chapter 14: acids, bases, and ph - glencoe.com

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14CHAPTER

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Acids, Bases, and pHAcids, Bases, and pH14CHAPTER

14.1 Acids and Bases

Minilab 14.1 What Do Acids Do?

14.2 Strengths of Acids and Bases

MiniLab 14.2 AntacidsChemLab Household Acids

and Bases

Chapter PreviewSections Eat It or Clean With It?

Citrus fruits are a common source of acid.Because of their acidic composition,oranges and lemons are used in cleaning

solutions. Acids also may chemically react withmetal, and are a destructive force when air pollution comes in contact with marble andlimestone structures. However, citrus fruits areingested by humans on a daily basis as a com-mon source of vitamin C.

Eat It or Clean With It?

479

Testing pH Using NaturalIndicatorsHow can you use red cabbage juice to determine the relative pH of several solutions?

Safety Precautions

Materials

• small test tubes (9)• test-tube rack• concentrated red cabbage juice in a dropper bottle• labeled bottles containing: household ammonia, bak-

ing soda solution, 0.1M hydrochloric acid solution,white vinegar, colorless carbonated soft drink, boraxsoap solution, distilled water

• grease pencil

Procedure

1. Construct a data table to record your observations.2. Mark each test tube with the appropriate label.3. Half-fill each test tube with the solution to be tested.4. Add 10 drops of cabbage juice indicator to each test

tube. Gently agitate each test tube to mix the solution.5. Observe and record the color of each solution.

Analysis

Compare your observations with the table on page 504.Record in your data table the relative acid or basestrength of each solution you tested.

Scan the key terms in the chapter for new words. Try to break downeach word to find its origin, or recalla context in which you have heardthe word used before. As you read,note the words’ official definition inthe text.

Reading Chemistry

Review the following conceptsbefore studying this chapter.Chapter 5: names and formulas ofcommon acids and basesChapter 13: dissociation of ioniccompounds; hydrogen bonding

What I Already Know

Preview this chapter’s content andactivities at chemistryca.com

Start-up ActivitiesStart-up Activities

http://chemistryca.com

14.1

As you have discovered, classifying sub-stances into broad categories simplifies thestudy of chemistry. Consider some of the

chemistry classification schemes you have used.In each scheme, the categories have generallybeen opposites, such as metal versus nonmetal,ionic versus covalent, and soluble versus insoluble.The materials in each category do not share exactly thesame properties, but they share similar properties. Likewise,substances classified as acids or bases can be considered opposites. Sub-stances in each category share some general properties that make them dif-ferent from other substances. In this section, you will examine acids andbases from both a macroscopic and a submicroscopic level.

Macroscopic Properties of Acids and BasesBecause they are present in so many everyday materials, acids and

bases have been recognized as interesting substances since the time ofalchemists. Simple, observable properties distinguish the two.

It’s a Matter of Taste and FeelAlthough taste is not a safe way to classify acids and bases, you proba-

bly are familiar with the sour taste of acids. Lemon juice and vinegar, forexample, are both aqueous solutions of acids. Bases, on the other hand,taste bitter.

Bases have a slippery feel. Like taste, feel is not a safe chemical test forbases, but you are familiar with the feel of soap, a base, on the skin. Bases,such as soap, react with protein in your skin, and skin cells are removed.This reaction is part of what gives soaps a slippery feel, as well as a cleans-ing action. Figure 14.1shows how this reactionmakes some bases excel-lent drain cleaners.

SECTION

Objectives✓ Distinguish acidsfrom bases by theirproperties.

✓ Relate acids andbases to their reac-tions in water.

✓ Evaluate the centralrole of water in thechemistry of acids and bases.

Review VocabularyOsmosis: the flow ofsolvent moleculesthrough a selectivelypermeable membrane,driven by a concentra-tion difference.

New Vocabularyacidhydronium ionacidic hydrogenionizationbaseacidic anhydridebasic anhydride

SECTION PREVIEW

480 Chapter 14 Acids, Bases, and pH

Acids and Bases

Figure 14.1Bases and Protein Certain bases are excellent at dissolving hair,which is often the source of clogged drains.Hair is composed of protein.

14.1 Acids and Bases 481

Acids React with BasesAs you have learned, substances with opposite properties, such as acids

and bases, tend to react with each other. You’ll learn more about theseacid-base reactions in Chapter 15.

The reactions of acids and bases are central to the chemistry of livingsystems, the environment, and many important industrial processes. Table14.1 shows the top ten industrial chemicals produced in the United Statesin 1994. Not surprisingly, acids and bases make up half of the top ten.

Litmus Test and Other Color ChangesAcids and bases cause certain colored dyes to change color. The most

common of these dyes is litmus. When mixed with an acid, litmus is red.When added to a base, litmus is blue. Therefore, litmus is a reliable indi-cator of whether a substance is an acid or a base. Figure 14.2 shows howvegetable dyes change color in the presence of an acid or a base. Dyes suchas these are called acid-base indicators because they are often used toindicate whether substances are acids or bases.

Figure 14.2Acid-Base IndicatorsThe ability of a substance to change the colorof certain dyes is a good indication ofwhether the substance is an acid or a base.Common materials that act as acid-base indi-cators include litmus, red cabbage, radishes,tulips, and rose petals.

Chemical Billions of Pounds Acid/Base Some UsesSulfuric acid, H2SO4 78.70 Acid Car batteries; manufacture of

chemicals, fertilizer, and paperNitrogen, N2 67.54Oxygen, O2 49.67Ethylene, C2H4 48.53Lime, CaO 38.35 Base Neutralizes acidic soilsAmmonia, NH3 37.93 Base Fertilizer; cleaner; making

rayon, nylon, and nitric acidPropylene, C3H6 28.84Sodium hydroxide, NaOH 25.83 Base Drain and oven cleaners; man-

ufacture of soap and chemicalsPhosphoric acid, H3PO4 25.26 Acid Making detergents and

fertilizers; soft drinksChlorine, Cl2 24.20

Table 14.1 Top Ten Industrial Chemicals Produced in the United States in 1994

In the chemistry lab, lit-mus test paper is used.Litmus paper is madeby soaking paper in asolution of litmus andthen drying it toremove the water. Lit-mus papers are usuallyavailable in a slightlybasic form (blue) and aslightly acidic form(red).

Reactions with Metals and CarbonatesAnother characteristic property of an acid is that it reacts with metals

that are more active than hydrogen. Figure 14.3 shows how iron metalrapidly reacts with hydrochloric acid, HCl, to form iron(II) chloride,FeCl2, and hydrogen gas. However, if you were to add a piece of coppermetal to the acid, you could see that the acid will not react with coppermetal. This property explains why acids corrode most metals. Bases donot commonly react with metals.

Another simple test that distinguishes acids from bases is the reactionof acids with ionic compounds that contain the carbonate ion, CO3

2�, toform carbon dioxide gas, water, and another compound, as shown in Fig-ure 14.3. A similar reaction, also shown in Figure 14.3, is the source of thedestructive action of acidic pollution on marble and limestone sculptures.Bases do not react with carbonates.

What do acids do?Most acids tend to be reactive substances. Test the reac-

tivities of three acids with several common substances,and develop an operational definition for acidic solutions.

Procedure

1. Wear an apron and goggles.

2. Use a labeled microtip pipet toadd 10 drops of 3M hydrochlo-ric acid, HCl, to wells D1-D6 ofa clean, 24-well microplate. Inthe same manner, add 10 dropsof 3M sulfuric acid, H2SO4, towells C1-C6 and 10 drops of3M acetic acid, HC2H3O2, towells B1-B6.

3. Dip blue litmus paper into thesolutions in wells D1, C1, andB1. Record your observations.

4. Add 2 drops of bromothymolblue indicator solution to wellsD2, C2, and B2. This indicatorturns from blue to yellow as thesolutions become more acidic.Record your observations.

5. In a similar manner, add mar-ble chips (calcium carbonate)to wells D3, C3, and B3; pieces

of zinc to wells D4, C4, and B4;pieces of aluminum to wellsD5, C5, and B5; and a smallamount of egg white to wellsD6, C6, and B6. Record yourobservations.

6. Dispose of all materials asdirected by your teacher. Rinsethe microplate with tap water,then distilled water.

Analysis1. Summarize the reactions of the

three acids with the substancesyou tested. This summary con-stitutes an operational defini-tion of an acid.

2. Which acid, although it had thesame molar concentration asthe other acids, reacted lessnoticeably? Explain thisbehavior.

