to those of the noble gas elements. The fluo-ride ion (F�), for example, has a total of ten electrons, eight of which fill its outermost energylevel. F� has chemical properties, therefore, similar to those of the noble gas neon.

Shown below are the Lewis electron dot structures for five elements: sulfur (S), chlorine (Cl),argon (Ar), potassium (K), and calcium (Ca). Answer the questions below about these structures.



1. Write the atomic number for each of the five elements shown above.

2. Write the electron configuration for each of the five elements.

3. Which of the above Lewis electron dot structures is the same as the Lewis electron dotstructure for the ion S2�? Explain your answer.

4. Which of the above Lewis electron dot structures is the same as that for the ion Cl�?Explain your answer.

5. Which of the above Lewis electron dot structures is like that for the ion K�? Explainyour answer.

6. Name an ion of calcium that has chemical properties similar to those of argon. Explainyour answer.

S Cl Ar K Ca

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Exceptions to the Octet RuleExceptions to the Octet Rule

The octet rule is an important guide to understanding how most compounds are formed. However, there are a number of cases in which the octet rule does not apply. Answer the

following questions about exceptions to the octet rule.


1. Draw the Lewis structure for the compound BeF2.

2. Does BeF2 obey the octet rule? Explain.

3. Draw the Lewis structure for the compound NO2.

4. Does NO2 obey the octet rule? Explain.

5. Draw the Lewis structure for the compound N2F2.

6. Does N2F2 obey the octet rule? Explain.

7. Draw the Lewis structure for the compound IF5.

8. Does IF5 obey the octet rule? Explain.


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Balancing ChemicalEquationsBalancing ChemicalEquations



Each chemical equation below contains at least one error. Identify the error or errors and then write the correct chemical equation for the reaction.

1. K(s) � 2H2O(l) 0 2KOH(aq) � H2(g)

2. MgCl2(aq) � H2SO4(aq) 0 Mg(SO4)2(aq) � 2HCl(aq)

3. AgNO3(aq) � H2S(aq) 0 Ag2S(aq) � HNO3(aq)

4. Sr(s) � F2(g) 0 Sr2F

5. 2NaHCO3(s) � 2HCl(aq) 0 2NaCl(s) � 2CO2(g)

6. 2LiOH(aq) � 2HBr(aq) 0 2LiBr(aq) � 2H2O

7. NH4OH(aq) � KOH(aq) 0 KOH(aq) � NH4OH(aq)

8. 2Ca(s) � Cl2(g) 0 2CaCl(aq)

9. H2SO4(aq) � 2Al(NO3)3(aq) 0 Al2(SO4)3(aq) � 2HNO3(aq)

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Using Mole-BasedConversionsUsing Mole-BasedConversions

The diagram shows three containers, each of which holds a certain mass of the substance indicated. Complete the table below for each of the three substances.


1. Compare and contrast the number of representative particles and the mass of UF6 withthe number of representative particles and mass of CCl3CF3. Explain any differences you observe.

2. UF6 is a gas used in the production of fuel for nuclear power plants. How many moles ofthe gas are in 100.0 g of UF6?

3. CCl3CF3 is a chlorofluorocarbon responsible for the destruction of the ozone layer inEarth’s atmosphere. How many molecules of the liquid are in 1.0 g of CCl3CF3?

4. Lead (Pb) is used to make a number of different alloys. What is the mass of lead presentin an alloy containing 0.15 mol of lead?

UF6 (g)

225.0 g

CCl3CF3 (l)

200.0 g

Pb (s)

250.0 g


Molar Mass Number of Number of Representative Substance Mass (g) (g/mol) Moles (mol) Particles

UF6(g)

CCl3CF3(l)

Pb(s)

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Mole Relationships inChemical ReactionsMole Relationships inChemical Reactions

The mole provides a convenient way of finding the amounts of the substances in a chemical reaction. The diagram below shows how this concept can be applied to the reaction

between carbon monoxide (CO) and oxygen (O2), shown in the following balanced equation.

2CO(g) � O2(g) 0 2CO2(g)

Use the equation and the diagram to answer the following questions.



