from the six-part elements of chemistry...

Acids, Bases, and Saltsfrom the six-part

Elements of Chemistry Series

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Table of Contents

The purchase of this program entitles the user to the right to reproduce orduplicate, in whole or in part, this teacher’s guide and the blackline mas-ter handouts that accompany it for the purpose of teaching in conjunctionwith this program, Acids, Bases, and Salts. This right is restricted onlyfor use with this program. Any reproduction or duplication in whole or inpart of this guide and the blackline master handouts for any purpose otherthan for use with this program is prohibited.

This video is closed captioned.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Links to Curriculum Standards . . . . . . . . . . . . .1

Student Objectives . . . . . . . . . . . . . . . . . . . . . .1

Summary of the Program . . . . . . . . . . . . . . . . .2

Pre-Test and Post-Test . . . . . . . . . . . . . . . . . . .3

Teacher Preparation . . . . . . . . . . . . . . . . . . . . .3

Student Preparation . . . . . . . . . . . . . . . . . . . . . .4

Description of Blackline Masters . . . . . . . . . . .5

Answer Key . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Discussion Questions . . . . . . . . . . . . . . . . . . . .8

Follow-Up Activities . . . . . . . . . . . . . . . . . . . .10

References . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Script of Narration . . . . . . . . . . . . . . . . . . . . . .12

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1

Acids, Bases, and Saltsfrom the six-part Elements of Chemistry Series

Grades 9 to 12Viewing Time: 20 minutes

INTRODUCTIONAcids, Bases, and Salts, is part of the Elements of ChemistrySeries, a six-part series of programs to help students understandthe fundamental concepts of chemistry. The attractive imagesand engaging narration of the program have been designed byeducators and filmmakers to help students understand thesometimes complicated and obscure explanations of this impor-tant branch of science.

Of all the many different classes of compounds that are funda-mental to the functioning of our world, there are two: acids andbases. They are essential for life and lie at the heart of manydifferent processes in nature.

This program describes the properties of acids and bases andexplains how a slight change in the chemical composition of anacid or a base will fundamentally change the substance. Theprogram provides a comprehensive introduction to this area ofchemistry appropriate for high school students.

LINKS TO CURRICULUM STANDARDSThe Elements of Chemistry Series is based on the "NationalScience Educational Standards" for "Physical Science," grades9-12, (Content Standard B).

STUDENT OBJECTIVESAfter viewing the program and participating in the various fol-low-up activities, students should be able to:

• Explain that acids and bases are essential for life and are at theheart of a host of natural processes.

• Name a number of common acids and bases and describe theirgeneral characteristics.

2

• Describe the process of neutralization when acids react withbases to produce water and a salt.

• Provide a description of Arrhenius's definition of acids andbases and show how it explains the neutralization process.

• Describe the Brønsted and Lowry definition and explain whyit advances our understanding of the chemical processes ofacids and bases.

• Explain the chemical reasons why some substances are strongacids and others weak acids, and why some substances arestrong bases and others weak bases.

• Explain the chemistry of conjugate acid-base pairs.

• Describe the pH scale and explain what it measures.

• Explain why the pH scale is an important tool that is used ina wide variety of fields such as agriculture, environmental stud-ies, and biology.

SUMMARY OF THE PROGRAMAcids and bases are at the heart of a host of processes in nature.When dissolved in water, acids taste sour, or tart, while baseshave a bitter taste. Acids react with metals, while bases do not.

The first chemical explanation of acids and bases was given bySvante Arrhenius. He found that when dissolved in water, acidsrelease hydrogen ions, H

+, and bases generate hydroxide ions,

OH¯. He was able to show that when acids and bases are com-bined, they neutralize each other, and produce water and a salt.The general equation is: Acid + Base Salt + Water.

In a refinement of this theory, Brønsted and Lowry definedacids as any substance that can donate a hydrogen ion, H

+, and

a base as any substance that can accept a hydrogen ion.Essentially, a base is the opposite of an acid. That is why theyare so closely linked.

3

Some acids are very strong and others relatively weak. A strongacid is one that readily transfers H

+ ions to water, while a weak

acid is one that does not readily transfer H+

ions to water. Theopposite is the case for bases. Strong bases readily accept H

+

ions and a weak base only partially accepts H+

ions.

The pH scale, or potential hydrogen scale, was developed totest the degree to which substances are acids or bases. Thisscale is a useful tool and is widely used in such areas as biolo-gy, environmental science, and agriculture.

PRE-TEST and POST-TESTBlackline Master #1, Pre-Test, is an assessment tool intendedto gauge student comprehension prior to viewing the program.Remind your students that these are key concepts upon whichthey should focus while watching the program.

