CHAPTER 8 Acids, Bases, and Saltsmrwelling.weebly.com/uploads/2/1/9/6/21963578/ch.8_book.pdf · Acids, Bases, and pH > Describe the ionization of strong acids in water and the dissociation

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Acids, Bases,and Salts

C H A P T E R 8

Chapter Preview

1 Acids and BasesWhat Are Acids?What Are Bases?What Is pH?

2 Reactions of Acids with BasesAcid-Base ReactionsSalts

3 Acids, Bases, and Salts in the HomeCleaning ProductsAcids, Bases, and Salts in the Household

Acids, Bases,and Salts

Copyright © by Holt, Rinehart and Winston. All rights reserved.

Background Some kinds of ants can defend themselves with aquick squirt of highly irritating formic acid solution. These antsare often called stinging ants, but in fact the ants bite and thensquirt the acid into the wound. Formic acid was identified in1670 by a chemist who heated ants in a flask and collected thevapors given off. The name formic acid is from the Latin formica,meaning ant. Many other acids are also found in living things.

Acids also react with a type of chemical called bases. Inmany ways, acids and bases are chemical opposites. For exam-ple, the base calcium hydroxide can be used to treat lakes thatare too acidic. The reaction that neutralizes the lake is similar tothe reaction that happens when you take an antacid for an upsetstomach.

Activity 1 Cut a lemon in half. Squeeze the lemon over a cleandish to get about a teaspoon of juice. Dip a clean finger into thejuice, and taste it. Describe the taste. Do you think that lemonjuice is acidic or basic? Give reasons for your decision.

Activity 2 After you have tasted the lemon juice in Activity 1,add a teaspoon of water to it, and stir with your finger. With aclean, dry spoon, add 1/2 teaspoon of baking soda to the dilutedlemon juice. What happens to the juice and baking soda? Bakingsoda is a basic substance. What evidence do you see that achemical reaction takes place?

ACTIVITYACTIVITYFocusFocus

Pre-Reading Questions1. The orange is known as a citrus fruit

because it contains citric acid. What other foods may contain citric acid?

2. Bee venom is also acidic. How might a solution of baking soda in water reduce the pain of a bee sting?

255

www.scilinks.orgTopic: Acids and Bases SciLinks code: HK4163

Some species of ants pro-duce formic acid and injectit into their victims whenthey bite. The helicopter isadding a base to an acidiclake to neutralize it.

Copyright © by Holt, Rinehart and Winston.All rights reserved.

Acids, Bases, and pH> Describe the ionization of strong acids in water and the

dissociation of strong bases in water.> Distinguish between solutions of weak acids or bases and

solutions of strong acids or bases.> Relate pH to the concentration of hydronium ions and

hydroxide ions in a solution.

Does the thought of eating a lemon make your mouth puckerand your saliva flow? You know to expect that sour, piercing

taste that can sometimes make you shudder. Eating a lime or adill pickle may cause you to have a similar response.

What Are Acids?Each of the foods shown in Figure 1 tastes sour because it con-tains an Several fruits, including lemons and limes, con-tain citric acid. Dill pickles are soaked in vinegar, which containsacetic acid. Other acidic foods include apples, which containmalic acid, and grapes, which contain tartaric acid.

When acids dissolve in water, they ionize, which means thatthey form ions. Hydrogen ions, H�, attach to water molecules toform hydronium ions, H3O+. These hydronium ions are respon-sible for the sour taste you experience. respond tothe concentration of hydronium ions in water by changing color.Blue litmus paper contains an indicator that can help you deter-mine if a substance is an acid. Acids turn blue litmus paper red,as shown in Figure 1.

Indicators

acid.

O B J E C T I V E S

SECTION

1

256 C H A P T E R 8

K E Y T E R M S

acidindicatorelectrolytebasepH

▲

acid any compound thatincreases the number ofhydronium ions when dis-solved in water

indicator a compound thatcan reversibly change colordepending on the pH of thesolution or other chemicalchange

▲▲

Figure 1Lemons, limes, and dill picklestaste sour because they containacids. Acids, such as the citric acidin lemon juice, turn blue litmuspaper red.


Strong acids ionize completelyAll acids ionize when dissolved in water. The ionization processshown in Figure 2A occurs when nitric acid is added to water. Thesingle arrow pointing to the right shows that nitric acid ionizescompletely in water. When the acid ionizes, it forms hydroniumions and nitrate ions. These charged ions are able to movearound in the solution and conduct electricity, as you see inFigure 2B. A substance that conducts electricity when dissolved inwater is an

Solutions of some acids, such as nitric acid, conduct electric-ity well. Nitric acid, HNO3, is a strong acid because it ionizescompletely in water. Other strong acids behave similarly to nitricacid when dissolved in water. A solution of sulfuric acid in water,for example, conducts electric current in car batteries. Strongacids are strong electrolytes because solutions of these acids haveas many hydronium ions as the acid can possibly form.

Weak acids do not ionize completelySolutions of weak acids, such as acetic acid, CH3COOH, do notconduct electricity as well as nitric acid. When acetic acid isadded to water, the equilibrium shown in Figure 3A is reached.

When acetic acid is dissolved in water, some molecules ofacetic acid combine with water molecules to form ions. Many ofthe ions then recombine to form molecules of acetic acid.Because there are fewer charged ions in a solution of acetic acid,it does not conduct electricity very well, as shown in Figure 3B.Acetic acid and other weak acids are weak electrolytes.

electrolyte.

A C I D S , B A S E S , A N D S A L T S 257

Nitric acid Water Hydronium ion Nitrate ion

+ ++

–

→

Figure 2

Nitric acid, HNO3, is a strongelectrolyte and a strong acidbecause it ionizes completely inwater to form hydronium, ionsH3O�, and nitrate ions, NO3

�.

B

electrolyte a substance thatdissolves in water to give asolution that conducts anelectric current

▲

A

Acetic acid, CH3COOH, is aweak acid and a weak electrolytebecause it ionizes only partially inwater to form hydronium ions,H3O�, and acetate ions, CH3COO–.

B+ +

+

–

Acetic acid Water Hydronium ion Acetate ion

→→

Figure 3

A


Any acid can be dangerous in a concentrated formSome examples of common strong and weak acids and their usesare listed in Table 1. Acids are used in many manufacturingprocesses and are necessary to many organisms even thoughstrong acids can damage living tissue. For example, your stom-ach normally contains a dilute solution of hydrochloric acid thathelps you digest food, but concentrated hydrochloric acid canburn your skin.

Even weak acids are not always safe to handle. Most vinegaris a 5% solution of acetic acid in water, but concentrated aceticacid can damage the skin, and the vapors are harmful to the eyes,mouth, and lungs. To be safe, always wear safety goggles, gloves,and a laboratory apron when working with acids.

What Are Bases?Like acids, all share common properties. Bases have a bit-ter, soapy taste, and solutions of bases feel slippery. Figure 4shows some common household substances that contain bases.Like solutions of acids, solutions of bases contain ions and canconduct electricity. Some bases contain hydroxide ions, OH�, butothers do not. Bases that do not contain hydroxide ions will reactwith water molecules to form hydroxide ions. Bases cause indi-cators to change color, such as turning red litmus paper blue.

bases

258 C H A P T E R 8

Table 1 Some Common Acids

Hydrochloric HCl strong cleaning masonry; treating metal before acid plating or painting; adjusting the pH of

swimming pools

Sulfuric acid H2SO4 strong manufacturing fertilizer and chemicals;most used industrial chemical; theelectrolyte in car batteries

Nitric acid HNO3 strong manufacturing fertilizers and explosives

Acetic acid CH3COOH weak manufacturing chemicals, plastics, and pharmaceuticals; the acid in vinegar

Formic acid HCOOH weak dyeing textiles; the acid in stinging ants

Citric acid H3C6H5O7 weak manufacturing flavorings and soft drinks; the acid in citrus fruits (oranges, lemons, limes)

Acid Formula Strength Uses for the acid

base any compound thatincreases the number ofhydroxide ions when dis-solved in water

▲

Figure 4These household items are basesbecause they produce OH� ionsin water solution.