1. What information is needed to make the types of conversions shown by double-arrow 1in the diagram?

2. What conversion factors would be needed to make the conversions represented by double-arrow 2 in the diagram for CO? By double-arrow 6 for CO2?

3. What information is needed to make the types of conversions represented by double-arrows 3 and 7 in the diagram?

4. What conversion factors would be needed to make the conversions represented by double-arrow 3 in the diagram for CO?

5. Why is it not possible to convert between the mass of a substance and the number of representative particles, as represented by double-arrow 4 of the diagram?

6. Why is it not possible to use the mass of one substance in a chemical reaction to find the massof a second substance in the reaction, as represented by double-arrow 5 in the diagram?

Moles ofCO

Grams ofCO

Moles ofCO2

Grams ofCO2

Particles ofCO

Particles ofCO2

1

5

2

3

46

7

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Intermolecular Forces andBoiling PointsIntermolecular Forces andBoiling Points


1. How do the boiling points of the group 4A hydrides change as the molecular masses ofthe hydrides change?

2. What are the molecular structure and polarity of the four group 4A hydrides?

3. Predict the strength of the forces between group 4A hydride molecules. Explain howthose forces affect the boiling points of group 4A hydrides.

4. How do the boiling points of the group 6A hydrides change as the molecular masses ofthe hydrides change?

5. What are the molecular structure and polarity of the four group 6A hydrides?

6. Use Table 9-4 in your textbook to determine the difference in electronegativities of thebonds in the four group 6A hydrides.

100

0

�100

H2O

H2S

CH4

SiH4

GeH4

SnH4

H2Se

H2Te

Group 6Ahydrides

Group 4Ahydrides

Molecular mass

Bo

ilin

g p

oin

t (°

C)

00 50 100 150


The boiling points of liquids depend partly on the mass of the particles of which they are made. The greater the mass of

the particles, the more energy is needed to convert a liquid to agas, and, thus, the higher the boiling point of the liquid. This pat-tern may not hold true, however, when there are significant forcesbetween the particles of a liquid. The graph plots boiling pointversus molecular mass for group 4A and group 6A hydrides. Ahydride is a binary compound containing hydrogen and one otherelement. Use the graph to answer the following questions.

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A Simple Mercury BarometerA Simple Mercury Barometer

In Figure 1, a simple mercury barometer is made by filling a long glass tube with mercury and then inverting the open end of the

tube into a bowl of mercury. Answer the following questions aboutthe simple mercury barometer shown here.



1. What occupies the space above the mercury column in thebarometer’s glass tube?

2. What prevents mercury from flowing out of the glass tube into the bowl of mercury?

3. When the barometer in Figure 1 is moved to a higher elevation, such as an altitude of5000 meters, the column of mercury changes as shown in Figure 2. Why is the mercurycolumn lower in Figure 2 than in Figure 1?

4. Suppose the barometer in Figure 1 was carried into an open mine 500 meters below sealevel. How would the height of the mercury column change? Explain why.

5. Suppose the liquid used to make the barometer was water instead of mercury. How wouldthis substitution affect the barometer? Explain.

6. Suppose a tiny crack formed at the top of the barometer’s glass tube. How would thisevent affect the column of mercury? Explain why.

Glass tube

Mercury column

Bowl of mercury

At sea level At 500 metersabove sea level

Figure 1 Figure 2

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Vapor Pressure LoweringVapor Pressure Lowering

You have learned that adding a nonvolatile solute to a solvent lowers the vapor pressure of that solvent. The amount by

which the vapor pressure is lowered can be calculated by means of a relationship discovered by the French chemist François MarieRaoult (1830–1901) in 1886. According to Raoult’s law, the vaporpressure of a solvent (P) is equal to the product of its vapor pressurewhen pure (P0) and its mole fraction (X) in the solution, or

P � P0X

The solution shown at the right was made by adding 75.0 g ofsucrose (C12H22O11) to 500.0 g of water at a temperature of 20°C.Answer the following questions about this solution.