1


Except for Group I car-bonates, carbonate-containing compoundsare almost completelyinsoluble in water. Thismakes naturally occur-ring substances such asmarble and limestonestable materials forsculpting and building.

SMALLSCALESMALLSCALE

Defining Acids and Bases—A Submicroscopic Look

The description of acids and bases in terms of their physical and chem-ical properties is useful for classification purposes. However, to under-stand these properties, you need to know about the behavior of acids andbases at the submicroscopic level.

Submicroscopic Behavior of AcidsThe submicroscopic behavior of acids when they dissolve in water can be

described in several ways. The simplest definition is that an acid is a sub-stance that produces hydronium ions when it dissolves in water. A hydroni-um ion, H3O

�, consists of a hydrogen ion attached to a water molecule.

Figure 14.3Acids with Metals and CarbonatesTypical behavior in certain chemical reactions helps identifysubstances as acids.

� Vinegar, a solution of acetic acid, reactswith egg shell, which is primarily calci-um carbonate, to produce carbon diox-ide, calcium acetate, and water.

2HC2H3O2(aq) � CaCO3(s) ˇCO2(g) � Ca(C2H3O2)2(aq) � H2O(l)

Calcium carbonate is the majorcomponent in limestone and mar-ble. In the presence of acids in theenvironment, marble and lime-stone sculptures and buildings canbe damaged or destroyed. �

lithiumpotassiumcalciumsodiummagnesiumaluminumzincchromiumironnickeltinleadhydrogencoppermercurysilverplatinumgold

Dec

reas

ing

activ

ity


� Acids react with metals that are more activethan hydrogen to form both a compound ofthe metal and hydrogen gas.

Fe(s) � 2HCl(aq) ˇ FeCl2(aq) � H2(g)

&TECHNOLOGYC H E M I S T R Y

Manufacturing Sulfuric AcidYou might not expect that a simple acid would

acquire worldwide status, but sulfuric acid has donejust that. Most industrialized nations produce signif-icant quantities of the chemical. The United Statesalone produces 40 million tons of sulfuric acid everyyear.

With such quantities being produced, this productmust have many uses. Ninety percent of the sulfuricacid made in the United States is used in the produc-tion of liquid fertilizers and other inorganic chemi-cals. The rest is used in refining petroleum, in steelproduction, and in producing organic chemicals.Sulfuric acid is also useful in removing unwantedmaterials from ores.

The Manufacturing Process The production of sulfuric acid is fairly simple.

It starts with burning sulfur to produce sulfurdioxide.

S(s) � O2(g) ˇ SO2(g)


1. Hypothesizing Why do you suppose sulfurtrioxide is bubbled through a solution of sul-furic acid instead of through water to producesulfuric acid? Isn’t this inefficient?

2. Inferring Some people use the quantity ofsulfuric acid produced by an industrializednation as an economic indicator. Why is sulfu-ric acid production useful in this regard?

DISCUSSING THE TECHNOLOGY

The next step in the process is called the contactmethod because the sulfur dioxide and oxygenmolecules are in contact with a catalyst, usuallyvanadium pentoxide, V2O5. When the sulfurdioxide and oxygen gases pass through a heatedtube that contains layers of the pellet-size cata-lyst, the sulfur dioxide is converted to sulfur tri-oxide. To make sure the reaction is complete,contact with the catalyst takes place twice.

catalyst

2SO2(g) � O2(g) ˇ 2SO3(g)

Then the sulfur trioxide is bubbled through asolution of sulfuric acid to produce pyrosulfuricacid, H2S2O7. Pyrosulfuric acid is then added towater to produce sulfuric acid.

SO3(g) � H2SO4(l) ˇ H2S2O7(l)

H2S2O7(l) � H2O(l) ˇ 2H2SO4(l)


For example, hydrochloric acid is produced by dissolving hydrogenchloride gas, HCl, in water. Remember from Chapter 13 that water is apolar molecule that is able to form strong hydrogen bonds with solutesthat also form hydrogen bonds. When HCl dissolves in water, it produceshydronium ions by the reaction shown below. HCl is definitely an acid; itproduces H3O

� when dissolved in water.

HCl(g) � H2O(l) ˇ H3O�(aq) � Cl�(aq)

Acetic acid, HC2H3O2, undergoes a similar reaction when it dissolves inwater to form a vinegar solution.

HC2H3O2(aq) � H2O(l) ˇ H3O�(aq) � C2H3O2

�(aq)

Notice the similarities in these two reactions. In both cases, the dissolvedsubstance reacts with water to form hydronium ions and a negativelycharged ion.

Acidic Hydrogen AtomsHow and why are hydronium ions formed? At the submicroscopic level,

the reaction of an acid with water is a transfer of a hydrogen ion, H�, froman acid to a water molecule. This transfer forms the positively chargedhydronium ion, H3O

�, and a negatively charged ion. In an acid, any hydro-gen atom that can be transferred to water is called an acidic hydrogen.

Take another look at the acetic acid example. Although a molecule ofacetic acid, HC2H3O2, contains four hydrogen atoms, only one is an acidichydrogen that participates in the transfer. The other hydrogen atomsremain a part of the acetate ion. Figure 14.4 shows that it is possible foracids to have more than one acidic hydrogen per molecule.

To help distinguish acids from other hydrogen-containing molecules,acidic hydrogens are written first in the formula. Any time hydrogen is thefirst element in a formula of a compound, the substance is an acid.

H SOSulfuric acid

a diprotic acid

2 4 H C H OCitric acid

a triprotic acid

3 6 5 7

HC H OAcetic acid

2 HClHydrochloric acid

3 2

Monoprotic acids

Figure 14.4Acidic HydrogenIf a hydrogen atom loses its electron, allthat remains is a proton. Prefixes, usedwith the term protic, which refers to theremaining proton, indicate how manyacidic hydrogens are present in an acid.

� All acids that have more than oneacidic hydrogen per molecule arecalled polyprotic acids. Polyproticacids with two acidic hydrogens arediprotic acids. Those with threeacidic hydrogens are triprotic acids.

� Acids such as acetic acid, HC2H3O2,and hydrochloric acid, HCl, are calledmonoprotic acids. Monoprotic acidscontain only one acidic hydrogen.

acid:acidus (L) sour

One property ofacids is that theytaste sour.


Chemical Reaction ShorthandYou know that you can write an equation for the ionization of a specif-

ic acid. However, it is sometimes handy to represent the formation ofhydronium ions when acids dissolve in water by a general equation. Inthis general equation, any monoprotic acid is represented by the generalformula HA. Compare this general equation to the specific equation forthe ionization of HCl.

HCl(g) � H2O(l) ˇ H3O�(aq) � Cl�(aq)

HA � H2O(l) ˇ H3O�(aq) � A�(aq)

Although the form of the general equation written above is the mostcomplete, it is more convenient to use a shorthand form of the reaction.In the shorthand form, water is not shown as participating in the reac-tion, and the hydronium ion is represented as an aqueous hydrogen ion.

HA(aq) ˇ H�(aq) � A�(aq)

Similar equations apply to the transfer of hydrogen ions from polyproticacids, such as sulfuric acid, which is used in Figure 14.5. Equationsdepicting the transfer are shown in Figure 14.6.

When using this convenient shorthand style, keep in mind that thewater molecule is always an active participant in the reaction, even thoughit is not written in the equation.

Figure 14.6Ionization of Poly-protic AcidsPolyprotic acids losetheir acidic hydrogensone at a time. For adiprotic acid, there aretwo steps (A). Fortriprotic acids, thereare three steps (B).

Figure 14.5Steel-MakingSulfuric acid, which is used tomake steel, is an example of adiprotic acid.

A General:H A(aq) ˇ H (aq) � HA (aq)HA (aq) ˇ H (aq) � A (aq)

B H A(aq) ˇ H (aq) � H A (aq)H A (aq)ˇ H (aq) � HA (aq)HA (aq)ˇ H (aq) � A (aq)

Example:H SO (aq) ˇ H (aq) � HSO (aq)HSO (aq) ˇ H (aq) � SO

H PO (aq) ˇ H (aq) � H PO (aq)H PO (aq)ˇ H (aq) � HPO (aq)HPO (aq)ˇ H (aq) � PO (aq)

2 2 4 4

2 2

2 23 3

� �

�

�

�

�

�

�

�

��

�

�

� �

4 4�

4

4 4

4

4

�

�

2– 2–

2–

2– 2–

42–3– 3–


BIOLOGY CONNECTION

Connecting to Chemistry

1. Hypothesizing In aheart attack, bloodflow to some partsof the heart may bestopped or greatlyreduced. Howmight this affect theacid-base relation-ship in blood in theheart muscle?