Blackline Master #7, Post-Test, can be compared to the resultsof the Pre-Test to determine the changes in student comprehen-sion after participation in the activities and viewing the pro-gram.

TEACHER PREPARATIONBefore presenting this program to your students, we suggestthat you preview the program and review this guide and accom-panying Blackline Master activities in order to familiarize your-self with the content. Feel free to duplicate any of the BlacklineMasters and distribute them to your students.

As you review the materials presented in this guide, you mayfind it necessary to make some changes, additions, or deletionsto meet the specific needs of your class. We encourage you todo this. Only by tailoring this program to your class will yourstudents obtain the maximum instructional benefits afforded bythe materials.

We suggest that you first show the program in its entirety toyour students. This is an introduction to an important subject

4

of modern chemistry; and at this stage, it is helpful that studentsgain an overview of the concepts and material in the program.A number of lesson activities will grow out of the content of theprogram and, therefore, the presentation should be a commonexperience for all students.

After the introduction, the program is divided into chapters withthe following titles:

• Properties of Acids and Bases• The Arrhenius Definition of Acids and Bases• The Brønsted and Lowry Definition• Strong and Weak Acids and Bases• Conjugate Acid-Base Pairs• The pH Scale• The pH in the Chemistry of Nature

These chapters vary in length from three to five minutes. Afterthe students have seen the entire program, lessons could bedesigned around these different chapters. A chapter could beshown at the beginning of the class, and the balance of the classtime, and subsequent classes, could be spent examining the sub-ject matter in the program in greater depth.

STUDENT PREPARATIONIt is important that students work through the material andfamiliarize themselves with the vocabulary, concepts, and theo-ries that scientists use to understand this field.

If the students have a textbook that they are following, assignthe relevant reading before the lesson. As students workthrough the material, they will encounter a number of unfamil-iar words and concepts. Most of these words are highlighted inthe program. An additional list of words is provided in Black-line Masters #2a-c, Vocabulary Definitions and Activities.

The program concludes with a ten-question Video Quiz thatmay be used to gauge students' comprehension immediately

5

after the presentation of the program. Blackline Master #6,Video Quiz, is a printed copy of the questions, which may bereproduced and distributed to the students. The answers to thequestions appear in the answer key of this Teacher's Guide.

DESCRIPTION OF BLACKLINE MASTERSBlackline Master #1, Pre-Test, should be given to studentsbefore viewing the program. When these answers are comparedto the quiz results, it will help you gauge students' progress.

Blackline Master #2a, Vocabulary Definitions, will introducestudents to unfamiliar words and concepts used in this program.Blackline Master #2b: Use the Right Word, and BlacklineMaster #2c: Word Match, are activities designed to help rein-force key concepts and vocabulary.

Blackline Master #3, Connected/Not Connected, will helpstudents identify their knowledge of key vocabulary terms andthe context in which they are used.

Blackline Master #4, Crossword Puzzle, reinforces key con-cepts and vocabulary.

Blackline Master #5, Creative Writing Story Ideas, willallow students to think creatively while incorporating scientificprinciples and vocabulary covered in this program.

Blackline Master #6, Video Quiz, is a printed version of theVideo Quiz that appears at the end of the program.

Blackline Master # 7, Post-Test, may be used to evaluate stu-dent progress after completing this lesson.

6

ANSWER KEYBlackline Master #1, Pre-Test1. True 6. False2. False 7. True3. True 8. True4. True 9. False5. False 10. False

Blackline Master #2b, Use the Right Word1. acid 6. neutralization2. base 7. pH3. acid rain 8. positive4. electrolytes 9. H

+

5. litmus or indicator 10. OH¯

Blackline Master #2c, Word Matchacid- can donate a hydrogen atom

anion- negatively charged ion

base- can accept a hydrogen ion

cation- positively charged ion

electrolytes- good conductors of electricity

H+

ion- positive hydrogen ion

litmus paper- acids turn it red, bases turn it blue

proton- positively charged particle

strong base- solution with a pH between 10 and 14

weak acid- solution with a pH between 4 and 6

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Blackline Master #3, Connected/Not Connected1. acid base2. anion cation3. electron proton4. ion atom5. H

+hydrogen

6. strong weak7. water salt8. negative positive9. Brønsted Lowry

10. OH¯

H2O

Blackline Master #4, Crossword Puzzle

Blackline Master #6, Video Quiz1. True 6. hydrogen ions2. False 7. True3. neutralization 8. False4. False 9. True5. True 10. acid rain

1

2

3

4 5 6 7

8 9

10

11

12 13

14 15

B

N

CONJUGATE

S

U

NEGATIVE

T

L

R

E

A

ACID

L

T

ION

R

L

Z

POSITIVE

A

N

T

L

T

M

E

I

P

U

C

O

ARRHENIUS

T

N

O

+

R

T

O

H2O

L

N

YATOM

E

C C

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Blackline Master #7, Post-Test1. neutralization2. base3. anion4. electrolytes5. False. A neutral atom has the same number of protons and

electrons. An ion has more or less electrons than protons.6. False. Acid rain, or rainfall that has a pH level below 5.6, is

harmful to vegetation, aquatic life, and corrodes building mate-rials.