Many common bases contain hydroxide ionsStrong bases are ionic compounds that contain a metal ion and ahydroxide ion. These strong bases are also known as metalhydroxides. When a metal hydroxide is dissolved in water, themetal ions and the hydroxide ions dissociate, or separate.

For example, sodium hydroxide, NaOH, is a metal hydroxidethat is found in some drain cleaners. Solutions of sodiumhydroxide conduct electricity well, so sodium hydroxide is astrong electrolyte. The dissociation of sodium hydroxide in wateris shown below.

NaOH → Na� � OH�

Some metal hydroxides, such as calcium hydroxide and mag-nesium hydroxide, are not very soluble in water, but the ions inthe part of the metal hydroxide that does dissolve separate com-pletely. Calcium hydroxide is used to treat soil that is too acidic.Other useful bases are listed in Table 2.

Like acids, bases can be very dangerous in concentratedform, and in the case of bases such as sodium hydroxide andpotassium hydroxide, bases can be dangerous even in fairlydilute form. Because bases attack living tissue very rapidly, basesare in some ways more dangerous than acids. To protect yourselfwhen working with bases in the laboratory, always wear safetygoggles, gloves, and a laboratory apron. If possible, work withvery dilute bases instead of concentrated ones.


Potassium KOH strong manufacturing soap; absorbing carbonhydroxide (potash) dioxide from flue gases; dyeing products

Sodium NaOH strong manufacturing soap; refining petroleum; hydroxide (lye) cleaning drains; manufacturing synthetic

fibers

Calcium Ca(OH)2 strong treating acidic soil; treating lakes pol-hydroxide luted by acid precipitation; making

mortar, plaster, and cement

Ammonia NH3 weak fertilizing soil; manufacturing other fertilizers; manufacturing nitric acid; making cleaning solutions

Methylamine CH3NH2 weak manufacturing dyes and medicines; tanning leather

Aniline C6H5NH2 weak manufacturing dyes and varnishes; used as a solvent

Base Formula Strength Uses for the base

Table 2 Some Common Bases


Other bases ionize in water to form hydroxide ionsAmmonia, like other bases, forms hydroxide ions when it dis-solves in water. But ammonia does not contain hydroxide ions.Instead, it forms hydroxide ions with water through an ioniza-tion process, shown in Figure 5. In this process, water acts as anacid and donates a hydrogen ion to ammonia to form an ammo-nium ion, NH4

�, and leaves a hydroxide ion, OH�, behind. A solution of ammonia in water is a poor conductor of elec-

tricity. This shows that only some of the ammonia moleculesactually become ammonium ions when the ammonia dissolves.So, an ammonia solution consists mostly of water and dissolvedammonia, along with a few ammonium ions and hydroxide ions.Ammonia is a much weaker base than potassium hydroxide,which is a metal hydroxide that dissociates completely.

260 C H A P T E R 8

Figure 5Ammonia produces hydrox-ide ions in water throughionization. An ammoniamolecule accepts H� ionsfrom water to form ammo-nium ions, NH4

�, andhydroxide ions, OH�.

+ +

+ –

Ammonia Water Ammonium ion Hydroxide ion

Materials

Which household substances are acidic, which are basic, and which are neither?

✔ baking powder ✔ milk ✔ white vinegar ✔ disposable pipets✔ baking soda ✔ mineral water ✔ dishwashing liquid or eyedroppers✔ several 50 mL ✔ bleach ✔ soft drinks ✔ laundry detergent

beakers ✔ blue litmus ✔ mayonnaise ✔ tap water✔ pipet bulbs paper ✔ red litmus paper

SAFETY CAUTION Wear safety goggles, gloves,and a laboratory apron. Never pipet anything bymouth.

1. Prepare a sample of each substance you willtest. If the substance is a liquid, pour about 5 mL of it into a small beaker. If the substance is a solid, place a small amount of it in a beaker, and add about 5 mL of water. Label each beakerclearly with the name of the substance that is in the beaker.

2. Use a pipet to transfer a drop of liquid from oneof the samples to red litmus paper. Then transfer

another drop of liquid from the same sample toblue litmus paper. Record your observations.

3. Repeat step 2 for each sample. Be sure to use aclean pipet to transfer each sample.

Analysis1. Which substances are acidic? Which are basic?

How did you determine this?

2. Which substances are not acids or bases? Howdid you determine this?

→→


What Is pH?You can tell if a solution is acidic or basic by using an indicator,such as litmus paper. But to determine exactly how acidic orbasic a solution is, you must measure the concentration of hydro-nium (H3O�) ions. The of a solution indicates its concentra-tion of H3O�ions. The pH of a solution is often critical. Forexample, enzymes in your body work only in a narrow pH range.

pH values correspond to the concentration of hydronium ionspH is a measure of the H3O� concentration in a solution, but pHalso indicates hydroxide ion (OH�) concentration. So a pH valuecan tell you how acidic or basic a solution is. A pH value can eventell you if a solution is neutral, or neither an acid nor a base.

Typically, the pH of solutions ranges from 0 to 14, as shownin Figure 6. In neutral solutions, or in substances such as purewater, the concentration of hydronium ions equals the concen-tration of hydroxide ions, and the pH is 7. Solutions that have apH of less than 7 are acidic. In acidic solutions, such as apple juice,the concentration of hydronium ions is greater than the concen-tration of hydroxide ions. Solutions that have a pH of greaterthan 7 are basic. In basic solutions, the concentration of hydrox-ide ions is greater than the concentration of hydronium ions.

pH


The term pH originates from the French words pouvoirHydrogène, which means “the power of hydrogen.”

V

pH a value used to expressthe acidity or alkalinity of asolution

▲

Figure 6The pH of a solution is easilymeasured by moistening a pieceof pH paper with the solution andthen comparing the color of thepH paper with the color scale onthe dispenser of the pH paper.

NEUTRALMore hydroxide ionsMore hydronium ions

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Batteryacid

Stomach acid

Blackcoffee

Bakingsoda

Antacid (when dissolved in water)

DraincleanerApple

juice

Purewater

Hand soap

Householdammonia

OH–H3O+ H3O+ = OH–


The concentration of a strong acid allows you to calculate pHWhen you describe the concentration of a substance in a solu-tion, you probably write the concentration as a molarity (M), orthe number of moles of the substance per liter of solution. Forexample, the hydronium ion (H3O�) concentration of pure waterat 25°C is 0.000 000 1 mol/L, or 10�7 M.

When the H3O� concentration of a solution can be written asa power of 10, the pH is the negative of the power of 10 used todescribe the concentration of hydronium ions. For example, thepH of pure water is 7, so the concentration of hydronium ions inwater is 10–7 M. The pH of apple juice is about 3, so the concen-tration of H3O� in apple juice is 10–3 M.