2. Applying Bloodgases may fail toshow major abnor-malities while thepatient is at rest.Suggest a way toovercome this prob-lem if the patient isnot bedridden.

consider case histories. In one case, after apneumonia patient was put on a respirator,she failed to improve. Her blood test showedthe following.

PCO2 17 mm Hg HCO3� 18 m Eq/liter

PO2 75 mm Hg pH 7.65

The low carbon dioxide level and the high pHwhile on the respirator were unexpected.These levels led the physician to check thesettings on the respirator. The volume adjust-ment on the respirator had slipped. Thepatient was receiving twice the recommendedquantity of air. This caused respiratory alka-losis, a condition of decreased acidity of theblood and tissues. When the respirator wasadjusted, the blood levels returned to normalas the acid-base balance was reestablished,and the patient began to recover.

Measurement of Blood Gases

There are only four hydrogen ionsin blood for every 100 000 000 otherions and molecules in blood. Butenzyme reactions in the body aresensitive to small changes in the con-centration of hydrogen ions, so it iscrucial. Hydrogen ions affect acid-base relationships in body fluids.

Plasma Component Normal RangeHCO3

� 23–29 m Eq/liter*Pco2 35–45 mm HgPo2 75–100 mm HgpH 7.35–7.45*expressed in molar equivalents per liter

Normal Ranges of Some Blood Components

Interpreting acid-base status in bloodWhen a patient is ill, the doctor’s role is todiagnose the patient’s condition. Sometimes,this is difficult because different conditionsmay have similar symptoms. One helpful toolthat the physician has is a blood test thatprovides information about the acid-baserelationships in blood. This particular bloodtest will provide data on acidity (pH), pres-sure caused by dissolved carbon dioxide(PCO2), pressure caused by dissolved oxygen(PO2), and hydrogen carbonate concentration(HCO3

�). The normal ranges of these com-ponents are shown in the table above.

Case histories To see how a physician usesacid-base relationships, it is interesting to


Acid IonizationIn the reaction of an acid with water, ions are formed from a covalent

compound. When ions form from a covalent compound, the process iscalled ionization. Specifically, acids form ions in a process called acid ion-ization.

Acids Are ElectrolytesBecause acids ionize to form ions in water, acidic solutions conduct elec-tricity. As you learned in Chapter 4, substances that dissolve in water toform conducting solutions are called electrolytes. Figure 14.7 comparesthe electrical conductivities of water, a solution of an ionic compound,and a solution of a weak acid.

Figure 14.7ConductivityThe electrical conductivities ofsolutions are easy to compareby using a simple circuit. Thebrightness of the light indi-cates the relative electricalconductivity of the solutions.

� Distilled water is nonconducting. � 1M NaCl isan excellentconductor.

� 1M HC2H3O2 is a weak conductor.

As opposed to solutions of ionic compounds (such as table salt), whichare always excellent conductors of electricity, acidic solutions have electri-cal conductivities ranging from strong to weak. The range of electricalconductivities exhibited by different acidic solutions distinguishes acidionization from ionic dissociation. The range also indicates that acids varyin their ability to produce ions.

Submicroscopic Behavior of BasesThe behavior of bases is also described at the molecular level by the

interaction of the base with water. A base is a substance that produceshydroxide ions, OH�, when it dissolves in water. There are two mecha-nisms by which bases produce hydroxide ions when they dissolve in water.


Reversing the Transfer: Bases That Accept H�

A few bases are covalent compounds that produce hydroxide ions by anionization process when dissolved in water. The ionization involves thetransfer of a hydrogen ion from water to the base. The most commonexample of this type of base is ammonia, NH3.

When ammonia gas dissolves in water, some of the aqueous ammoniamolecules react with water molecules to form ammonium ions andhydroxide ions, as shown in this reaction.

NH3(g) � H2O(l) NH4�(aq) � OH�(aq)

Ammonia is a base. It produces hydroxide ions in water, but by a differentmechanism than that in the NaOH example. In the reaction with ammo-nia, the water molecule is an active chemical reactant. Water moleculestransfer hydrogen ions to ammonia molecules.

It is also helpful to have a general reaction for the ionization of a cova-lent base, which is represented by the letter B. Study the equation for thegeneral reaction.

B � H2O(l) BH�(aq) � OH�(aq)Ø

Ø

Figure 14.8Dissociation of Some Metal HydroxidesAll of these compounds are bases becausethey produce hydroxide ions when theydissolve in water.

Simple Bases: Metal HydroxidesThe simplest kind of base is a water-soluble ionic compound, such as

sodium hydroxide, that contains the hydroxide ion as the negative ion.When NaOH dissolves in water, for example, it dissociates into aqueoussodium ions and hydroxide ions, as shown below.

H2O

NaOH(s) ˇ Na�(aq) � OH�(aq)

NaOH is definitely a base because it produces hydroxide ions when it dis-solves in water. You can predict that any water-soluble or slightly water-soluble metal hydroxide will be a base when added to water.

Water plays a different role here than in the formation of hydroniumions when acids ionize in water. Water molecules do not chemically reactwith this type of base. The hydroxide ion is formed by simple ionic disso-ciation, and no transfer occurs between the base and the water moleculesto form the hydroxide ions.

Just as a polyprotic acid in water produces more than one hydroniumion, it is possible for a formula unit of a metal hydroxide to produce morethan one hydroxide ion. Calcium hydroxide, Ca(OH)2, and aluminumhydroxide, Al(OH)3, are examples of such bases, as shown in Figure 14.8.

On the JobMs. Tayag, what do you do on your job?

I’m in the Research and DevelopmentDepartment of a cosmetic laboratory. Iformulate cosmetics, such as shampoos,

lotions, and bubble baths, for cosmeticcompanies.

Can you give us an idea of a typical for-mula for a shampoo?

A simple shampoo consists of a mixture ofwater, sodium lauryl sulfate, and an amideto make it foam. I heat the mixture and

then I have to adjust the acidity. Most shampoosare neutral. If it’s more basic than that, I adjust itwith a citric acid solution. Then I cool it and checkthe viscosity, or how it flows. I don’t want it to beeither water-thin or molasses-thick, so I’ll adjustthe viscosity by using a 20 percent sodium chlo-ride solution. Perfume and color are added tomake it smell and look good.

The label on a cosmetic usually lists wateras the first ingredient. Does that mean it’smostly water?

Yes. Face creams have the lowest amountof water, about 60 percent. The amount ofwater used depends on the skin type.

What colorings do you add to the cosmet-ics you make?

I use colors approved by the Food andDrug Administration. They come in basiccolors, but I can combine them to produce

other colors. Green is the most popular coloringfor shampoo. That color seems to be associatedwith freshness and cleanliness.

What trends do you see developing incosmetics?

There are more cosmetics created especial-ly for different ethnic groups. Sunscreen isbeing added to more and more cosmetics as people become increasingly aware of the

Meet Fe Tayag, Cosmetic Bench Chemist

It pays to be a careful reader of labels. Here’s a hintfrom Ms. Tayag, who has formulated cosmetics for morethan 20 years. Many cosmetic companies find it is a goodselling point to add sunscreen to their products. But unlessthe container specifies an SPF (sun protection factor) as anumber, there probably isn’t enough sunscreen to domuch good. In this interview, Ms. Tayag shares other cos-metics savvy that can make you a wiser shopper.


damage that ultraviolet light can do to the skin.And, because a large part of the population is get-ting older, ingredients that are supposed to delaythe aging effects, such as antioxidants, are becom-ing more popular. In addition, there’s lots of inter-est in antiallergenic, natural cosmetics that areboth unscented and uncolored.

Early InfluencesHow did you get interested in becoming achemist?

My father was a warehouse man for a cos-metics company in the Philippines, where Igrew up. He was fascinated by the process

of producing cosmetics. Because he thought thejob of a chemist was a very dignified one, heencouraged me to study chemistry. Our family,which included eight children, was poor, but hesomehow found a way to send me to college.

Did you enjoy the study of chemistry incollege?

Not at first. I had a tough time in collegeand kept asking myself, “Why did I take thiscourse?” I cried at exam time, but I couldn’t

bear to disappoint my father. I prayed a lot, and Ithought of my father struggling to find money topay my tuition. That helped me find the courage tocontinue. My third year of college marked a turningpoint, and my studies became easier for me.