7. True8. False. A conjugate acid-base pair differs by one H

+ion.

9. False. A H+

ion has no electrons. It is a single proton.10. Bases have a bitter taste and feel slippery, like soapy water.Bases are electrolytes because they are good conductors ofwater.11. According to the Brønsted/Lowry definition, an acid is anysubstance that can donate a H

+ion, and a base is any substance

that can accept a H+ ion.

12. The pH scale is a measurement of the acidity and basicityof substances. Water has a pH of 7 and is in the middle of thescale. Acids have numbers less than 7 and bases have numbersgreater than 7. This scale is used in such varied fields as agri-culture and medicine and is often used to determine the acidityof rainwater.

DISCUSSION QUESTIONS1. How do strong acids burn your skin when you come into con-tact with them?A strong acid is one that readily transfers H

+ions to water. All

human tissue, including skin, has a high proportion of water.When a strong acid comes in contact with skin, virtually all ofthe H

+ions in the acid are transferred to the skin. The H

+ions

are highly reactive and can burn skin.

9

2. What steps should be taken when someone spills acid on hisor her skin?Pour water on the skin immediately. The water will wash awaythe acid, but also the H

+ions in the acid will readily transfer to

the water rather than the skin and the burning will be mini-mized.

3. Why are bases not as dangerous as acids?This is a misconception. Weak acids and weak bases are notdangerous, but both strong acids and strong bases can both beharmful to human tissue. Lime is a very strong base and thereare small amounts of lime in concrete and mortar. Constructionworkers should be careful not to get it on their skin. If there isan accident, the concrete or mortar should be washed away asquickly as possible.

4. How can farmers control the pH levels in their soils to max-imize yields?Farmers should test the soils in their fields for pH levels andother nutrients on a regular basis. There are a number of agri-cultural institutes and private companies that provide this serv-ice. The pH levels can be adjusted by adding different types offertilizer to the soil.

5. Does an upset stomach have something to do with too muchacid in the stomach?Yes. We have strong acids in our stomachs that help to breakdown food in the digestion process. Sometimes too much acidbuilds up in the stomach, which irritates the walls of the stom-ach, giving discomfort. This is often called "acid indigestion."The usual remedy is to take an antacid pill or drink. The antacidis a base that neutralizes the acids in the stomach and restoresit to a normal range. That stops the irritation and the discom-fort should disappear.

10

FOLLOW-UP ACTIVITIESThe following activities and projects are designed to help stu-dents understand acids, bases, and salts.

1. Pour vinegar into a small bowl and put soapy water into asecond bowl. Feel and taste each of the solutions. Test each ofthe solutions with litmus, or indicator, paper. Write your find-ings in the form of a research report.

2. Explain why both acids and bases are electrolytes.

3. Draw diagrams of an H+

ion and an OH¯ ion. Use your draw-

ings to illustrate why H2O results when the two ions are mixedtogether.

4. Use the Brønsted and Lowry definition to explain how acidsand bases are neutralized when they are mixed together. Givesome examples.

5. Explain how water can be both an acid and a base.

6. Research the pH levels of three different commercial fertiliz-ers. What is the most appropriate fertilizer for roses, peonies,tomatoes, and potatoes? Write a report on your findings.

7. Interview the chief horticulturalist in your municipality or alarge local nursery. What fertilizer is recommended for plants inyour area? Do you think their recommendations are based ongood science or are they just guesswork?

8. Research the history of the pH scale and give some examplesof its usefulness.

9. Research the pH levels of the following substances: limejuice, liquid detergent, a solution of antacid, vitamin C, andwater.

11

10. Research the impact of acid rain on plants and fish. Writea report recommending some measures that can be taken tosolve this problem.

REFERENCESThere are many excellent books and websites dealing withacids, bases, and salts that are appropriate for students. The fol-lowing is a short list.

Books:LeMay, Eugene, Karen M. Robblie, Herbert Beall, DouglasBrower, Chemistry: Connections to Our Changing World,Englewood Cliffs, New Jersey, Prentice Hall, 1996.

McMurry, John, Mary E. Castellion, General, Organic andBiological Chemistry, Second Edition, Englewood Cliffs, NewJersey, Prentice Hall, 1996.

McMurry, John, Robert C. Fay, Chemistry, Englewood Cliffs,New Jersey, Prentice Hall, 1995.