If you know the concentration of a solution of a strong acid, youcan calculate the pH of the solution. When a strong monoproticacid ionizes in a solution, one hydronium ion is formed for eachparticle of acid that dissolves. So the concentration of hydroniumions in a solution of strong acid is the same as the concentration ofthe acid itself, and this information allows you to find the pH ofthe solution.

262 C H A P T E R 8

www.scilinks.orgTopic: pHSciLinks code: HK4103

Did you know that the con-centration of hydronium ionsand the concentration of hy-droxide ions are related? Inany solution made with water,the more hydronium ionsthere are (the more acidic thesolution is), the fewer hydrox-ide ions there are (the lessbasic the solution is).

PracticeHINT

Math SkillsMath Skills

> If a solution contains a base,you should expect the pH tobe greater than 7. If the solu-tion contains an acid, the pHwill be less than 7.

> To find the concentration ofa solution of strong acidfrom its pH, multiply the pHvalue by –1. Then use theresult as a power of 10. Theresult is the concentration ofthe acid in moles per liter(mol/L).

Determining pH Determine the pH of a 0.0001 M solution ofthe strong acid HCl dissolved in water.

List the given and unknown values.Given: concentration of HCl in solution = 0.0001 MUnknown: pH

Determine the molar concentration of hydroxide ions.concentration of HCl in solution = 0.0001 MHCl is completely ionized into H3O+ and Cl– ions.concentration of H3O+ ions in solution = 0.0001 M = 1 � 10–4 M

Convert the H3O� concentration to pH.concentration of H3O+ ions = 1 � 10–4 MpH = –(–4) = 4

Determining pH

1. Calculate the pH of a 1 � 10–4 M solution of HBr, a strong acid.

2. Determine the pH of a 0.01 M solution of HNO3, a strong acid.

3. Nitric acid, HNO3, is a strong acid. The pH of a solution of HNO3

is 3. What is the concentration of the solution?

3

2

1

PracticePractice


Small differences in pH mean larger differences in acidityBecause pH is the negative of the power of 10 of hydronium ionconcentration, small differences in pH mean larger differences inthe hydronium ion concentration. For example, the pH of applejuice differs from the pH of coffee by two pH units, so apple juiceis 102, or 100 times, more acidic than coffee. Likewise, coffee isabout 103, or 1000 times, more acidic than antacid tablets, whichform a base with a pH of about 8 when dissolved in water.

pH can be measured in more than one waypH paper contains several indicators that change color at differ-ent pH values. pH may also be measured with a pH meter, asshown in Figure 7. Because ions in a solution have an electriccharge, a pH meter can measure pH by determining the electriccurrent created by the movement of the ions in the solution. Ifyou use a pH meter properly, you can determine the pH of a solu-tion more precisely than is possible if you use pH paper.


S E C T I O N 1 R E V I E W

1. Explain how a strong acid and a weak acid behave differ-ently when each is dissolved in water.

2. Compare the ionization of a weak acid in water to the ioni-zation of a weak base in water.

3. Write the chemical equation for the self-ionization of water.

4. Classify the following solutions as acidic, basic, or neutral.a. a soap solution, pH = 9b. a sour liquid, pH = 5c. a solution that has four times as many hydronium ions

as hydroxide ionsd. pure water

5. Arrange the following substances in order of increasingacidity: vinegar (pH = 2.8), gastric juices from inside yourstomach (pH = 2.0), and a soft drink (pH = 3.4).

6. Critical Thinking A solution of an acid in water has a pH of 4,which is slightly acidic. Is this a solution of a weak acid?Explain your answer.

7. What is the pH of a 0.01 M solution of the strong acidHClO4, perchloric acid?

Math SkillsMath Skills

S U M M A R Y

> Acids are substances thattaste sour, turn blue litmuspaper red, and form hydro-nium ions when they dis-solve in water.

> Strong acids are strongelectrolytes because theyionize completely in water.

> Weak acids are weakelectrolytes because theyionize only slightly in water.

> Bases have a slippery feel,have a bitter taste, turn redlitmus paper blue, and pro-duce hydroxide ions whenthey dissolve in water.

> The pH of a solution of astrong acid can be found ifyou know the concentra-tion of the solution.

Figure 7A pH meter measures an electriccurrent that results from differ-ences in H3O� concentrations.


O B J E C T I V E S

SECTION

2

264 C H A P T E R 8

> Write ionic equations for neutralization reactions.> Identify the products of a neutralization reaction.> Describe the composition of a salt.

Reactions of Acids with Bases

Have you ever used an antacid to relieve the symptoms of anupset stomach or so-called heartburn? Heartburn has noth-

ing to do with your heart. Heartburn occurs when the stomach’snatural solution of hydrochloric acid (HCl) irritates the lining ofthe esophagus. The antacid contains a base that reacts with theacid to reduce the acidity of the solution and soothe your stomach.

Acid-Base ReactionsA reaction between an acid and a base is a

An example of neutralization is the reaction of HCland magnesium hydroxide, which is an antacid and a base.

Neutralization is an ionic reactionA solution of a strong acid, such as hydrochloric acid, ionizescompletely, as shown below.

HCl � H2O → H3O� � Cl�

In a similar way, a solution of a strong base, such as sodiumhydroxide, dissociates completely, as shown below.

NaOH → Na� � OH�

If the two solutions of equal concentrations and equal volumesare combined, the following neutralization reaction takes place:

H3O� � Cl� � Na� � OH� → Na� � Cl� � 2H2O

The Na� and Cl� ions are called spectator ions because they arelike spectators watching on the sidelines. These ions do notchange during the reaction between H3O� and OH�. As you cansee in Figure 8, energy is also released in the reaction of Na and Cl.

reaction.neutralization

K E Y T E R M S

neutralization reactionsalt

▲

neutralization reactionthe reaction of the ions thatcharacterize acids (hydroniumions) and the ions that charac-terize bases (hydroxide ions)to form water molecules anda salt

▲

Figure 8When HCl reacts with NaOH,sodium chloride is produced andenergy is released.



Strong acids and bases react to form water and a saltIf you include only the substances that react during neutraliza-tion, the equation can be written as follows:

H3O� � OH� → 2H2O

When an acid reacts with a base, hydronium ions react withhydroxide ions to form water. The other ions—positive ions fromthe base and negative ions from the acid—form an ionic com-pound called a such as sodium chloride. Salts are ioniccompounds that are often soluble in water, as you can see inFigure 9.

Not all neutralization reactions produce neutral solutionsReactions between acids and bases do not always produce neu-tral solutions. The final pH of the solution depends on theamounts of acid and base that are combined. The pH alsodepends on whether the acid and base are strong or weak.

If a strong acid, such as nitric acid, reacts with an equalamount of a weak base, such as sodium hydrogen carbonatefrom an antacid tablet, the resulting solution will still be acidic.A similar situation occurs when a strong base reacts with a weakacid. When a strong acid reacts with an equal amount of a weakbase, the resulting solution will be acidic.

salt,

Chloride ion,Cl�

Hydronium ion,H3O�

Hydroxide ion,OH�

Water molecule,H2O

Sodium ion,Na�

Figure 9When a solution of HCl reacts witha solution of NaOH, the reactionproduces water and leavessodium and chloride ions in solu-tion. When the water is evapo-rated, the sodium and chlorideions crystallize to form puresodium chloride.

salt an ionic compound thatforms when a metal atom or a positive radical replaces thehydrogen of an acid

▲


Titrations are neutralization reactionsWhen an acid solution is added to a basic solution, aneutralization reaction occurs. If you know the concen-tration of the acid solution or the basic solution, a titra-tion can help you determine the concentration of theother solution. A titration is the process of graduallyadding one solution to another solution in the presenceof an indicator to determine the concentration of one ofthe solutions.