Were there people besides your fatherwho influenced you in your career?

A friend of my father helped me get a job inthe cosmetics lab while I was still in school. Iworked days and attended school at nights.

That way, I got to see what chemistry was all aboutin the real world. I felt I was ahead of students wholacked practical experience. For instance, in my col-loid chemistry class, I brought materials to schooland demonstrated how to make a cleansing cream.

Personal InsightsDo you consider chemistry to be a littlelike cooking?

Yes. When I cook, I rely heavily on mysenses of sight and smell. In my opinion, akeen sense of smell and a good ability to

make observations are very important for achemist, too.

Some people think that cosmetics arefrivolous. Do you agree?

No. I think it’s important for people’s self-confidence to look nice. Because peoplewant to remain attractive and young-looking, this is an industry that will never die out.


These career opportunities are related to cos-metic chemistry.

Food and Drug Inspector College degree pluswritten examinationsManufacturers’ Sales Representative Highschool diplomaCosmetologist State-administered exam

CAREER CONNECTION


Figure 14.9Bases as ElectrolytesThe electrical conductivity of1M NaOH is greater than thatof 1M NH3. These differencesshow that aqueous solutionsof bases may be strong orweak electrolytes, based onwhether many or few ions arein solution.

Bases Are ElectrolytesBecause a base in water produces ions, you can predict that aqueous

solutions of bases will conduct electricity. Figure 14.9 compares the con-ductivity of a 1M NaOH solution with that of a 1M NH3 solution. As withacids, the ability of basic solutions to conduct electricity varies, dependingupon the base. This variability is evidence that differences exist in theability of different bases to produce ions.

Why does water transfer H� to bases?Think back to why acids transfer hydrogen ions to water. The same

model can be used to explain why water molecules lose hydrogen ions tocovalent bases when they dissolve in water. Consider the example ofammonia. Ammonia is a polar molecule because it contains polar cova-lent N—H bonds. The nitrogen end of the molecule has a slight negativecharge, and the hydrogen atoms each have a slight positive charge. A lonepair of electrons is also on the central nitrogen. Look at Figure 14.10 tosee what happens when polar ammonia molecules dissolve in polar watermolecules.

Other Acids and Bases: AnhydridesTwo related classes of compounds do not fit the previous models of

acids and bases, but they still act as acids or bases. These compounds areboth oxides, which are compounds containing oxygen bonded to just oneother element. These oxides are called anhydrides, which means that theycontain no water.

Anhydrides differ, depending upon whether the oxygen is bonded to ametal or a nonmetal. Nonmetal oxides form acids when they react withwater and are called acidic anhydrides. Metal oxides, on the other hand,react with water to form bases and are called basic anhydrides. In both ofthese reactions, water is an active reactant. Now, examine some examplesof anhydrides.

H

HO

H

O

H H

N

�

� �

�H H

H

H H

N


Acidic Anhydrides and Acid RainProbably the most familiar acidic anhydride is carbon dioxide, CO2.

Water that has had carbon dioxide bubbled through it turns blue litmusto red, indicating that CO2 and water form an acid, carbonic acid, H2CO3.A solution of CO2 also has a slightly sour taste, which is one of the rea-sons that carbonated water is such a refreshing beverage.

Carbon dioxide is a minor component in Earth’s atmosphere and animportant component in the carbon cycle. Because CO2 is always in theatmosphere, when it rains, CO2 dissolves in rainwater, forming carbonicacid, H2CO3. The result is that rain is always slightly acidic. If rain is alwaysacidic, why is increased acidity in rain such an environmental concern?

The acidity of normal rain does not damage the environment. However,other nonmetal oxides such as sulfur oxides are sometimes present in theatmosphere. Also, levels of carbon dioxide are sometimes higher than normal.

The major source of sulfur oxides in the atmosphere is the burning ofsulfur-containing coal in power plants. As this type of coal burns in afurnace, sulfur dioxide gas, SO2, is produced. The SO2 escapes into theatmosphere, where it reacts with more oxygen to form sulfur trioxide, SO3.

Figure 14.10Forming Ammonium and Hydroxide IonsBecause an aqueous solution of ammonia contains ammoniumions and hydroxide ions, such a solution is commonly referred toas ammonium hydroxide.

NH

HH NH

HHHO

HH O

H

� �

A Ammonia has atrigonal pyramidgeometry and is apolar molecule.

B The hydrogen bond that formsbetween the N end of NH3 and the Hend of H2O is strong enough to pull anH� completely away from H2O. The twoelectrons in the broken O—H bondremain as a lone pair on the O. Theresult is a stable hydroxide ion, OH�.

C The H� bonds to the N in NH3,using the lone pair of elec-trons on the N to form afourth N—H bond and a sta-ble ammonium ion, NH4

�.

D The electron dotstructures showthat these ionsare stable. Eachatom in the dotstructures has astable numberof valence elec-trons.


At room temperature, the reaction between nitrogen, N2, and O2

is slow and insignificant. At the high temperatures in an automobileengine, the reaction between N2 and O2 goes quickly, and largeamounts of nitrogen oxides are produced in exhaust, Figure 14.11.

When sulfur oxides, nitrogen oxides, and increased amounts ofcarbon dioxide dissolve in rain, they undergo acid-forming reac-tions and produce what is commonly referred to as acid rain.

Examples: SO2(g) � H2O(l) ˇ H2SO3(aq)SO3(g) � H2O(l) ˇ H2SO4(aq)

2NO2(g) � H2O(l) ˇ HNO3(aq) � HNO2(aq)CO2(g) � H2O(l) ˇ H2CO3(aq)

Acid rain has been significantly reduced over the past decade as newmechanisms for trapping nonmetal oxides before they get into theatmosphere have been developed. Read the Chemistry and Societyfeature for more information about this type of air pollution.

Basic Anhydrides and Making Your Garden GrowUnlike nonmetal oxides, which are covalent compounds, metal oxides

are ionic compounds. When metal oxides react with water, they producehydroxide ions.

Gardeners sometimes use lime to treat their soil, as shown in Figure14.12. Lime is the common name for the chemical compound calciumoxide, CaO. When CaO is spread on soil, it reacts with water in the soil toform calcium hydroxide, Ca(OH)2. This compound then forms calciumand hydroxide ions.

CaO(s) � H2O(l) ˇ Ca(OH)2(aq)Ca(OH)2(aq) ˇ Ca2�(aq) � 2OH�(aq)

A similar reaction was used historically to produce an important com-modity, soap. Early soap makers used the basic properties of metal oxides.When wood burns, the metal atoms in the wood form solid metal oxidesin the burning process.These metal oxides are pre-dominantly those of sodium,potassium, and calcium.These metal oxides are ionicso they are solids, even at thehigh temperature of a roar-ing fire. They are the majorcomponent of the ash that isleft when the fire burns out.

Figure 14.11Nitrogen OxidesThe major source of nitrogenoxides in the atmosphere isautomobiles.

Figure 14.12Making Soil More BasicAdding lime to soil makes the soil less acidic andmore favorable for growing many types of plants.Because Ca(OH)2 is only slightly water soluble, itprovides a longer-lasting source of base than pro-vided by more soluble ionic hydroxides.


Atmospheric PollutionThe air you breathe is literally a matter of life

and death. Atmospheric oxygen is taken into yourbody and, during respiration, reacts with glucoseto produce the energy required for all the lifeprocesses that keep you going.

Unfortunately, the same air, at times, may con-tain materials that cause respiratory diseases andbring about other harmful effects. Air is often pol-luted with chemicals produced by human activity.Even Earth itself coughs up some of the same airpollutants during volcanic eruptions.

Introducing the major air pollutants The majorchemicals that pollute the air are carbon monoxide,CO; carbon dioxide, CO2; sulfur dioxide, SO2;nitrogen monoxide, NO; nitrogen dioxide, NO2;hydrocarbons; and suspended particles.

In addition, pollutants form under the influenceof sunlight when oxygen, nitrogen oxides, andhydrocarbons react. These reactions produce ozone,O3, and aldehydes such as formaldehyde, CH2O.Why are pollutants a problem?

Acid rain What do the salmon and the pine treesin the photos have in common? Both have suc-cumbed to the acid environment in which they live.They are two of the many victims of acid rain.