Oxtoby, David W. and Norman N. Nachtrieb, Principles ofModern Chemistry, Fort Worth, Saunders College Publishing,1996.

Smoot, Robert C., Richard G. Smith, Jack Price, Chemistry,Glencoe, McGraw Hill, 1998.

Internet Sites:http://highschoolhub.org/hub/chemistry.cfm

http://dir.yagoo.com/Science/Chemistry/

http://dbhs.wvusd.k12.ca.us/ChemTeamIndex

http://www.visionlearing.com/library/science/chemistry-2CHE2.2-acid_base.htm

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www.sparknotes.com/chemistry/acidbases

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch11/acidbaseframe.html

http://scifun.chem.wisc.edu/HOMEEXPTS/ACIDBASE.html

http://www.chemistrycoach.com/acids.htm

SCRIPT OF NARRATIONOf all of the different classes of compounds that exist, there aretwo, acids and bases, that are fundamental to the functioning ofour world. They are essential for life, they are at the heart of ahost of processes in nature, and they are important in manyindustrial products and processes. We are going to examine theproperties of acids and bases and illustrate how these com-pounds influence our world.

PROPERTIES OF ACIDS AND BASESAcids! The very word evokes the image of dreadful burns andcorrosive liquids that eat away at almost everything, and yet,there are many different types of acids. Some, like ascorbicacid, better known as Vitamin C, are essential for life.

When they are dissolved in water, acids make solutions thattaste sour, or tart. Foods that contain acids include citrus fruits,cheese, vinegar, and sour milk. Soda pop is also a mild acid.Bases have a bitter taste. Soap and cleaning materials are basesand anyone who has accidentally put soap in his or her mouthcan attest to the bitter taste.

To the touch, acids feel like water, but eat an orange when youhave a sore in your mouth and you will find out that even mildacids can sting. Bases, on the other hand, feel slippery, likesoapy water. Both acids and bases are electrolytes, good con-ductors of electric current.

Acids react vigorously with metals such as zinc, iron, alu-minum, and magnesium. This is a piece of magnesium inhydrochloric acid. The reaction produces hydrogen gas. Bases,on the other hand, do not react with metals.

Chemists can use these, and other tests, to determine if solu-tions are acids or bases, but a much easier and more accuratetest is with pH indicator paper. This special paper reacts withboth acids and bases. A base turns indicator paper blue, and anacid turns it red. Chemists use indicator paper as a quick andinexpensive test of solutions.

THE ARRHENIUS DEFINITION OF ACIDS AND BASESThe 17th century English chemist, Robert Boyle, was the firstto study acids and bases in a systematic way. Boyle found thatthese two types of compounds counteract each other. Acidsreact with bases so that the properties of both are lost to formwater and a salt. This process is called neutralization.

Boyle's observations were an important advance, but he couldnot explain why these reactions were happening. It was notuntil the late 19th century that a Swedish chemist, SvanteArrhenius, made the first steps to unravel this mystery.

Arrhenius found that water often could dissolve both acids andbases by separating them into individual ions. For example,hydrochloric acid—HCl—separates in water. What has hap-pened in this reaction is that the original molecule, made up ofone atom of hydrogen and one atom of chlorine, dissociates inwater into its constituent H

+and Cl

¯ions. The hydrogen has

become a positively charged ion, or cation, while the chlorinehas become a negatively charged ion, or anion. Hydrogen hasonly one proton and one electron, so a positive hydrogen ion isone simple proton.

Arrhenius found a similar process works when bases are dis-solved in water, but rather than releasing a positive hydrogenion, it generates hydroxide ions, OH

¯. For example, when sodi-

13

um hydroxide, NaOH, is dissolved in water, this is the reaction.In water, the sodium hydroxide dissociates. The sodium, Na,becomes a positive ion because its electron has gone to hydrox-ide, OH

¯, which is a negative ion.

Arrhenius summarized his findings by defining acids as sub-stances that release hydrogen ions, H

+, when dissolved in water;

and bases are substances that generate hydroxide ions, OH¯,

when dissolved in water. This definition explained a number ofthings. It showed that acids have similar properties and baseshave similar properties. It solved the mystery as to why acidsand bases neutralize each other. When these two substances aremixed together, the H

+from the acid mixes with the OH

¯from

the base to produce H2O—water.

Arrhenius was also able to show that in the neutralizationprocess, when an acid and a base are combined, they producewater and a salt. The general equation is:

Acid + Base Water + Salt

For example, when hydrochloric acid is combined with sodiumhydroxide, a base, it produces water, and an ionic compoundcalled a salt. We think of salt as table salt that we put on foodbut there are many different salts, all of them ionic compounds.