In a titration, an indicator is used that changes colorwhen the original amount of the base in solution isequal to the amount of the acid added to the solution.For example, when a strong acid is titrated with astrong base, an indicator called bromthymol blue is usedbecause bromthymol blue changes color when the solu-tion reaches a pH of about 7, as shown in Figure 10.

When a strong acid is dissolved, it ionizes completely to formhydronium ions. When a strong base dissolves, it forms as manyhydroxide ions as possible. And as you have learned, hydroniumions and hydroxide ions combine in a neutralization reaction. Ifthe number of hydronium ions is equal to the number of hydrox-ide ions in a solution, the product of the reaction will be neutral.The equivalence point in a titration of a strong acid with a strongbase is reached when the original amount of the acid equals theoriginal amount of the base and occurs at pH 7. Figure 11 showsthe change in pH during the titration of nitric acid with sodiumhydroxide.

The equivalence point is not always neutralTitrations can also be carried out with a strong acid and a weakbase, or with a weak acid and a strong base. In these cases, how-ever, the equivalence point will not be at pH 7. For example,when 1 mol of acetic acid, a weak acid, is dissolved in water, onlysome of the molecules of the acid ionize to form H3O� ions.When 1 mol of sodium hydroxide is added to water, it dissociatesto form 1 mol of OH� ions because sodium hydroxide is a strongbase. When the neutralization reaction takes place betweenacetic acid and sodium hydroxide, there are OH� ions left over.

When there are OH� ions left over, a neutralization reactiondoes not produce a neutral solution. Neutralization occurs whenwater is formed from H3O� ions and OH� ions, but if there areany hydroxide ions left over, the solution will still be basic. Asimilar situation occurs when a strong acid is titrated with aweak base, but in this case the product is acidic and has a pH ofless than 7.

pH

mL base added 0 25

2

4

050

6

8

100

14

75

10

12Equivalence

point

Figure 10Bromthymol blue is an indicatorthat changes color between a pHof 6.0 and 7.6. It is ideal for a titra-tion involving a strong acid and astrong base.

Figure 11When a strong acid, such as nitricacid, is titrated with a strong base,the pH of the solution changesrapidly when the equivalencepoint is reached.

266 C H A P T E R 8 Copyright © by Holt, Rinehart and Winston. All rights reserved.

SaltsWhen you hear the word salt, you probably think of white crys-tals that you sprinkle on food. But to a chemist, a salt can bealmost any combination of cations and anions, except forhydroxides and oxides, which are bases.

Sodium chloride has many different usesCommon table salt contains sodium chloride, NaCl, which is anionic compound that can be formed from the reaction ofhydrochloric acid with sodium hydroxide. NaCl is the source ofmost of the sodium in your diet. It is widely used to season andpreserve food. Most NaCl in the United States comes from under-ground deposits that were left when ancient seas dried up.

NaCl is also used in ceramic glazes, soap manufacturing,home water softeners, highway de-icing, and fire extinguishers.Many other salts also contain sodium, as you can see in Table 3below.

Salts are all around usSalts can be formed by acid-base neutralization, but more often,they are formed from other salts. Another familiar example of asalt is baking soda, sodium hydrogen carbonate. Photographicfilm contains the salts silver bromide and silver iodide, which aresensitive to light. Ordinary soaps and detergents are also examplesof salts. Figure 12 shows a salt that is used in medical diagnosis.

Salt Formula Uses

Aluminum sulfate Al2(SO4)3 purifying water; used in antiperspirants

Ammonium sulfate (NH4)2SO4 flameproofing fabric; used as fertilizer

Calcium chloride CaCl2 de-icing streets and highways; used in some kinds of concrete

Potassium chloride KCl treating potassium deficiency; used as table-salt substitute

Sodium carbonate Na2CO3 manufacturing glass; added to wash to soften water

Sodium hydrogen NaHCO3 treating upset stomach; ingredient in baking powder; carbonate used in fire extinguishers

Sodium stearate NaOOCC17H34 typical example of a soap

Sodium lauryl sulfonate NaSO3C12H25 typical example of a detergent

Table 3 Some Common Salts

Figure 12The salt barium sulfate, BaSO4, isa highly insoluble salt that blocksX rays. After barium sulfate isplaced into the large intestine, theform of the intestine shows uplighter on an X-ray photo.

A C I D S , B A S E S , A N D S A L T S 267Copyright © by Holt, Rinehart and Winston. All rights reserved.

Salts are useful substancesYou have probably seen a lot of chalk since you enteredschool, but did you know that chalk is a salt? Chalk is oneform of the salt calcium carbonate, CaCO3, which alsomakes up limestone and marble. It is likely that the walls inyour house are made of slabs of gypsum, which is one formof the salt calcium sulfate, CaSO4.

You often hear that a healthful diet should include min-erals such as potassium, sodium, calcium, magnesium, iron,phosphorus, and iodine. However, ingesting these nutrientsin the form of free elements is not very common. Instead,you get ions of these elements in their ionic form from salts.You need calcium ions, Ca2�, for strong bones and teeth andfor proper function of nerves and muscles. The correct pro-portion of potassium ions, K�, and sodium ions, Na�, is cru-cial for transmission of nerve impulses, even in insects, suchas those shown in Figure 13. Phosphorus, in the form ofphosphate ions, PO4

3�, is needed for many processes in liv-ing cells, from transporting energy to the reproduction of thegenetic code.

268 C H A P T E R 8


1. Write the chemical equation for the neutralization of nitricacid, HNO3, with magnesium hydroxide, Mg(OH)2, firstwith spectator ions and then without spectator ions.

2. Determine which acid and which base you would combineto form the salt aluminum sulfate, Al2(SO4)3.

3. Identify the spectator ions in the neutralization of lithiumhydroxide, LiOH, with hydrobromic acid, HBr.

4. Predict whether the reaction of each of the following acidsand bases will yield an acidic, a basic, or a neutral solution.Explain your answer for each.a. sulfuric acid, H2SO4, and ammonia, NH3

b. formic acid, HCOOH, and potassium hydroxide, KOHc. nitric acid, HNO3, and calcium hydroxide, Ca(OH)2

5. Critical Thinking A classmate observes a neutralization reac-tion between an acid and a base. After the reaction is com-plete, your classmate is surprised to find that the pH of theresulting solution is 4, not 7, the pH of a neutral solution.What can you tell your classmate to help them understandwhat happened?

S U M M A R Y

> Acids and bases react witheach other in a processcalled neutralization.

> Neutralization is a reactionbetween an acid and a baseto form water and a salt.

> Neutralization reactionsbetween weak acids andstrong bases result in basicsolutions.

> Neutralization reactionsbetween strong acids andweak bases result in acidicsolutions.

> Salts are ionic substancescomposed of cations andanions other than oxide orhydroxide.

Figure 13These butterflies can obtain thesalt they need from the driedsweat on an old sneaker.


> Describe the chemical structures of soaps and detergentsand explain how they work.

> Describe the chemical composition of bleach and its uses.> Describe how an antacid reduces stomach acid.> Identify acidic and basic household products and their

uses.

Acids, Bases,and Salts in the Home

A s you have seen, you won’t find acids, bases, and salts onlyin a laboratory. Many items in your own home, such as

soaps, detergents, shampoos, antacids, vitamins, sodas, andjuices in your kitchen are examples of household products thatcontain acids, bases, and salts.