Unpolluted rain is not harmful. However, manyindustrial and power plants burn coal and oil. Thesmoke produced may contain large quantities of sul-fur oxides, suspended particles, and nitrogen oxides.Automobiles also contribute to the problem by emit-ting similar oxides. These chemicals react with waterin the air to form acids, such as sulfuric acid. Theseacids reach the surface of Earth in fog, rain, snow,and dew. Acid rain can have a disastrous effect whenit reaches bodies ofwater and water-ways. But if a lakehas a high limestonecontent, it is able tosomewhat neutralizethe acid.

Smog Large cities with many automobiles mayhave another problem with airborne pollutants. Itis called smog, which is a haze or fog that is madeharmful by the chemical fumes and suspendedparticles it contains.

A type of smog known as photochemical smogfrequently occurs in large cities in sunny, dry cli-mates. When the pollutants from automobileexhaust enter the air and are exposed to sunlight,they interact to produce photochemical smog. Thistype of smog is generally worse on hot days andbetween 11 A.M. and 4 P.M. when exhaust has accu-mulated in the air.

Chemistry and

1. Acquiring Information Research free trade inthis country. How might the issue of free tradeinfluence the problems of air pollution in thiscountry?

2. Thinking Critically Older-model cars areresponsible for the greatest amount of air pollu-tants being vented into the atmosphere. Hold adebate on whether these cars should be ban-ished from the highways.

Analyzing the Issue


This early soap-makingprocess is shown in Figure14.13. The reaction of waterand sodium oxide, Na2O, oneof the metal oxides in woodash, is similar to that shown forlime and water.

Na2O(s) � H2O(l) ˇ2NaOH(aq)

NaOH(aq) ˇNa�(aq) � OH�(aq)

The Macroscopic-Submicroscopic Acid-Base Connection

As you have discovered, the properties of acids and bases are determinedby the submicroscopic interactions between the acid or base and the sol-vent water. For example, HCl and HC2H3O2 both interact with water tocause a transfer of hydrogen ions from the acid to water molecules to formhydronium ions. Both solutions turn blue litmus red. Even though theseproperties are the same for both acids, remember that the conductivity of a1M HCl solution is much greater than that of a 1M HC2H3O2 solution.

A base interacts with water molecules to form hydroxide ions either byionic dissociation or by the transfer of a hydrogen ion from a water mole-cule to the base. Consider a 1M NaOH solution and a 1M NH3 solution.Both solutions are basic. They each turn red litmus to blue. But the NaOHsolution shows strong electrical conductivity, while the NH3 solution isonly weakly conducting.

Why do different acids have some properties in common and yet differin other properties? Why is the same thing true for bases? Section 14.2will explain these differences.

Understanding Concepts1. Make a table that compares and contrasts the

properties of acids and bases.

2. Use a chemical equation to show how aqueousHNO3 fits the definition of an acid.

3. Consider the oxides MgO and CO2. For eachoxide, tell whether it is a basic anhydride or anacidic anhydride. Write an equation for each todemonstrate its acid-base chemistry.

Thinking Critically4. Applying Concepts Chemists often call a

hydrogen ion a proton. Explain why an acid issometimes called a proton donor, and a base issometimes called a proton acceptor.

Applying Chemistry5. Using Soap After using soap to wash dishes by

hand, it is sometimes difficult to keep yourhands from remaining slick. Explain why rins-ing your hands in lemon juice would makethem less slick.

SECTION REVIEW

Figure 14.13Making SoapLye was produced by collect-ing wood ashes and soakingthem in water. After severaldays, the highly basic solutionwas separated from the undis-solved ash and combined withanimal fat. The lye reactedwith the fat to make soap.

For more practice with solvingproblems, see SupplementalPractice Problems,Appendix B.

chemistryca.com/self_check_quiz

http://chemistryca.com/self_check_quiz

14.2

From reading Section 14.1, you know that all acids have a sour taste, butthey may differ in how readily they react with another substance. Youwouldn’t hesitate to use the acetic acid in vinegar on a salad, but you

certainly wouldn’t use hydrochloric acid, which may beused to clean brick, on any typeof food. All bases also sharesome properties but differ inothers. You would readily use adilute ammonia solution as acleaner, but you certainlywouldn’t let sodium hydroxide,which is used in drain cleaners,come in contact with your skin.These two bases differ greatly inhow they react.

Strong Acids and BasesWhat’s going on? You know that when acids and bases are mixed with

water, they form ions. Much of the behavior of acids and bases dependson how many ions are formed by a particular acid or base in water. Thedegree to which bases and acids produce ions depends on the nature ofthe acid or base.

Acids and bases are classified into one of two categories dependingupon their strength, which is the degree to which they form ions. Thestrong category is reserved for those substances, such as NaOH and HCl,that completely dissociate or ionize and produce the maximum numberof ions when dissolved in water. All other acids and bases are classified asweak because they produce few ions when dissolved in water.

Strong BasesSodium hydroxide, NaOH, is a strong base because when NaOH dis-

solves in water, all NaOH formula units dissociate into separate sodiumand hydroxide ions. The dissociation of the base is complete. The strengthof a base is based on the percent of units dissociated, not the number ofOH� ions produced. Some bases, such as Mg(OH)2, are not very solublein water, and they don’t produce a large number of OH� ions. However,they are still considered to be strong bases because all of the base thatdoes dissolve completely dissociates.

Strengths of Acids and Bases

SECTION

14.2 Strengths of Acids and Bases 497

Objectives✓ Relate differentelectrical conductivi-ties of acidic and basicsolutions to theirdegree of dissociationor ionization.

✓ Distinguish strongand weak acids orbases by their degreeof dissociation orionization.

✓ Compare and con-trast the compositionof strong and weaksolutions of acids orbases.

✓ Relate pH to thestrengths of acids andbases.

Review VocabularyIonization: theprocess in which ionsform from a covalentcompound.

New Vocabularystrong basestrong acidweak acidweak basepH

SECTION PREVIEW


Strong Acids Strong BasesPerchloric acid, HClO4 Lithium hydroxide, LiOHSulfuric acid, H2SO4 Sodium hydroxide, NaOHHydriodic acid, HI Potassium hydroxide, KOHHydrobromic acid, HBr Calcium hydroxide, Ca(OH)2

Hydrochloric acid, HCl Strontium hydroxide, Sr(OH)2

Nitric acid, HNO3 Barium hydroxide, Ba(OH)2

Magnesium hydroxide, Mg(OH)2

Table 14.2 Common Strong Acids and Bases

The strong bases shown in Table 14.2 are all ionic compounds that con-tain hydroxide ions. NaOH and KOH are the most common strong basesyou will encounter. A 1M solution of NaOH and a 1M solution of KOH willeach contain 1M OH� because both compounds completely dissociate.

Strong AcidsHCl is a strong acid because no HCl molecules are in a water solution

of HCl. Because of the strong attraction between the water molecules andHCl molecules, every HCl molecule ionizes. A 1M HCl solution contains1M H3O

� and 1M Cl�. Similarly, a 1M HNO3 solution contains 1M H3O�

and 1M NO3�. As before, the labeling of a solution as 1M HNO3 is not

particularly descriptive of the submicroscopic composition of the solution.Table 14.2 lists common

strong acids and bases.Because they are used so often,it is helpful to memorize theirnames and formulas. They allcompletely dissociate or ionizeinto ions when they dissolve inwater. If an acid or base is notlisted in this group, it is con-sidered to be a weak acid orbase. However, the termsstrong and weak are notabsolute. Strength of acids andbases covers a wide range fromextremely strong to extremelyweak. Notice that the strongestbases are all hydroxides ofGroup I, the alkali metals, andGroup II, the alkaline earthmetals. Alkali is a term fre-quently used to refer to mate-rials that have noticeably basicproperties.

H

HCH3

C

CH2OH

O

C

O

O

C

C

O

O

HO

H

C

H

C

C C

C C

O

H H

C C

H O

CH

H

H

H O

C

O H

OH

HCHO2

H2C6H6O6

HC7H5O2

HC2H3O2

Formic

Ascorbic(vitamin C)

Benzoic

Acetic

Incr

easi

ng

Stre

ngt

h

Figure 14.14Some Common Weak AcidsSome common weak acidsvary in their structures.


Weak Acids and BasesThe weak category of acids and bases contains those with a wide range

of strengths. This is the category into which most acids and bases fall.Instead of being completely ionized, weak acids and bases are only partial-ly ionized.