THE BRØNSTED-LOWRY DEFINITIONArrhenius's explanation of acids and bases was an importantadvance, but there were problems with it. His definitions couldnot explain why a number of products, like baking soda, actedlike a base but did not have any hydroxide ions. His explana-tion also is limited to the reactions of acids and bases in water.

In 1923, a Danish chemist, Johannes Brønsted, and an Englishchemist, Thomas Lowry, published independent but similarfindings that refined Arrhenius's work. Their theories havecome to be called "The Brønsted and Lowry Definition ofAcids and Bases."

14

The definition that they used for acids was similar to Arrhenius.An acid, they said, was any substance that can donate a hydro-gen ion, or proton. But their definition of a base is very differ-ent. They define a base as any substance that can accept a pro-ton. Essentially, a base is the opposite of an acid.

The Brønsted/Lowry definition expands the number of sub-stances that can be acids and bases, and shows the close rela-tionship between them. It explains why substances that do notcontain OH

¯ can act like bases.

Under the Brønsted/Lowry definition, both acids and bases arerelated to the concentration of hydrogen ions, or protons pres-ent. Acids increase the concentration by donating protons,while bases decrease the concentration by accepting them.Therefore, the acidity, or basicity, of something can be meas-ured by its proton concentration.

STRONG AND WEAK ACIDS AND BASESSome acids, like vinegar, are relatively mild. If you spill a lit-tle on your hand when you put it on a salad, there is not muchto worry about. But others, like hydrochloric acid, HCl, arevery strong and can be extremely dangerous. As the two solu-tions sit in beakers, they look virtually the same, but why is oneso much stronger than the other?

A strong acid is one that readily transfers H+

ions to water. Themore complete the transfer of hydrogen ions, the stronger theacid. For example, when hydrochloric acid is mixed with water,nearly all of the HCl molecules transfer the H

+ions to water to

yield ions of H3O+.

By contrast, a weak acid, like vinegar, does not dissociate, ortransfer, H

+ions as readily in water. Only 0.4% of the acid mol-

ecules in vinegar transfer their H+

ions. That 99.6% does notdissociate. That is why vinegar is such a weak acid and whyhydrochloric acid is so strong.

15

Substances that have the strongest attraction for H+

ions arestrong bases. Lime that is used to make the mortar that holdsbricks together is a very strong base. The oxide ion O2

-that is

found in the lime strongly attracts the H+

ions. Other base com-pounds only partially react with water. These are weak bases.

Water has the tendency to equalize the strengths of all strongacids and strong bases. When strong acids are dissolved inwater, they lose their H

+ion to the water and H3O

+is formed,

which is a weaker acid than the original. In the same way, whenstrong bases are dissolved in water, they gain H

+ions from the

water, and thus, become weaker. This is known as the levelingeffect.

CONJUGATE ACID-BASE PAIRSAlthough acids and bases react very differently, they are con-nected in similar chemical reactions. According to the Brøn-sted/Lowry definition, an acid is a proton donor and a base is aproton acceptor. When an acid donates a proton, the remainingpart can now accept a proton, so it is now a base. This is calleda conjugate acid-base pair and they differ by only one proton.

This chart shows several conjugate acid-base pairs. There is aninverse relationship between the strength of the conjugate baseand its conjugate acid: the stronger the acid, the weaker its con-jugate base, and the stronger the base, the weaker its conjugateacid.

This relationship means a solution can sometimes be changedfrom acidic to basic and back again, a characteristic importantfor all living things.

THE pH SCALEWater can act as either an acid or a base. When a water mole-cule gives up a H

+ion to become an OH

¯ion, it is an acid. And

if it accepts a H+

ion to become a H3O+

ion, it is a base. Thisprocess occurs naturally even in the purest of water, but only infractions of amounts. With pure water, the amount of H3O

+ions

16

is 10-7 mole per liter, or one ten-millionth of a mole per liter.Although these are incredibly small amounts, they are measur-able and determine whether a solution is an acid or a base.

In 1909, a Danish biochemist, Søren Sørensen, proposed a wayof measuring the concentration of H3O+ ions in solutions, and inthe process, measure their acidity and basicity. It is known asthe potential hydrogen or, pH scale. This is the pH scale. Somecommon solutions and products are listed above, the pH scaleis in the center, and the measure of H3O

+is shown below.

The pH scale is a measurement of the amount of H3O+

ions inthe solution. Water is 10

-7mole. The others range from 10

-1to

10-14

. The pH number comes from the exponent. Notice thatwater with a pH of 7 is right in the middle of the scale. All ofthe solutions lower than 7 are acids, and all those higher than 7are bases. Lemon juice, for example, is an acid. It has a meas-ure of about 10

-2.5H3O

+ions in the solution. On the pH scale,

lemon juice measures 2.5. Bleach, on the other hand, is a strongbase and measures 12.5 on the pH scale. It has about 10

-12.5H3O

+

ions in the solution.