1. Why do the sugar molecules in the solution lower the vapor pressure of the water?

2. What is the number of moles of sucrose in the solution?

3. What is the number of moles of water in the solution?

4. What is the mole fraction of water in the solution?

5. What is the vapor pressure of the solution if the vapor pressure of pure water at 20°C is17.54 mm Hg?

6. How much is the vapor pressure of the solution reduced from that of water by the addition of the sucrose?

Watermolecule

Solution

Sucrosemolecule


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Standard Heat of FormationStandard Heat of Formation

Hess’s law allows you to determine the standard heat of formation of a compound

when you know the heats of reactions that leadto the production of that compound. The firstdiagram on the right shows how Hess’s law canbe used to calculate the heat of formation ofCO2 by knowing the heats of reaction of twosteps leading to the production of CO2. Use thisdiagram to help you answer the questions belowabout the second diagram.



The equations below show how NO2 can be formed in two ways: directly from the elements or in two steps.

N2(g) � O2(g) 0 NO2(g) �H � 33 kJ/mol

or

N2(g) � O2(g) 0 NO(g) �H � 91 kJ/mol

NO(g) � O2(g) 0 NO2(g) �H � �58 kJ/mol

1. On the diagram at the right, draw arrowheadsto show the directions in which the three lineslabeled 1, 2, and 3 should point.

2. Write the correct reactants and/or products oneach of the lines labeled A, B, and C.

3. Write the correct enthalpy change next toeach number on the diagram.

1�2

1�2

1�2

1�2

CO(g) � O2(g)

�H � �110 kJ/mol

C(s) � O2(g)

�H � �393 kJ/mol

�H � �283 kJ/molEnth

alp

y

CO2(g)

12

NO2(g)

�H � �58 kJ/mol

NO(g) � 1/2 O2(g)

�H � 91 kJ/mol

Enth

alp

y

�H � 33 kJ/mol

1

2

3

A

B

C

1/2 N2(g) � O2(g)

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Determining Reaction RatesDetermining Reaction Rates

Dinitrogen pentoxide decomposes to produce nitrogen dioxide and oxygen as represented

by the following equation.

2N2O5(g) 0 4NO2(g) � O2(g)

The graph on the right represents the concen-tration of N2O5 remaining as the reaction proceedsover time. Answer the following questions aboutthe reaction.


1. What is the concentration of N2O5 at the beginning of the experiment? After 1 hour?After 2 hours? After 10 hours?

2. By how much does the concentration of N2O5 change during the first hour of the reaction? Calculate the percentage of change the concentration undergoes during the first hour of the reaction.

3. The instantaneous rate of reaction is defined as the change in concentration of reactantduring some specified time period, or instantaneous rate of reaction = [N2O5]/t. What isthe instantaneous rate of reaction for the decomposition of N2O5 for the time periodbetween the first and second hours of the reaction? Between the second and third hours?Between the sixth and seventh hours?

4. What is the instantaneous rate of reaction for the decomposition of N2O5 between the sec-ond and fourth hours of the reaction? Between the third and eighth hours of the reaction?

5. How long does it take for 0.10 mol of N2O5 to decompose during the tenth hour of the reaction?

6. What is the average rate of reaction for the decomposition of N2O5 overall?

Time (h)

Co

nce

ntr

atio

n (

mo

l/L)

0.2

0

0.4

0.6

0.8

1.0

1.2

1.4

1.6

10 2 3 4 5 6 7 8 9 10


87654321

10

0 2 3 4 5Time (sec)

Co

nce

ntr

atio

n (

mo

l/L)

6 7 8 9 10

SO2

SO3

SO3

O2O2

SO2

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Changing EquilibriumConcentrations in a Reaction

Reversible reactions eventually reach an equilibrium condition in which the concentrations of all reactants

and products are constant. Equilibrium can be disturbed,however, by the addition or removal of either a reactant orproduct. The graph on the right shows how the concentra-tions of the reactants and product of a reaction changewhen equilibrium is disturbed. Use the graph to answer thefollowing questions.