Weak AcidsAcetic acid, HC2H3O2, is a good example of a weak acid. In a 1M

HC2H3O2 solution, less than 0.5 percent of the acetic acid molecules ion-ize, and 99.5 percent of the acetic acid molecules remain as molecules.Another way to think of this is to consider 1000 acetic acid molecules in awater solution. On the average, only five of the 1000 molecules transfertheir single hydrogen ion to a water molecule. The molarity of hydroniumion produced in a 1M HC2H3O2 solution is much less than 1M due to thispartial ionization. Other common weak acids include phosphoric acid,H3PO4, and carbonic acid, both of which are found in soft drinks.

The molecular structure of a weak acid determines the extent to whichthe acid ionizes in water. Figure 14.14 shows the variety of structures ofsome common weak acids.

Figure 14.15 uses a graph format to show the dramatic difference indegree of ionization between a solution of a weak acid and one of a strongacid. A solution of weak acid contains a mixture of un-ionized acid mole-cules, hydronium ions, and the corresponding negative ions. The concentra-tion of the un-ionized acid is always the greatest of the three concentrations.

Figure 14.15Strong and Weak AcidsThe composition of an acidic solutiondepends upon the strength of the acid.

Concentration beforeionization

Equilibrium concentrationsafter ionization

Strong acid, such as

HCl

100%

ionization

Partial

ionization

0%

ionization

Weak acid,such asHCHO

Very weak acid,such asHC H O

HA

HA HA

HA HA

H O A

2

2 3 2

3+ –

H O A3+ –

ˇ

ˇ

ˇ

�

�


Weak BasesAmmonia is a weak base because most of its molecules don’t react with

water to form ions. In a 1M aqueous solution of ammonia, only about 0.5 percent of the ammonia molecules react with water to form ammoni-um and hydroxide ions. About 99.5 percent of the ammonia moleculesremain as intact molecules. The molarity of hydroxide ions in a 1Mammonia solution is much less than 1M. The major dissolved componentin a weak base solution is the un-ionized base. Other examples of basesthat produce so few OH� ions that they are considered to be weak basesare Al(OH)3, and Fe(OH)3.

Weak Is Not InsignificantAlthough most acids and bases are classified as weak, their behavior is

extremely significant. Most of the acid-base chemistry in living systemsoccurs through interactions between weak acids and bases. For example,amino acids, the small molecules that serve as the building blocks of pro-teins, have properties of both weak acids and weak bases. The amino portionof the molecule acts as a base when it comes into contact with a strong acid,and the acid part of the molecule acts as a weak acid when exposed to a base.The coiling of the DNA into a double helix is also due to the interactionsbetween weak acids and bases. Weak does not mean “insignificant.”

Strength Is Not ConcentrationAlthough the terms weak and strong are used to compare the strengths

of acids and bases, dilute and concentrated are terms used to describe theconcentration of solutions. The combination of strength and concentra-tion ultimately determines the behavior of the solution. For example, it ispossible to have a concentrated solution of a weak acid or weak base or adilute solution of a weak acid or weak base. Similarly, you can have a concentrated solution of a strong acid or strong base, as well as a dilutesolution of a strong acid or strong base.

The pH ScaleBecause of the range of solution concentration,

the range of possible concentrations of hydroniumions and hydroxide ions in solutions of acids orbases is huge. For example, a 6M solution of HCl hasan H3O

� molarity of 6M, but a 6M solution ofHC2H3O2 has an H3O

� molarity of 0.01M.In most applications, the observed range of pos-

sible hydronium or hydroxide ion concentrationsspans 10�14M to 1M. This huge range of concentra-tions presents a problem when comparing differentacids and bases. To make this range of possible con-centrations easier to work with, the pH scale wasdeveloped by S.P.L. Sørenson, Figure 14.16.

Figure 14.16Developing the pH ScaleThe Danish biochemist S.P.L.Sørenson developed the pHscale in 1909 while workingon brewing beer. pH is anabbreviation in French for“pouvier d’hydrogene” or, in English, the “power ofhydrogen.”


Balancing pH in CosmeticsWith so many shampoos available, you may find

it hard to know which type is best for your hair.Advertisements for each type tell you that theirshampoo has more to offer than any other sham-poo. How can you know which one to choose?

Cosmetic chemists have many tools for deter-mining the effect of their products on differenthair types. Using one technique, developed byNASA, they place a hair under a microscope con-nected to a TV screen that is hooked up to a com-puter. The computer evaluates the hair before andafter treatment with the shampoo. Working withdifferent types of hair allows these chemists todetermine the best treatment for each type of hair.

Shampoos and pH balance The clear, outer layerof a strand of hair is the cuticle, which consists ofthe protein keratin. The cells of the cuticle arearranged like overlapping shingles. Shampoos thathave a high pH make the entire hair shaft swelland push the cells of the cuticle away from the restof the shaft. Harsh basic substances in solutionsfor permanents and hair coloring dissolve some ofthe cuticle, damaging the hair. Hair can also bedamaged by the sun and excessive blow drying.Damaged hair is dull and dry.

In contrast, acidic substances in shampoos oflow pH make the hair shaft tight and smooth byshrinking it and causing the cells of the cuticle tolie flat. Low-pH shampoos help restore damagedhair to its original condition and make it shineagain. They also strengthen the keratin andincrease the flexibility and elasticity of the hair.People with coarse, curly hair can benefit fromusing alkaline or high-pH shampoos. These prod-ucts soften and relax the hair, making it softer andless curly.

Why balance pH in skin products? The outerlayer of skin has a keratin structure just as hair does.Products aimed at making the skin look brighterand clearer have a higher pH. Their purpose is to

remove the top layer of keratin, which may consistof dead cells. The new cells underneath look freshand vibrant. Occasional use of these products maybe helpful, but regular use damages healthy skin byremoving too many layers of cells.

Another problem with basic skin products isrelated to an acid mantle that bathes the top layer ofthe skin, the epidermis. This fluid—composed ofoil, sweat, and other cell secretions—is a naturaldefense against bacterial infections. Strongly basicsoaps can neutralize the protective acid mantle.People with acne or oily skin must be careful not toremove the acid mantle.

Exploring Further

1. Inferring If you live in an area where the wateris hard, your hair may look dull. Why wouldrinsing with water to which lemon juice hasbeen added help?

2. Thinking Critically Why would a person withacne use skin products that are pH-neutral ormildly acidic?

Chemistry

To learn more about the chemical reasoningbehind commercial beauty tips, visit the ChemistryWeb site at chemistryca.com

http://chemistryca.com


What is pH?pH is a mathematical scale in which the concentration of hydronium

ions in a solution is expressed as a number from 0 to 14. A scale of 0 to 14is much easier to work with than a range from 1 to 10�14 (100 to 10�14).The pH scale is a convenient way to describe the concentration of hydroni-um ions in acidic solutions, as well as the hydroxide ions in basic solutions.

Think about the pH numbers 0 to 14 and the hydronium ion concen-tration range. Notice that the pH value is the negative of the exponent ofthe hydronium ion concentration. For example, a solution with a hydro-nium ion concentration of 10�11M has a pH of 11. A solution with a pHof 4 has a hydronium ion concentration of 10�4M.

How do these numbers relate to hydroxide ion concentrations? Experi-mental evidence shows that when the hydronium ion concentration andthe hydroxide ion concentration in aqueous solution are multipliedtogether, the product is 10�14. So, if the pH of a solution is 3, the hydro-nium ion concentration is 10�3M , and the hydroxide ion concentration is 10�14/10�3M , which is 10�14�(�3)M , or 10�11M.

Find the pH of each of the following solutions.1. The hydronium ion concentration equals:

a) 10�5M b) 10�12M c) 10�2M

2. The hydroxide ion concentration equals:

a) 10�4M b) 10�11M c) 10�8M

PRACTICE PROBLEMS

Figure 14.17Measuring pHpH is convenient becausethere are simple methods formeasuring it in the lab or inthe field.

� pH meters are instruments thatmeasure the exact pH of a solution.

Indicators register differentcolors at different pHs. Aconvenient way to store indicators is by soaking stripsof paper in them and thendrying the paper. Indicatorpaper is frequently soldbecause it is easy to use. �

There are several easy ways to measure pH. Two common methods areshown in Figure 14.17.

For more practice with solvingproblems, see SupplementalPractice Problems,Appendix B.

Interpreting the pH ScaleThe pH scale is shown in Figure 14.18. The scale is divided into three

areas. If a solution has a pH of exactly 7, the solution is said to be neutral.It is neither acidic nor basic.