At first glance, the pH scale seems complicated, but it is reallyan ingenious measurement of the acidity and basicity of com-pounds and a very useful chemistry tool.

THE pH IN THE CHEMISTRY OF NATUREThe acidity and basicity of compounds is at the heart of chem-istry, and many people from farmers to medical personnel mustknow about the impact of pH levels if they are going to beeffective in their work. Many substances act as acids or basesand they react with other substances all of the time.

Plants generally prefer neutral soil with pH ranging from 6 to 8,but each plant species is a little different. Roses, for example,prefer a slightly acidic soil of between pH 5.8 and 6.2. Peonies,on the other hand, may not flower if the soil is too acidic.Gardeners interested in having the most vibrant colors and

17

blossoms in their gardens carefully monitor the pH of theirflowerbeds. Experienced farmers know the pH of their fields isvery important if they are to maximize yields, and they adjustpH by adding fertilizer.

Even rainfall is carefully monitored for its pH. Most rainwateris between 6 and 7 on the pH scale, but rain with a pH of below5.6 is called acid rain. Some rainfall has been measured as lowas pH 3.5. The cause of acid rain is coal-burning power plantsand the exhaust from automobiles. The burning of fossil fuelreleases sulfur dioxide and sulfur trioxide, which combineswith water vapor to produce acid.

Acid rain harms both living and non-living things. It can cor-rode metals, marble, and limestone. Plants can be seriouslydamaged by acid rain. It washes the nutrients out of the soil,damages the leaves and bark of trees, and harms the root sys-tems of plants. The acid in the rainfall also makes its way intorivers and lakes and kills fish and other aquatic life.

The balance of acids and bases in the bodies of animals is vitalfor their survival. The pH in different parts of a human bodyvaries considerably. Saliva is slightly acidic, while there arestrong acids in the stomach and intestine that play an importantrole in the digestion process.

The pH of blood is particularly sensitive. Human blood musthave a pH between the narrow range of 7.35 and 7.45.Anything outside this range can lead to serious health problemsor even death. Our bodies have a special method to keep the pHat a normal level. We maintain a mixture of acids and basescalled buffers in our bloodstream, which release or absorb H

+

ions to keep a normal pH.

Bases and acids are fundamental to life itself.

18

Name ____________

Directions: This will help you discover what you know about acids, bases, and salts before you beginthis lesson. Answer the following True or False.

1. Acids and bases are fundamental to the functioning of our world. T_______ F_______

2. Bases are rarer than acids. T_______ F_______

3. Chemists can use indicator paper, or litmus paper, to determine if a solution is an acid or a base. T_______ F_______

4. Acids and bases react with each other so that both are neutralized. T_______ F_______

5. Salts can produce acids and bases. T_______ F_______

6. A strong base has the same strength as a weak acid. T_______ F_______

7. Water can act as both an acid and a base. T_______ F_______

8. The potential hydrogen scale is known as the pH scale. T_______ F_______

9. Bases cannot be measured on the pH scale. T_______ F_______

10. The human body does not contain acids or bases. T_______ F_______

1

© 2003 Algonquin Educational Productions Published and Distributed by United LearningAll rights to print materials cleared for classroom duplication and distribution.

ACIDS, BASES, AND SALTS from the Elements of Chemistry SeriesPre-Test

2aName ____________


ACIDS, BASES, AND SALTS from the Elements of Chemistry SeriesVocabulary Definitions

acid - According to the Brønsted-Lowrydefinition, an acid is any substance thatcan donate a hydrogen ion.

acid rain - Rainfall that is acidic, below5.6 on the pH scale.

anion - Negatively charged ion.

Arrhenius, Svante (1859-1927) -Swedish chemist.

atom - The fundamental unit of matter inthe universe, made up of a nucleus ofprotons and neutrons and orbiting elec-trons.

atomic number - The number of an ele-ment determined by the number of pro-tons in its nucleus.

base - According to the Brønsted-Lowrydefinition, a base is any substance thatcan accept a hydrogen ion.

Boyle, Robert (1627-1691) - Englishchemist. Boyle is often called the fatherof modern chemistry.

Brønsted, Johannes (1879-1947) -Danish chemist.

cation - Positively charged ion.

chemical reaction - A change in thechemical composition of a substance.

conjugate acid-base pair - An acid anda base that differ by only one H

+ion.

compounds - When valence electrons ofelements are lost, gained, or sharedbetween different atoms to create sub-stances with unique chemical properties.

electrolytes - Substances that are goodconductors of electricity.

electrons - Negatively charged particlesthat orbit the nucleus of atoms.

element - An atom with a unique numberof protons.

hydrogen - Element with the atomicnumber 1. Hydrogen is the most com-mon element in the universe.