Cleaning ProductsIf you work on an oily bicycle chain or if you’ve been eatingpotato chips, water alone will not remove the greasy film fromyour hands. Water will not work because it doesn’t mix withgrease or oil. Something else must be added to water to improveits ability to clean.

Soaps allow oil and water to miximproves water’s ability to clean because it can dissolve in

both oil and in water. This property allows oil and water to forman emulsion that can be washed away by rinsing. For example,when you are washing your face with soap, as the girl in Figure 14is, the oil on your face is emulsified by the soapy water. The wateryou rinse with carries away both the soap and unwanted oil toleave your face clean.

Soaps are salts of sodium or potassium and fatty acids, whichhave long hydrocarbon chains. Soaps are made through a reac-tion of animal fats or vegetable oils with a solution of sodiumhydroxide or potassium hydroxide. The products of the reactionare soap and an alcohol called glycerol.

Soap

SECTION

3


K E Y T E R M S

soapdetergentdisinfectantbleachantacid

▲

soap a substance that is usedas a cleaner and that dissolvesin water

▲

Figure 14When you wash with soap, youcreate an emulsion of oil dropletsspread throughout water.

O B J E C T I V E S


How soap removes greaseSoap is an ionic compound. Its negative ion is along hydrocarbon chain of the soap anion witha carboxylate group (�COO�) at one end. Forevery negatively charged end, there is a positivesodium or potassium ion.

Soap is able to remove grease and oilbecause the cations and the negatively chargedends of the chains (�COO�) dissolve in water,while the hydrocarbon chains dissolve in oil.Soap acts as an emulsifier by surroundingdroplets of oil, as shown in Figure 15. Thisaction causes the droplets of oil to stay sus-pended in water. When you are washing yourhands with soap, you probably rub themtogether. Rubbing your hands together actuallyhelps clean them. When you do this, you liftmost of the emulsion of grease and waterinto the lather where it can be rinsed into the sink.

Detergents have replaced soap in many usesAs useful as soap is for cleaning, it does not work well in hardwater, that is, water containing the dissolved ions Mg2�, Ca2�,and Fe3�. These cations combine with the fatty acid anions ofsoap to form an insoluble salt called soap scum. This soap scumsettles out on clothing, dishes, your skin, and your hair. The scumalso makes a ring around the bathtub or washbasin. To preventthis problem, are used instead of soap to washclothes and dishes. Most shampoos, liquid hand soaps, and bodywashes are actually detergents, not soap.

Detergents are sodium, potassium, and sometimes ammo-nium salts. Like anions in soaps, the anion in detergents are com-posed of a long hydrocarbon chain that has a negatively chargedend. But the charged end of a detergent is a sulfonate group(�SO3

�), not a carboxylate group. These sulfonate ions do notform scum with the ions in hard water. Detergents are also differ-ent from soaps because their hydrocarbon chains are made frompetroleum products instead of from animal fats or plant oils.

Because soaps and detergents act in the same way, Figure 15represents detergents as well as soaps. The long hydrocarbonchains are soluble in oil or grease. The sulfonate ends are highlysoluble in water. Water molecules attract the charged sulfonategroup and keep the oil droplet suspended among the watermolecules.

detergents

270 C H A P T E R 8

detergent a water-solublecleaner that can emulsify dirtand oil

▲

Figure 15The charged ends of soap ordetergent dissolve in water, andthe hydrocarbon chains dissolve in oil, keeping the oil droplet insuspension.

Connection toSOCIAL STUDIESSOCIAL STUDIES

People have used soap for thousands of years.Ancient Egyptians took baths regularly with

soap made from animal fats or vegetable oils and basic solutions of alkali-metal compounds.According to Roman legend, people discovered thatthe water in the Tiber River near Mount Sapo wasgood for washing. Mount Sapo was used for elabo-rate animal-sacrifice rituals, and the combination ofanimal fat and the basic ash that washed down themountain made the river soapy.

Making the Connection1. The process of making soap is sometimes

referred to as saponification. How does thisword relate to the Roman soap legend?

2. Homemade soap can be made from hog fatand ashes. Which material provides the baseneeded to make the soap?

Water-solubleend of chain

Oil-solubleend of chain

Sodium cation


Many household cleaners contain ammonia Ammonia solutions, such as the ones shown in Figure 16, are alsoeffective cleaners. Household ammonia is a solution of ammoniagas in water. Recall that ammonia is a weak base because it ion-izes only slightly in water to form ammonium ions and hydrox-ide ions. The hydroxide ions make the ammonia solution basic,as shown in the reaction below.

NH3 � H2O ←→ NH4� � OH�

Although the concentration of hydroxide ions is very low in anammonia solution, enough of the ions are available to help emul-sify thin layers of oily dirt, such as fingerprints and oily smears.In addition, many ammonia cleaners contain alcohols, deter-gents, and other cleaning agents.

Bleach can eliminate stains A is a substance that kills bacteria and viruses.Household a very strong disinfectant, is a basic solutionof sodium hypochlorite, NaOCl. You are probably familiar withthe ability of bleach to remove colors and stains.

Bleach does not actually remove the substance causing thestain. Instead, it changes the substance to a colorless form.This bleaching action is carried out by the oxygen atom in thehypochlorite ion, ClO�.

If an acid is added to a bleach solution, the acid reacts withthe hydroxide ions, and the reaction reverses, giving off deadlychlorine gas. For this reason, you should never mix bleach withan acid, such as vinegar. Also, ammonia and bleach should not bemixed because noxious chloramine gas, NH2Cl, is formed.

bleach,disinfectant


disinfectant a chemicalsubstance that kills harmfulbacteria or viruses

bleach a chemical com-pound used to whiten ormake lighter, such as hydro-gen peroxide or sodiumhypochlorite

▲▲

Figure 16Basic solutions of ammonia, suchas these, can clean away lightgrease smears, such as fingerprints.

2. Gently touch the drop of water with the tip of the toothpick. What happens to thedrop of water?

3. Now dip the tip of the toothpick in liquiddetergent.

4. Gently touch the drop of water with the tipof the toothpick after it has been dipped indetergent. What happens to the drop ofwater? How could this action help waterclean away dirt?

QuickQuickQuick ACTIVITYACTIVITY

Detergents help break up oil into droplets that canbe washed away by water. Detergents also breakup the surface tension of water so that it can wetmaterials more easily. In this activity, you willdemonstrate this effect using a piece of wax paper,a drop of water, a toothpick, and liquid detergent.

1. Lay some wax paper on a flat surface, andput a drop of water on it. Does the waterwet the surface of the wax paper? How canyou tell?

Detergents


Acids, Bases, and Salts in the HouseholdYou probably have taken many of the acidic and basic materialsin your home for granted. For example, many of the clothes inyour closet get their color from acidic dyes. These dyes aresodium salts of organic compounds that contain the sulfonic acidgroup (�SO3H) or the carboxylic acid group (�COOH). If youhave ever had an upset stomach because of excess stomach acid,you may have taken an antacid tablet to feel better. The antacidmade you feel better because it neutralized the excess stomachacid. Many other useful products in your home are also acids orbases.

Many healthcare products are acids or basesIn the morning before school, you may drink a glass of orangejuice that contains vitamin C. Ascorbic acid is the chemcial namefor vitamin C, which your body needs to grow and repair boneand cartilage. Both sodium hydrogen carbonate and magnesiumhydroxide (milk of magnesia) can be used as Antacidsare basic substances that you swallow to neutralize stomach acidwhen you have an upset stomach. Figure 17 shows how adding anantacid tablet to an acidic solution changes the pH of the solu-tion. A similar reaction (without the color change) takes place inyour stomach when you take an antacid.

antacids.