AntacidsMany people experience a burning sensation known as heartburn

after eating certain foods. Heartburn is caused by excess acid in thestomach and esophagus. Use your knowledge of acid chemistry to eval-uate the effects of antacids that are commonly used to treat heartburn.

Procedure1. Obtain four snack-size zipper-

closure bags, and mark eachwith the name of an antacid tobe tested.

2. To each of the four bags, add 5 mL of white vinegar, 10 mLof water, and enough cabbagejuice indicator (probably 30 to40 drops) to impart a distinctcolor.

3. Add the appropriate antacidtablet to each bag, squeeze outthe excess air, and zip the bagclosed. Be sure that the antacidtablet is immersed in the vine-gar solution.

4. Squeeze the antacid tablets tobreak them into small pieces.Record your observations.

2


When the reactions have ceasedor slowed markedly, note andrecord the colors and approxi-mate pH values of thesolutions. Consult thepH-color chart fromthe ChemLab on thenext page.

Analysis1. Describe the different ways

in which the antacids react-ed with the vinegar. Inferwhich of the antacids con-tain carbonates. Explain youranswer.

2. Which of the antacids createdthe most basic final solution?Explain this answer in terms ofhow well the antacid works.

Figure 14.18The pH ScaleA pH of 7 is neutral. A pH lessthan 7 is acidic, and a pHgreater than 7 is basic. As thepH drops from 7, the solutionbecomes more acidic. As pHincreases from 7, the solutionbecomes more basic. Theflowers shown arehydrangeas. Their blooms areblue when the plants are inacidic soil and pink when thesoil is basic.

More acidic More basic

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

Neutralˇ

ˇ ˇ


Household Acids and BasesIndicators often are used to determine the

approximate pH of solutions. In this ChemLab,you will make an indicator from red cabbage anduse the indicator to determine the approximatepH values of various household liquids. The cab-bage juice indicator contains a molecule, antho-cyanin, that accounts for the color changes.

ProblemWhat are the approximate pH values of vari-

ous household liquids?

Objectives

•Measure and compare the pH values for vari-ous household liquids.

•Compare the functions of the liquids to theirchemical makeup.

Materialsred cabbage toothpickshot plate solutions of:beaker tongs eyewash100-mL beakers (2) lemon juicedistilled water white vinegarmicrotip pipets (9) table salt96-well microplate soappiece of white paper baking soda100-mL graduated borax

cylinder drain cleaner

Safety Precautions

Use beaker tongs to handle hot beakers. Wearan apron and goggles. Some of the solutions tobe tested are caustic, especially the drain cleaner.Avoid all contact with skin and eyes. If contactoccurs, immediately wash with large amounts ofwater and notify the teacher.

1. Tear a red cabbage leaf into small pieces, andlayer the pieces in a 100-mL beaker to a depth ofabout 2 cm. Add about 30 mL of distilled water.

2. Set the beaker on a hot plate, and heat untilthe water has boiled and become a deep pur-ple color. Remove the beaker from the hotplate using beaker tongs, and allow it to cool.Pour off the cabbage juice indicator liquid intoa clean beaker.

3. Set a clean microplate on a piece of white paper.Use the pipets to add 5 drops of eyewash to wellH1, lemon juice to H2, white vinegar to H3, andsolutions of table salt to H4, soap to H5, baking

Indicator color Relative pHbright redredreddish purplepurpleblue greengreenyellow

strong acidmedium acidweak acidneutralweak basemedium basestrong base

SMALLSCALESMALLSCALE


soda to H6, borax to H7, and drain cleaner toH8. Use a clean pipet for each solution.

4. Draw the cabbage juice indicator solution intoa clean pipet, and add 5 drops to each of thesolutions in wells H1-H8. Stir the solution ineach well with a clean toothpick.

5. Looking down through the wells, note andrecord the color of each solution in a datatable such as the one shown. Using the colorchart, record in the data table the approximatepH of each of the solutions.

1. Interpreting Data Are food items such aslemon juice or vinegar acidic or basic? Thesesolutions are either tart or sour, so what ionprobably accounts for this characteristic?

2. Interpreting Data Were the cleaning solu-tions acidic or basic? What ion is probablyinvolved in the cleaning process?

3. Observing and Inferring How can youaccount for the great pH difference betweenlemon juice (citric acid solution) and eyewash(boric acid solution)?

4. Using Variables, Constants, and ControlsSuppose that, in addition to the solutions, youtested a well containing pure distilled water.What purpose would this test serve?

1. Would your indicator work well to determinethe pH of ketchup? Explain.

2. You may have noted that some shampoos aredescribed as pH-balanced. What do the manu-facturers mean by this phrase? Why wouldthey do this to a soap or detergent?

3. Hypothesize about how other solutions athome would react with the cabbage juice indi-cator. Explain your predictions.

Solution Color Approximate pH

Eyewash

Lemon juice

White vinegar

Table salt

Soap

Baking soda

Borax

Drain cleaner


As the pH decreases, the concentration of hydronium ions increases, andthe concentration of hydroxide ions decreases. Every one unit decrease in thepH means a factor of 10 increase in the hydronium ion concentration. Forexample, a solution with a pH of 4 and a solution with a pH of 3 are bothacidic because their pHs are less than 7. The solution with a pH of 3 has tentimes the concentration of H3O

� of the solution with a pH of 4. Smallchanges in pH can mean big changes in hydronium ion concentration.

Similarly, as the pH increases above 7, the concentration of hydroxideions increases, and the concentration of hydronium ions decreases. Forexample, suppose you have a solution with a pH of 10 and another solu-tion with a pH of 11. The solution with a pH of 11 has ten times morehydroxide ions than the solution with a pH of 10. The solution with a pHof 11 has one-tenth the concentration of hydronium ions of the solutionthat has a pH of 10.

In a neutral solution, the concentration of hydroxide ions and the con-centration of hydronium ions are equal. Figure 14.19 compares hydroxideand hydronium ion concentrations for several solutions with different pHs.

Figure 14.19Comparison of ConcentrationsLook at the hydronium ionand hydroxide ion concentra-tions for three common solu-tions. For each solution, whatis the product of the two con-centrations?

Figure 14.20pH of Common MaterialsThe pH of an item may varydepending upon the solutionconcentration, the brand tested, and other variables.

Con

cent

ratio

n (M

)

Carbonatedwater

Stomachacid

Householdammonia

101010101010101010101010101010

0

–1

–2

–3

–4

–5

–6

–7

–8

–9

–10

–11

–12

–13

–14

Hydronium ionHydroxide ion

H3O+

concentrationin M

100

pH

10–1 10–2 10–3 10–4 10–5 10–6 10–7

NeutralAcidic Basic

10–8 10–9 10–10 10–11 10–12 10–13 10–14

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

Lemon juice(pH 2.2-2.4)

Milk(pH 6.4)

Baking soda(pH 8.4)

Drain cleaner(pH 14.0)

11

Householdammonia(pH 11.9)

Vinegar(pH 2.4-3.4)


pH of Common SubstancesFigure 14.20 gives the pHs of some common materials. Notice the

range of pHs from the low pH of lemon juice to the high pH of draincleaner.

Compare the pHs of vinegar and milk. Depending upon the brand andtype of vinegar, the pH ranges from 2.4 to 3.4. If you have a bottle ofvinegar with a pH of 3.4, the vinegar is definitely acidic. Milk, with a pHof 6.4, is also acidic, but much less so. The difference between 3.4 and 6.4(3 pH units) may not seem like much, but remember that each unit of pHrepresents a power of 10. The hydronium ion concentration of the vine-gar is 103, or 1000, times the hydronium concentration in the milk.

Using Indicators to Measure pHPerhaps you’ve been to a swimming pool and have seen someone test-

ing the water as in Figure 14.21. Among the tests done on swimming poolwater is a test for pH by using indicators. The pH tells the condition ofthe water and its suitability for swimming.

The colored solutions that are used in this test are indicators that havedifferent colors at different pHs. These dyes are not as precise as a pHmeter, but they allow you to find approximate pH by comparing the colorto a standard chart. Figure 14.22 on the next page shows the colors ofseveral indicators at different pHs. By choosing the right combination ofthese indicators, you can estimate pH across the entire pH range.

Figure 14.21Checking Pool WaterA check of the pH of thewater in a swimming pool isquick, easy, and inexpensive.Water that is not within a cer-tain range of pH can harmskin or encourage the growthof bacteria.