1. Write the equation for the reaction depicted in the graph.

2. Write the equilibrium constant expression for the reaction.

3. Explain the shapes of the curves for the three gases during the first 2 minutes of the reaction.

4. At approximately what time does the reaction reach equilibrium? How do you knowequilibrium has been reached?

5. What are the concentrations of the three gases at equilibrium?

6. Calculate the value of Keq for the reaction.

7. Describe the change made in the system 4 minutes into the reaction. Tell how you knowthe change was made.

8. At what time does the system return to equilibrium?

Changing EquilibriumConcentrations in a Reaction

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Swimming Pool ChemistrySwimming Pool Chemistry

The presence of disease-causing bacteria in swimming pools is a major health concern. Chlorine gas is added to the water in some large commercial swimming pools to kill

bacteria. However, in most home swimming pools, either solid calcium hypochlorite(Ca(OCl)2) or an aqueous solution of sodium hypochlorite (NaOCl) is used to treat thewater. Both compounds dissociate in water to form the weak acid hypochlorous acid(HOCl). Hypochlorous acid is a highly effective bactericide. By contrast, the hypochloriteion (OCl�) is not a very effective bactericide. Use the information above to answer the following questions about the acid-base reactions that take place in swimming pools.


1. Write an equation that shows the reaction between hypochlorous acid and water. Identifythe acid, base, conjugate acid, and conjugate base in this reaction.

2. Write an equation that shows the reaction that occurs when the hypochlorite ion (OCl�),in the form of calcium hypochlorite or sodium hypochlorite, is added to water. Name theacid, base, conjugate acid, and conjugate base in this reaction.

3. What effect does the addition of hypochlorite ion have on the pH of swimming pool water?

4. The effectiveness of hypochlorite ion as a bactericide depends on pH. How does high pHaffect the equilibrium reaction described in question 2? What effect would high pH haveon the bacteria?

5. In the presence of sunlight, hypochlorite ion decomposes to form chloride ion and oxygen gas. Write an equation for this reaction and tell how it affects the safety of pool water.


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Balancing Oxidation–Reduction EquationsBalancing Oxidation–Reduction Equations

Scientists have developed a number of methods for protecting metals from oxidation. One such method involves the use of a

sacrificial metal. A sacrificial metal is a metal that is more easily oxidized than the metal it is designed to protect. Galvanized iron, forexample, consists of a piece of iron metal covered with a thin layer of zinc. When galvanized iron is exposed to oxygen, it is the zinc,rather than the iron, that is oxidized.

Water heaters often contain a metal rod that is made by coating a heavy steel wire with magnesium or aluminum. In this case, themagnesium or aluminum is the sacrificial metal, protecting the ironcasing of the heater from corrosion.

The diagram shows a portion of a water heater containing a sacrificial rod. Answer the following questions about the diagram.



1. In the absence of a sacrificial metal, oxygen dissolved in water may react with the ironcasing of the heater. One product formed is iron(II) hydroxide (Fe(OH)2). Which elementis oxidized and which is reduced in this reaction?

2. Balance the oxidation–reduction equation for this reaction:Fe(s) � O2(aq) � H2O 0 Fe(OH)2(aq)

3. Write the two half-reactions for this example of corrosion.

4. Suppose the sacrificial rod in the diagram above is coated with aluminum metal. Writethe balanced equation for the reaction of aluminum with oxygen dissolved in the water.(Hint: The product formed is aluminum hydroxide (Al(OH)3).

5. Write the two half-reactions for this example of corrosion.

6. Suppose that some iron in the casing of the water heater is oxidized, as shown in theequation of question 2 above. The sacrificial metal (aluminum, in this case) immediatelyrestores the Fe2� ions to iron atoms. Write two half-reactions that represent this situation.

Ironcasing

Steel wire

Sacrificialmetal

Water

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Effect of Concentration onCell PotentialEffect of Concentration onCell Potential

In a voltaic cell where all ions have a concentration of 1M, the cell potential is equal to the standard potential. For cells in which ion concentrations are greater or

less than 1M, as shown below, an adjustment must be made to calculate cell potential.That adjustment is expressed by the Nernst equation:

Ecell � E0cell � �log

In this equation, n is the number of moles of electrons transferred in the reaction,and x and y are the coefficients of the product and reactant ions, respectively, in thebalanced half-cell reactions for the cell.