H+

ion - A positive hydrogen ion com-posed of one proton.

indicator paper - Paper that indicateswhether a substances is an acid or a base.Litmus paper is a common type of indi-cator paper.

ion - Atoms with more electrons thanprotons or less electrons than protons.

ionic bonds - Two or more ions heldtogether by the electrical attractionsbetween them.

litmus paper - A special type of paperthat can determine if a solution is an acidor a base. An acid turns litmus paper redand a base turns it blue.

Lowry, Thomas (1847-1936) - Englishchemist.

matter - Material that makes up objects.Matter cannot be created or destroyed.

molecules - When electrons are sharedbetween atoms. Molecules are covalentbonds.

negative ion - An ion that has more elec-trons than protons.

neutral atom - When an atom has anequal number of protons and electrons,its electrical charges are balanced and theatom has a neutral electrical charge.

neutral acid or base - A solution thathas a pH of 7 and is both an acid and abase. Pure water, H2O, has a pH of exact-ly 7.

neutralization - A process where acidsand bases react so that the properties ofboth are lost to form water and a salt.

OH¯

ion - A hydroxide ion composed ofan oxygen atom and a negative hydrogenion.

periodic table - The arrangements of ele-ments according to their atomic number.

pH scale - the potential hydrogen scale isa measurement of the concentration ofH3O

+ions in solutions to indicate whether

the solution is an acid or a base.

positive ion - An ion that has fewer elec-trons than protons.

proton - Positively charged part of thenucleus of atoms.

Sørensen, Søren (1868-1939) - Danishchemist.

strong acid - An acid with a pH ofbetween 0 and 4.

strong base - A base with a pH ofbetween 10 and 14.

weak acid - An acid with a pH ofbetween 4 and 6.

weak base - A base with a pH of between8 and 10.

The following words and terms used in the program may be unfamiliar to you. Try to listen for these terms whileviewing the program, pay close attention so you can later include them in your scientific descriptions, observa-tions, and creative writing assignment activities.

Name ____________

2b


Directions: Find the right word from the vocabulary list that completes the following sentences.

1. According to the Brønsted-Lowry definition, an ____________ is any substance that can donate a

hydrogen ion.

2. According to the Brønsted-Lowry definition, a ____________ is any substance that can accept a hydrogen ion.

3. Rainfall that is below 5.6 on the pH scale is called ____________ ____________.

4. Substances that are good conductors of electricity are called ____________.

5. A special type of paper that can determine if a solution is an acid or a base is called ____________ paper.

6. The process in which acids and bases react so that the properties of both are lost to form water and a salt is called ____________.

7. The scale that measures the concentration of H3O+

ions in solutions is called the ____________ scale.

8. An ion that has fewer electrons than protons is called a ____________ ion.

9. The symbol for a positive hydrogen ion is written ____________ ion.

10. The symbol for a hydroxide ion is written ____________ ion.

ACIDS, BASES, AND SALTS from the Elements of Chemistry SeriesUse the Right Word

2cName ____________


ACIDS, BASES, AND SALTS from the Elements of Chemistry SeriesWord Match

Directions: Connect the word with the proper definition.

acid positively charged ion

anion solution with a pH between 10 and 14

base solution with a pH between 4 and 6

cation acids turn it red, bases turn it blue

electrolytes positively charged particle

H+

ion negatively charged ion

litmus paper can accept a hydrogen ion

proton can donate a hydrogen atom

strong base positive hydrogen ion

weak acid good conductors of electricity

Name ____________

3


ACIDS, BASES, AND SALTS from the Elements of Chemistry SeriesConnected/Not Connected

Directions: Place the following words in the proper sentences.

acid cation ion protonanion electron Lowry saltatom H+ negative strongbase H2O OH¯ waterBrønsted hydrogen positive weak

1. An ____________ is connected to a ____________ because one type of substance can donate a hydrogen ion and the other type of substance can accept a hydrogen ion.

2. An ____________ is NOT connected to ____________ because one is a positively charged ion and the other is a negatively charged ion.

3. An ____________ is connected to a ____________ because both are particles of an atom.

4. An ____________ is NOT connected to neutral ____________ because one has an equal number of protons and electrons and the other has fewer or more electrons than protons.

5. An ____________ ion is connected to a ____________ atom because both have one proton.

6. A ____________ acid is NOT connected to a ____________ base because one has a pH between 0 and 4 and the other has a pH between 8 and 10.

7. ____________ is connected to ____________ because both are produced when an acid and a base are combined.