272 C H A P T E R 8

www.scilinks.orgTopic: Acids and Bases

at HomeSciLinks code: HK4003

antacid a weak base thatneutralizes stomach acid

▲

Materials

What does an antacid do?

✔ plastic stirrer ✔ red litmus paper ✔ spoon✔ wax paper ✔ 150 to 200 mL beakers (2) ✔ blue litmus paper✔ several varieties of ✔ pipet bulbs ✔ disposable pipets

antacid tablets ✔ vinegar

1. Pour 100 mL of water in abeaker. Add vinegar onedrop at a time while stir-ring. Test the solution with litmus paper aftereach drop is added. Record the number of dropsit takes for the solution to turn blue litmus paperbright red.

2. Use the back of a spoon to crush an antacid tabletto a fine powder on a piece of wax paper. Pour100 mL of water in the second beaker, add thepowdered tablet, and stir until a suspension forms.

3. Use litmus paper to find out whether the mixtureis acidic, basic, or neutral. Record your results.

4. Now add vinegar to the antacid mixture.Record the number of drops it takes to reactwith the antacid and turn the blue litmuspaper bright red. Compare this solution withthe solution that has only vinegar and water.Compare the brand of antacid you tested withthe brands of other groups.

Analysis1. How does an antacid work to relieve the pain

caused by excess stomach acid?

2. Of the brands that were tested, which brandworked the best? Explain your reasoning.


Shampoos are adjusted for an ideal pHShampoos can be made from soap. But if they are, they can leavesticky soap scum on your hair if you happen to live in an areathat has hard water. Most shampoos today are made from deter-gents and are able to remove dirt as well as most of the oil fromyour hair without leaving soap scum, even when they are usedwith hard water. Shampoo is not meant to remove all of the oilfrom your hair. Some oil is needed to give your hair shine and tokeep it from becoming dry and brittle.

The appearance of your hair is greatly affected by the pH ofthe shampoo you use. Hair—which consists of strands of a pro-tein called keratin—looks best when it is kept at either a slightlyacidic pH or very close to neutral. If a shampoo is too basic, itcan cause strands of hair to swell, which gives them a dull, life-less appearance. Shampoos are usually pH balanced, whichmeans that they are made to be in a specific pH range. The pH ofmost shampoos is between 5 and 8. Shampoos that have higherpH values are more effective in cleaning oil from your hair.Shampoos that have lower pH values protect dry hair.

Acids keep fruit fresh longerSome cut fruits slowly turn brown when they are exposed to air,such as the right side of the cut apple shown in Figure 18. Thishappens because certain molecules in the apple are oxidized toform darker substances. Both sides of the apple in Figure 18 werecut at the same time, so why does the left side of the apple looklike it was just cut? The left side was moistened with lemon juiceshortly after it was cut. The citric acid in lemon juice helpsantioxidants in the apple that react with oxygen before the oxy-gen can react with other substances in the apple. Vitamin C isanother example of a natural antioxidant.


Figure 17Stomach acid has about the sameconcentration of HCl as the solu-tion in the flask in the left photo.When an antacid tablet reacts withthe acid, the pH increases to aless acidic level, as shown in thephoto on the right.

The fibrous protein keratinbuilds up in the outermostcells of your epidermis, theouter layer of your skin.Keratin in these cells makesthe skin tough and almostcompletely waterproof.Keratin forms callouses inplaces on the skin where it is rubbed.

The horns, hoofs, claws,feathers, and scales of ani-mals grow from the sametype of tissue that makes upyour epidermis and also con-sist mainly of keratin.

Figure 18The left side of this cut apple wascoated with lemon juice. Citricacid in the lemon juice kept thesurface of the apple looking fresh.


Acids, bases, and salts in the kitchenAcids have other uses in the kitchen. Acidic marinades made ofvinegar or wine can be used to tenderize meats because they candenature proteins in the meat. That is, the acids cause the proteinmolecules to unravel and lose their characteristic shapes. As aresult, the meat becomes more tender.

Figure 19 shows that milk curdles if you add vinegar to it. Thisreaction may seem undesirable, but a similar reaction occurs inthe formation of yogurt. Bacteria convert lactose, a sugar in milk,into lactic acid. The lactic acid denatures the protein casein inmilk and changes the milk into a thick gel known as yogurt.

There are many bases and salts in the kitchen. You can uncloga drain by using the strong base sodium hydroxide, also calledlye. Baking soda, or sodium hydrogen carbonate, is a salt thatforms carbon dioxide gas at high temperatures, which makescookies rise when they are baked. Baking powder consists of bak-ing soda and an acidic substance that react to release CO2, whichmakes light, fluffy batter for cakes.

274 C H A P T E R 8


1. Describe how soap can dissolve in both oil and water. Howdoes soap work with water to remove oily dirt?

2. Explain why soap scum might form in hard water that con-tains Mg2� ions when soap is used instead of detergent towash dishes.

3. Explain why the agitation of a washing machine helps adetergent clean your clothes. (Hint: Compare this motion to rubbing your hands together when you wash them.)

4. Explain why it is not necessary for bleach to actuallyremove the substance that causes a stain.

5. Explain how milk of magnesia, an antacid, can reduce acid-ity in stomach acid.

6. List three acidic household substances and three basichousehold substances. How are the substances most often used?

7. Critical Thinking Crayon companies recommend treatingwax stains on clothes by spraying the stains with an oilylubricant, applying dishwashing liquid, and then washingthe clothes. Explain in a paragraph why this treatmentwould remove the stain.

S U M M A R Y

> Soaps and detergents candissolve in oil and water.They are usually sodium or potassium salts of car-boxylic or sulfonic acids,which have long hydrocar-bon chains.

> Detergents do not form aninsoluble scum in hardwater as soap does.

> Bleach is an alkaline solu-tion of sodium hypochlo-rite, NaOCl. Bleach is adisinfectant and oxidizesstains to a colorless form.

> Antacids are basic sub-stances that react withhydrochloric acid in thestomach.

> Acids, bases, and salts havemany practical uses in thekitchen, both in cleaningand cooking.

Figure 19Adding vinegar to milk causes themilk to curdle, because casein, themain protein in milk, becomesdenatured by the acid.


G R A P H I N G S K I L L S 275

Examine the above graph, and answer the following questions. (See Appendix A for helpinterpreting a graph.)

Does the solution’s acidity increase or decrease as calcium hydroxide is added?Explain your answer.

Identify the independent and dependent variables. What is the relationship betweenthe two variables?

At what point on the graph are there equal moles of acid and base? Explain youranswer.

Use your answer to the previous question to calculate the number of moles of acidpresent before the calcium hydroxide is added to the solution.

What is the pH of the calcium hydroxide solution added to the acid? How did youreach this conclusion?

A person who has a stomach disorder is advised to avoid acidic foods. Construct thetype of graph best suited for the data given in the table below. Which substance ismost acidic? Which substance has a pH closest to the pH of pure water?

6

5

4

3

2

1

Graphing SkillsGraphing SkillsGraphing Skills

Substance Average pH

Bananas 4.6

Dill pickles 3.4

Eggs 7.8

Salmon 6.2

Soda crackers 7.5

pH

Ca(OH)2 added (mol)0 0.2

2

4

00.4

6

8

0.80.6

10

12


8. Compared to strong acids, weak acidsa. ionize more completely in water.b. are less soluble in water. c. do not react with bases.d. ionize only slightly in water.