[product ion]x��[reactant ion]y

0.0592�n


1. Write the two half-reactions and the overall cell reaction for the cell shown above.

2. Use Table 21-1 in your textbook to determine the standard potential of this cell.

3. Write the Nernst equation for the cell.

4. Calculate the cell potential for the ion concentrations shown in the cell.

Voltmeter

Ag Cu

Cu2�

1.0 � 10�3MAg�

1.0 � 10�2M


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Structural Isomers of HexaneStructural Isomers of Hexane

The structural formula of an organic compound can sometimes be written in a variety of ways, but sometimes structural formulas that appear similar can

represent different compounds. The structural formulas below are ten ways of representing compounds having the molecular formula C6H14.


Use with Chapter 22,Sections 22.1 and 22.3

1. In the spaces provided, write the correct name for each of the structural formulas, labeleda–j, above.

a. e. i.

b. f. j.

c. g.

d. h.

2. How many different compounds are represented by the structural formulas above? Whatare their names?

CH3

CH2 CH2 CH2 CH2 CH3

a.

CH3

CH3

CH CH2 CH2 CH3

b.

CH3

CH3

CH3 CH CH CH3

c.

CH3

CH3

CH3 C CH2 CH3

d.

CH3

CH CH2

CH2

CH3

CH3e.

CH3 CH CH CH3

CH3 CH3

f.

CH2

CH2 CH3

CH CH3

CH3

g.

CH3

CH2

CH3 CH CH2

CH3

h.

CH2

CH3

CH2

CH2 CH2

CH3i.

CH3

CH2 CH CH2

CH3 CH3j.

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Boiling Points of OrganicFamiliesBoiling Points of OrganicFamilies

The most important factor determining the boiling point of a substance is its atomic or molecular mass. In general,

the larger the atomic or molecular mass of the substance, themore energy is needed to convert the substance from the liquidphase to the gaseous phase. As an example, the boiling pointof ethane (molecular mass � 30; boiling point � �89°C) ismuch higher than the boiling point of methane (molecularmass � 16; boiling point � �161°C).

Intermolecular forces between the particles of a liquid alsocan affect the liquid’s boiling point. The graph shows trends inthe boiling points of four organic families: alkanes, alcohols,aldehydes, and ethers. Use the graph and your knowledge ofintermolecular forces to answer the following questions.


1. For any one family, what is the relationship between molecular mass and boiling point?

2. For compounds of similar molecular mass, which family of the four shown in the graphhas the lowest boiling points? Which family has the highest boiling points?

3. Find and list the boiling points for ethanol (molecular mass � 46) and dimethyl ether(molecular mass � 46) on the graph. Why would you expect these two compounds tohave relatively similar boiling points?

4. Find the aldehyde with a molecular mass of about 58. Name that aldehyde and write itschemical formula.

5. Can this aldehyde form hydrogen bonds? Can other aldehydes form hydrogen bonds?Explain.

30 40 50 60Molecular mass

� alkane� alcohol

Bo

ilin

g p

oin

t (°

C)

70 80

�50

0

50

100

� aldehyde� ether


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The Chemistry of LifeThe Chemistry of Life

Proteins are synthesized when RNA molecules translate the DNA language of nitrogen bases

into the protein language of amino acids using agenetic code. The genetic code is found in RNA mole-cules called messenger RNA (mRNA), which are syn-thesized from DNA molecules. The genetic codeconsists of a sequence of three nitrogen bases in themRNA, called a codon. Most codons code for specificamino acids. A few codons code for a stop in the syn-thesis of proteins. The table shows the mRNA codonsthat make up the genetic code. To use the table, readthe three nitrogen bases in sequence. The first base isshown along the left side of the table. The second baseis shown along the top of the table. The third base isshown along the right side of the table. For example,the sequence CAU codes for the amino acid histidine(His). The table gives abbreviations for the aminoacids. Answer the following questions about thegenetic code.