8. A ____________ ion is NOT connected to a ____________ ion because one of these ions has more electrons than protons and the other has fewer electrons than protons.

9. Johannes ____________ is connected to Thomas ____________ because both are credited with developing our modern understanding of acids and bases.

10. A ____________ ion is NOT connected to ____________ because the ion has one more electron than water.

Name ____________

4


ACIDS, BASES, AND SALTS from the Elements of Chemistry SeriesCrossword Puzzle

1

2

3

4 5 6 7

8 9

10

11

12 13

14 15

C CAcross

3. Positively charged particle7. Single proton.9. Negatively charged particle.

10. Acid turns this paper red, bases turn it blue.12. Can accept a hydrogen ion.13. Good conductor of electricity.14. When properties of acids and bases are lost.

Down

1. Water2. Swedish chemist, Svante _______.4. – electrical charge.5. Can donate a hydrogen ion.6. + electrical charge.8. ______ acid base pair.

11. Fundamental unit of matter.15. Has more or less electrons than protons.

5

Name ____________

5


ACIDS, BASES, AND SALTS from the Elements of Chemistry SeriesCreative Writing Story Ideas

Directions: Choose from one of the ideas listed below and write a story or dramatization. Include plotlines that follow scientific principles and key vocabulary terms.

1. Three students are experimenting with acids and bases. One carelessly spills acid on the hand of anotherstudent. Write a story focusing on the characters of the students and explain the incident.

2. It has been five years since a chemist knocked on the door of a remote farmhouse to explain to the farmerthat using fertilizer that gives the correct pH level to the soil could dramatically increase the yields of thefarm. Describe what has happened to the farmer and his family since that fateful day.

3. A group of students involved in a research project has discovered that acid rain is damaging the forests andaquatic life in a pristine wilderness near their home. They have traced the source of the pollution to a coal-fired power plant generating electricity for a nearby city. An appointment has been made for the students tobring these findings to a political committee responsible for pollution issues. One of the students has beenelected the spokesperson for the group. Write the speech that the student will give to the committee.

4. A research chemist has found a very strong acid that is almost 0 on the pH scale. The difficulty is that theacid is so strong, it eats through any container in which it is stored. Describe what happens.

5. An "evil" genius is plotting to take over the world by manipulating acids and bases. The forces of "good"uncover the plot and set in motion plans to neutralize the threatening acids and bases. Write a humorous filmscript or story that dramatizes the outrageous characters and describe the adventure.

6Name ____________

ACIDS, BASES, AND SALTS from the Elements of Chemistry SeriesVideo Quiz

Directions: Answer the following either true or false, or fill in the blank with the correct word tomake it true.

1. Both acids and bases are electrolytes—good conductors of electric current. T______ F______

2. Bases always react with metals. T______ F______

3. Acids react with bases so that the properties of both are lost to form water and a salt. This is called ____________.

4. Arrhenius defined acids as substances that generate hydroxide ions, OH¯, when dissolved in water.

T______ F______

5. Brønsted and Lowry defined a base as any substance that can accept a hydrogen ion. T______ F______

6. Both acids and bases are related to the concentration of ____________ ____________ present.

7. A strong acid is one that readily transfers H+

ions to water. T______ F______

8. A conjugate acid-base pair differs by several H+

ions. T______ F______

9. The pH scale is a measurement of the acidity and basicity of compounds. T______ F______

10. When rainfall has a reading on the pH scale lower than 5.6, it is called ____________ ____________.


7

Name ____________

7 ACIDS, BASES, AND SALTS from the Elements of Chemistry SeriesPost-Test

Directions: Fill in the blank with the appropriate term from the list below.

acid cation fission neutralanion conjugate fusion neutralizationatom electrolytes ion neutronatomic electrons litmus positivebase element negative proton

1. The process where acids and bases react so that both are lost to form water and a salt is called____________.

2. According to the definition, a ____________ is any substance that can accept a hydrogen ion.

3. A negatively charged ion is called an ____________.

4. Substances that are good conductors of electricity are called ____________.

True or FalseDirections: Fill in the blank with True or False. If the statement is false, change it to make the state-ment true. Rewrite the true statement in the space provided.5. __________ An ion is the same as a neutral atom.

6. __________ Acid rain is not harmful.

7. __________ According to Brønsted and Lowry, a base is any substance that can accept a hydrogen ion.

8. __________ A conjugate acid-base pair have similar chemical properties.

9. __________ A H+

ion has two electrons.

Essay SectionDirections: Answer the following questions in complete sentences. Use the back of this page or a sep-arate sheet of paper to complete your answers.

10. Describe the physical qualities of bases.

11. Explain the Brønsted/Lowry definition of acids and bases.

12. What is the importance of the pH scale?


from the six-part elements of chemistry...

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