9. Which of the following ions could be presentin a salt?a. Br� c. H3O�

b. OH� d. H�

10. Which of the following ionic equations bestrepresents a neutralization reaction?a. Na � H2O → Na� � OH� � H2

b. HNO3 � H2O → H3O� � NO3�

c. 2OH� � NH4Cl → Cl� � H2O � NH3

d. OH� � H3O� → 2H2O

11. An increase in the hydronium ion concen-tration of a solution ________ the pH.a. raises c. does not affectb. lowers d. doubles

12. A complete neutralization of a weak acid bya strong base yields a solution that isa. basic. c. acidic.b. neutral. d. saturated.

13. Bleach removes stains bya. changing the color of the stain.b. covering the stain.c. removing the stain-causing substances.d. disinfecting the stain.

14. Which of the following is not a property ofsoap?a. It is a salt.b. It is made from petroleum.c. It dissolves in both oil and water.d. It is an ionic substance.

15. Which of the following is not an acidicmaterial found in the kitchen?a. baking soda c. vinegarb. lemon juice d. vitamin C

Chapter HighlightsBefore you begin, review the summaries ofkey ideas of each section, found at the end ofeach section. The vocabulary terms are listedon the first page of each section.

1. Which ions does an acid form in solution?a. oxygen c. hydroxideb. hydronium d. sulfur

2. Which ions does a base form in solution?a. oxygen c. hydroxideb. hydronium d. sulfur

3. A substance with a pH of 9 hasa. the same number of H3O� ions and

OH� ions.b. more H3O� ions than OH� ions.c. no H3O� ions, but many OH� ions.d. more OH� ions than H3O� ions.

4. When a solution of nitric acid is added to a solution of calcium hydroxide, the saltformed has the formulaa. Ca(NO3)2. c. H2O.b. Ca(OH)2. d. CaH.

5. An antacid relieves an overly acidic stomachbecause antacids area. acidic. c. basic.b. neutral. d. dilute.

6. Any substance that conducts electricitywhen it dissolves in water is called a(n)a. salt. c. electrolyte.b. antacid. d. weak base.

7. Detergents have replaced soap in many usesbecause detergentsa. are made from animal fat.b. do not form insoluble substances.c. are milder than soap.d. contain ammonia.

UNDERSTANDING CONCEPTSUNDERSTANDING CONCEPTS

276 C H A P T E R 8

R E V I E WC H A P T E R 8


16. Explain how the ionization of a strong aciddiffers from the ionization of a weak acid ina solution. Give an example of a strong acidand a weak acid. Show which ions formwhen each is dissolved in water.

17. Give both the name and the formula of thesalt produced in the following neutralizationreaction:

2H3O� � 2Br� � Ca2� � 2OH� → Ca2� �

2Br� � 4H2O

18. Explain how you can use the indicator litmus,in the form of litmus paper, to determinewhether a solution is acidic, basic, or neutral.

19. List the two kinds of ions that are in greatestconcentration in a solution of a strong base.

20. How is the pH of a solution related to itshydronium ion concentration? What hap-pens to pH as this concentration changes?

21. Explain how the molecular structure ofsoaps and detergents can cause water towash away oil and grease.

22. What is the active substance in bleach? Howis bleach made?

23. Why are most shampoos made from deter-gents rather than soaps?

24. Microbiologists often wipe down work areaswith a bleach solution before working withbacterial cultures. What is the purpose ofusing bleach in this way?

25. Explain why a solution of a strong acid is agood conductor of electricity.

26. What is a neutralization reaction? Howmight the product of a neutralization reaction have a pH of less than 7?

27. How would you find the concentration of astrong acid in a titration? Use the terms indi-cator and equivalence point in your answer.

28. Determining pH What is the pH of a0.001 M solution of rubidium hydroxide,RbOH, a strong base?

29. Determining pH What is the pH of a solu-tion that contains 0.10 mol of HCl in a vol-ume of 100.0 L?

30. Using pH What is the molar concentration ofhydroxide ions in a solution with a pH of 6?

31. Determining pH The concentration ofhydronium ions in a certain acid solution is100 times the concentration of hydroniumions in a second acid solution. If the secondsolution has a pH of 5, what is the pH of thefirst solution?

32. Interpreting Graphs The point at whichequal amounts of an acid and a base havereacted in a neutralization reaction is calledthe equivalence point. Study the graph of pH versus volume of base added below, and note the pH at the equivalence point.Classify both the acid and the base in thisneutralization reaction as either weak orstrong. Explain your answer.


BUILDING GR APHING SKILLSBUILDING GR APHING SKILLS

BUILDING MATH SKILLSBUILDING MATH SKILLSUSING VOC ABULARYUSING VOC ABULARY

pH

mL base added 0 25

2

4

050

6

8

100

14

75

10

12Equivalence

point


36. Problem Solving Insect bites hurt becausethe insect injects a toxin into the victim.When certain kinds of ants bite, they inject a small amount of highly irritating formicacid. Suggest a treatment that might stop an ant bite from itching or hurting.

37. Designing Systems Suppose you measurethe pH of a clear solution in a beaker andfind that it has a pH of 3. You are asked todetermine whether the solution is a verydilute solution of a strong acid or a strongersolution of a weak acid. Propose a methodto answer the question.

38. Creative Thinking You need several gramsof the substance ammonium bromide,NH4Br, for an experiment, but you do nothave any. You do, however, have a solutionof hydrobromic acid, HBr, and a solution ofammonia. Suggest a way to use an acid-basereaction to make a small quantity of NH4Br.

39. Applying Knowledge Pure water is a poorconductor of electricity. But it is still danger-ous to have any sort of plugged-in appli-ances near the bathtub or shower. Why doesthis danger exist? Explain your reasoning bydiscussing the composition of tap water.

40. Communicating Effectively When there isan oil spill in the ocean, emergency-responseteams use the properties of oil and wateralong with solubility principles to cleanspills and prevent them from spreading.Describe the research behind these tech-niques, and evaluate the impact thisresearch has had on the environment.

41. Locating Information Research the inven-tion of the pH meter by Dr. Arnold O.Beckman. Why was the pH meter invented?How does it work? Prepare a poster to pres-ent your results.

33. Interpreting Graphs The graph below showshow pH changes as a 0.1 M solution ofNaOH is added to 50 mL of a 0.1 M solutionof HCl. Use the graph to answer the follow-ing questions.

a. Describe how pH changes as the first 30 mL of NaOH solution is added. Whattakes place in the solution during thisaddition?

b. What is happening in the solution just as50 mL of NaOH has been added? Whyis the pH changing so rapidly at thispoint? (Hint: When 50 mL of the NaOHsolution has been added, equal amountsof acid and base have combined.)

c. What is happening in the solution asmore than 50 mL of NaOH solution isadded?

34. Applying Knowledge Baking soda, sodiumhydrogen carbonate (NaHCO3), is useful inthe kitchen for baking and to absorb odorsin the refrigerator. Baking soda can also betossed onto a grease fire to extinguish it.How can baking soda extinguish fires?

35. Creative Thinking If you wish to change thepH of a solution very slightly, should youadd a strong acid or a weak acid? Explainyour answer.