1. What amino acid is represented by each of the following codons?

a. CUG b. UCA

2. Write the sequence of amino acids for which the following mRNA sequence codes.

-C-A-U-C-A-C-C-G-G-U-C-U-U-U-U-C-U-U-

3. Errors sometimes occur when mRNA molecules are synthesized from DNA molecules.Nitrogen bases may be omitted, an extra nitrogen base may be added, or a nitrogen basemay be changed during synthesis. The two mRNA sequences shown below are examplesof such errors. In each case, tell how the mRNA sequence shown differs from the correctmRNA sequence given in question 2.

a. -C-A-U-C-A-C-C-G-G-U-U-C-U-U-U-U-C-U-U-

b. -C-A-U-U-A-C-C-G-G-U-C-U-U-U-U-C-U-U-

4. Write the amino acid sequence for each of the mRNA sequences shown in question 3.

a.

b.

UUU UCU UAU UGU UUUC UCC UAC UGC CUUA UCA UAA UGA AUUG UCG UAG UGG GCUU CCU CAU CGU UCUC CCC CAC CGC CCUA CCA CAA CGA ACUG CCG CAG CGG GAUU ACU AAU AGU UAUC ACC AAC AGC CAUA ACA AAA AGA AAUG ACG AAG AGG GGUU GCU GAU GGU UGUC GCC GAC GGC CGUA GCA GAA GGA AGUG GCG GAG GGG G

Second base

Firs

t b

ase Th

ird b

ase

}} Phe

Leu

Ile

Met

Leu

Val

Pro

Ser

Ala

Thr

}

}}

}}

}}

His

Gln

Tyr

StopStop

Asn

Lys

Asp

Glu

}

}}

Arg

Gly

Cys

StopTrp

Ser

Arg

U

C

A

G

U C A G

The Genetic Code

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The Production ofPlutonium-239The Production ofPlutonium-239

When nuclear fission was first discovered, only two isotopes, uranium-233 and uranium-235, were

known of being capable of undergoing this nuclear change.Scientists later discovered a third isotope, plutonium-239,also could undergo nuclear fission. Plutonium-239 does notoccur in nature but can be made synthetically in nuclearreactors and particle accelerators.

The diagram shows the process by which plutonium-239is made in nuclear reactors. Answer the questions about thediagram.


1. Identify the isotope whose nucleus is labeled A in the

diagram.

2. Name the type of nuclear reaction that occurs when a

neutron strikes nucleus A.

3. Identify the isotope whose nucleus is labeled B.

4. Besides fragmented nuclei, what else is produced when a neutron strikes nucleus A?

5. Identify the isotope whose nucleus is labeled C.

6. Write the nuclear equation for the reaction that occurs when a neutron strikes nucleus C.Identify the product D formed in the reaction.

7. Write the nuclear equation for the decay of nucleus D. Identify isotope E formed in thereaction.

8. Write a balanced nuclear equation for the decay of nucleus E. Identify isotope F formedin the reaction.

9. Name the type of nuclear reaction that occurs when a neutron strikes nucleus F.

10. Write the nuclear equation for the reaction that occurs when a neutron strikes nucleus F.Identify isotope G formed in the reaction.

0–1

0–1

00

10n

10n

10n

10n

45p75n

48p77n

92p143n92p

143n

92p146nSource

ofneutrons

B

A

C

D

E

G

F


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The Phosphorus CycleThe Phosphorus Cycle

Phosphorus is an important element both in organisms and in the lithosphere. In organisms, phosphorus occurs in DNA and RNA molecules, cell membranes, bones

and teeth, and in the energy–storage compound adenosine triphosphate (ATP). In the litho-sphere, phosphorus occurs primarily in the form of phosphates, as a major constituent ofmany rocks and minerals. Phosphate rock is mined to produce many commercial products,such as fertilizers and detergents. When these products are used, phosphates are returned tothe lithosphere and hydrosphere. Thus, phosphorus—like carbon and nitrogen—cycles in theenvironment. Use the diagram of the phosphorus cycle to answer the questions below.



1. By what methods does phosphorus get into soil?

2. By what method do plants obtain the phosphorus they need?

3. By what method do animals obtain the phosphorus they need?

4. In what way is the phosphorus cycle different from the carbon and nitrogen cycles youstudied in the textbook?

5. The phosphorus cycle has both short-term and long-term parts. Use different colored pencils to show each part on the diagram.

Phosphate rocks

Phosphaterocks

Geological uplift

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