278 C H A P T E R 8

R E V I E WC H A P T E R 8

pH

NaOH added (mL)0 25

2

4

050

6

8

100

14

75

10

12

THINKING CR ITIC ALLYTHINKING CR ITIC ALLY

BUILDING LI FE/WORK SKILLSBUILDING LI FE/WORK SKILLS


c. f.anions

acids

cations

in waterto form

b. e.ionize dissociate

a. d.strong weak

bases

in waterto form

that are that are

42. Applying Knowledge Design an experimentto measure the pH of four types of sham-poo: baby shampoo, shampoo for extrabody, shampoo for oily hair, and shampoothat contains conditioner. Also compare twobrands of pH-balanced shampoo. Write aparagraph summarizing your results.

43. Connection to Biology The pH of humanblood is about pH 7.4 and must be keptwithin a few tenths of a pH unit of the nor-mal pH. Reactions within the human bodyensure that a proper pH is maintained. Theequilibrium shown below between carbonicacid, H2CO3, and the hydrogen carbonateion, HCO3

�, is important to maintain theblood’s pH.

H2CO3 � H2O HCO3� � H3O�

Find out what happens to keep the pH fromdecreasing as extra hydronium ions enter the blood. Also find out how the pH is keptfrom increasing as extra OH� ions enter the blood.

44. Connection to History In the 18th century,the French chemist Antoine Lavoisier experi-mented with substances containing oxygen,such as CO2 and SO2, that formed acidicsolutions when dissolved in water. His obser-vations led him to infer that for a solution tobe acidic, it must contain oxygen. Provideevidence to disprove Lavoisier’s conclusion.

45. Locating Information A reaction betweenbaking soda and a baking batter that ismade of acidic ingredients produces CO2

gas. The reaction makes the batter fluffier.Some recipes call for baking powder insteadof baking soda. Find out what regular bak-ing powder and double-acting baking pow-der are made of. How do they each differfrom baking soda?

46. Concept Mapping Copy the unfinishedconcept maps below onto a sheet of paper.Complete the maps by writing the correctword or phrase in the lettered boxes.


INTEGR ATING CONCEPTSINTEGR ATING CONCEPTS

www.scilinks.orgTopic: Baking Soda/Baking PowderSciLinks code: HK4164

→ →

Art Credits: Fig. 2A, Kristy Sprott; Fig. 3B, Kristy Sprott; Fig. 5-7, Kristy Sprott; Fig. 11, Kristy Sprott.

Photo Credits: Chapter Opener image of Weaver Ants by Philip Chapman/Taxi/Getty Images; heli-copter dropping lime by Peter Arnold, Inc.; Fig. 1, Sam Dudgeon/HRW; Fig. 2B, 3B, SergioPurtell/Foca/HRW; Fig. 4, Sam Dudgeon/HRW; Fig. 6, Charles D. Winters; Fig. 7, Charles D.Winters/Photo Researchers, Inc.; Fig. 8, Yoav Levy/Phototake; Fig. 9, Charlie Winters; Fig. 10,CNRI/Photo Researchers, Inc.; Fig. 11, Charlie Winters; Fig. 13, Frans Lanting/Minden Pictures; Fig.14, Bob Thomason/Getty Images/Stone; Fig. 15, Sam Dudgeon/HRW; Figs. 16-19, Peter VanSteen/HRW; “Skill Builder Lab,” Charlie Winters/HRW.


Measuring Quantities inan Acid-Base ReactionPreparing for Your Experiment

1. On a sheet of paper, prepare a data table similar tothe one shown at right.

� Procedure

Neutralizing HCl with NaOHSAFETY CAUTION Wear an apron or lab coat to protectyour clothing when working with chemicals. If a spill getson your clothing, rinse it off immediately with water for atleast 5 minutes, while. Wear safety goggles and gloveswhen handling chemicals. If any substance gets in youreyes, immediately flush your eyes with running water forat least 15 minutes and notify your instructor. Always usecaution when working with chemicals. Add an acid or abase to water; never do the opposite.

2. Use the marker to write “HCl” on the bulb of onepipet. This pipet should be used only for hydrochloricacid solution. Mark a second pipet NaOH. This pipetshould be used only for sodium hydroxide solution.

3. Add 40 drops of 0.1 M HCl solution to a clean testtube at a steady rate. Do not let the tip of the pipettouch the sides of the test tube. Hold the long tube of the pipet with the other hand, if necessary.

4. Add two drops of phenolphthalein indicator to thetest tube. Gently shake the test tube from side to sideto mix the liquid in the tube. Be careful not to spill orsplash the liquid.

5. Note the concentrations of the HCl and NaOH solu-tions. Predict how many drops of NaOH solution willbe required to neutralize the 40 drops of HCl. Recordyour prediction in the data table.

6. Add 25 drops of 0.1 M NaOH solution to the test tube.You will probably see a pink color develop temporarily.This is the color of phenolphthalein in a basic solution.Remember this color. Gently swirl the test tube to mixthe liquid. The pink color should disappear.

Acids and bases neutralize each other toform a salt and water. Phenolphthaleinis a good indicator to use in the neutral-ization of a strong acid by a strong base.It is a good indicator because phenol-phthalein changes color at a pH verynear the neutral point of a reaction of astrong base and a strong acid.

> Determine the volume of a basesolution needed to neutralize a givenvolume of acid solution.

> Analyze theresults to compare the volume ofbase solution needed to neutralize agiven volume of HCl solution with thevolume needed to neutralize the samevolume of H2SO4 solution.

0.1 M H2SO4 solution0.1 M HCl solution0.1 M NaOH solutionmarkerphenolphthalein indicator solutionplastic pipets, disposable test-tube racktest tubes

USING SCIENTIFIC METHODS

Objectives

Materials

Introduction

280 C H A P T E R 8 Copyright © by Holt, Rinehart and Winston. All rights reserved.

7. Add more NaOH solution to the test tube two drops at a time, and mix the liquids after each addition. As the pink color starts to disappear more slowlywhen you mix the liquids, start adding the NaOH solution one drop at a time,and mix the solution with each addition. When the mixture remains slightly pinkafter the addition of a drop and does not change within 10 seconds, you havereached the end of the neutralization reaction. Record in the data table the totalnumber of drops of NaOH solution you added.

Neutralizing H2SO4 with NaOH8. Use the marker to label a third pipet “H2SO4.” Use this pipet only for sulfuric acid

solution.

9. Repeat steps 3–6, but start with 40 drops of 0.1 M H2SO4 solution instead of40 drops of HCl solution. Make and record your prediction as in step 4.

� Analysis1. In the neutralization of HCl with NaOH, how close was

your predicted number of drops to the actual number ofdrops of NaOH solution needed? If there is a large differ-ence, explain the reasoning that led to your prediction.

2. Write a complete nonionic chemical equation for the reac-tion of HCl and NaOH. Then, write the ionic equation forthe reaction without spectator ions.

3. In the neutralization of H2SO4 with NaOH, how close wasyour predicted number of drops to the actual number ofdrops of NaOH solution needed? If there is a large differ-ence, explain the reasoning that led to your prediction.

4. Write a complete nonionic chemical equation for the reac-tion of H2SO4 and NaOH. Then, write the ionic equation forthe reaction without spectator ions.

� Conclusions5. Suppose someone tries to explain your results by saying that H2SO4 is twice as

strong an acid as HCl. How could you explain that this person’s reasoning isincorrect?


Neutralization Reaction Data

Drops NaOH Drops NaOHNumber of needed needed

drops (predicted) (measured)

HCl

H2SO4


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CHAPTER 8 Acids, Bases, and Saltsmrwelling.weebly.com/uploads/2/1/9/6/21963578/ch.8_book.pdf · Acids, Bases, and pH > Describe the ionization of strong acids in water and the dissociation