See page 869 inAppendix F for

Testing for Acid Rain

Lab


Connecting IdeasYou may have noticed that this chapter, which introduces the properties

of acids and bases, follows a chapter that focuses on the properties ofwater. Although acids and bases have different properties, the commonlink between the two is the role that water plays in making the chemistryof acids and bases happen.

Except for those cases where ionic hydroxides dissolve in water to formfree hydroxide ions, the behavior and strength of acids and bases are dueto their ability to cause hydrogen ions to move to water molecules froman acid or from water molecules to a base. This movement of hydrogenions between particles in solution can be used to demonstrate differenttypes of acid-base reactions.

Understanding Concepts1. Classify the following acids and bases as strong

or weak: NH3, KOH, HBr, HCHO2, HNO2,Ca(OH)2.

2. What distinguishes a strong acid or base from aweak acid or base? Are there more strong acidsand bases or weak acids and bases?

3. Other than water molecules, what particle hasthe highest concentration in an aqueous solu-tion of ammonia? What has the lowest concen-tration? Why?

Thinking Critically4. Interpreting Data The pH of normal rain is

about 5.5 due to dissolved CO2. Consider asample of rainfall with a pH of 3.5. How doesthe hydronium ion concentration in these tworain samples compare?

Applying Chemistry5. Finding pH A solution of unknown pH gives a

pink color with phenolphthalein indicator anda blue-gray color with universal indicator. UseFigure 14.22 to estimate the pH of theunknown solution.

SECTION REVIEW

Figure 14.22IndicatorsNotice the colors of these dif-ferent acid-base indicatorsover the pH scale. Some arebetter indicators at low pH,others at moderate pH, andyet others at high pH.

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

Cresol red

Thymol blue

Bromphenol blue

Methyl orange

Bromcresol green

Methyl red

Bromcresol purple

Alizarin

Bromothymol blue

Universal indicator

Phenol red

Phenolphthalein

Thymolphthalein

Alizarin yellow GG

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Chapter 14 Assessment 509

14.1 Acids and Bases■ Acids have a sour taste, turn litmus red, and

react with active metals, carbonates, andbases.

■ Bases have a bitter taste, a slippery feel, turnlitmus blue, and react with acids.

■ Acids ionize by losing hydrogen ions to watermolecules to form hydronium ions, H3O

�.

■ Bases form hydroxide ions, OH�, when dis-solved in water. Ionic hydroxides are basesbecause their ions dissociate. Covalent basesionize by hydrogen ion transfer from watermolecules to the base.

■ Acidic anhydrides are nonmetallic oxides thatreact with water to form acids. Basic anhy-drides are metallic oxides that react withwater to form bases.

■ Water plays a central role in the chemistry ofacids and bases.

14.2 Strengths of Acids and Bases■ Strong acids and bases completely dissociate

or ionize.

■ Most acids and bases are weak. Weak acidsand bases form few ions.

■ The structure of acids and covalent basesdetermines their strength.

■ The pH scale is a convenient way to comparethe acidity and basicity of solutions.

VocabularyFor each of the following terms, write a sentence that showsyour understanding of its meaning.

acid ionizationacidic anhydride pHacidic hydrogen strong acidbase strong basebasic anhydride weak acidhydronium ion weak base

UNDERSTANDING CONCEPTS1. Predict if the following substances will cause

an increase, decrease, or no change in pHwhen added to water.

a) NaOH d) CO2

b) H2C2O4 e) CH4

c) NH3 f) Fe2O3

2. For each of the acid reactive metals in the lastquestion, write a balanced equation that showsthe reaction of each metal with aqueoushydrochloric acid, HCl(aq).

3. Calcium carbonate is the major component oflimestone and marble. Sulfuric acid is one ofthe major components of acid rain. Write abalanced chemical reaction that shows howsulfuric acid reacts with calcium carbonate.

4. Write the chemical equation that shows theionization of the acid HBr in water.

5. Write balanced equations that show what hap-pens when NH3 and KOH are placed separatelyin water. How do these reactions differ?

6. Explain the role of water in the ionization ofan acid. Use the general equation to illustrateyour explanation.

7. Explain the role of water in the ionization of acovalent base. Use the general equation for thereaction to illustrate your explanation.

8. Citric acid, H3C6H5O7, and vitamin C (ascor-bic acid), H2C6H6O6, are polyprotic acidsfound in citrus fruits. Why are these acidsclassified as polyprotic acids? Write balancedequations that show the stepwise ionization ofthese acids in water.

9. You want to prepare magnesium acetate by anacid-base reaction. Write a reaction that willdo this.

REVIEWING MAIN IDEAS

CHAPTER 14 ASSESSMENT

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10. Give the formula of the product formed whenpotassium oxide reacts with water. Is the prod-uct an acid or a base?

11. What product forms when sulfur trioxidereacts with water? Is the product an acid or isit a base?

12. Write the formula of each of the followingacids and identify each as a diprotic, a triprot-ic, or a monoprotic acid.

a) sulfuric acidb) perchloric acidc) phosphoric acidd) hydrofluoric acide) acetic acid

13. Dimethylamine is the strongest base of thethree methyl derivatives of ammonia whiletrimethylamine is the weakest. How would thepH values of equal concentration solutions ofthese bases compare?

14. Why are soluble ionic hydroxides always strongbases?

15. What is the distinguishing factor that differen-tiates strong acids from weak acids?

16. What are the hydronium ion concentrations ofeach of the solutions in the previous question?

17. If the pH of a solution increases from 5.0 to6.0, what has happened to the hydronium ionconcentration?

APPLYING CONCEPTS18. Natural rainfall has a pH of approximately 5.5.

Write the balanced equation that shows whynatural rainfall is acidic.

19. How many times greater is the hydronium ionconcentration in natural rainfall (pH = 5.5)compared to pure water (pH = 7.0)?

20. A 0.10M solution of dihydrogen sulfide, H2S,forms a solution with a pH of 4.0. What per-cent of the original H2S molecules react withwater to form hydronium ions?

21. Each of the following solutions was preparedby dissolving enough of the compound to

make a solution that is 0.10M weak acid. ThepH of each solution is measured. Rank theacids from weakest to strongest. Suppose astrong acid had been prepared like the others.What pH would you predict for a 0.10M solu-tion of a monoprotic strong acid?a) Acetic acid b) Formic acid c) Benzoic acid

22. Blood has a pH of 7.4. Milk of magnesia, acommon antacid for upset stomachs, has a pHof 10.4. What is the difference in pH betweenthe two bases? Compare the hydroxide ionconcentrations of the two solutions.

23. Lemon juice has a pH of about 2. Should youcut a lemon on a marble surface? Explain.

24. A substance that can act as an acid or a base iscalled amphoteric. Use the chemical equationsto show how nitric acid and ammonia reactwith water to show that water is amphoteric.

25. An aqueous ammonia solution is sometimescalled ammonium hydroxide. Why?

26. Why does acid rain dissolve marble statues?Write the reaction that occurs when rain con-taining sulfuric acid reacts with a statue madeof marble, CaCO3. Calcium sulfate is one ofthe products formed.

27. Finland, a country that has been hit hard byacid rain, has used lime, CaO, to try to returnlife to acidified lakes. Why was lime used?

28. A sour taste is related to acids. A bitter taste isrelated to bases. How is a salty taste related toacids and bases?

Everyday Chemistry 29. Some people rinse their freshly shampooed

hair in diluted lemon juice or vinegar. Whymight doing this be beneficial to your hair?

Biology Connection30. After exercise, muscles sometimes become sore

because of a buildup of lactic acid. How mightthis buildup temporarily affect the acid-basebalance in the blood?


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Chapter 14 Assessment 511

Chemistry and Society31. Why might city dwellers with respiratory dis-

eases such as asthma or emphysema be advisedto stay inside on hot days?

Chemistry and Technology 32. From what you know about reactions that

acids will undergo, infer how sulfuric acidmight be used to remove unwanted materialsfrom ores.

THINKING CRITICALLYApplying Concepts33. What is the molarity of HCl, H3O

�, and Cl� ina 0.50M solution of HCl?

Relating Cause and Effect34. Estimate the molarity of HC2H3O2, H3O

�, andC2H3O2

� in 0.50M HC2H3O2.

Observing and Inferring35. Examine the formulas of several polyprotic

acids and compare them to the formulas ofseveral monoprotic acids. What element isalways present in monoprotic acids? What twoelements are usually present in polyproticacids?

Relating Cause and Effect36. Baking powder, when mixed with water, pro-

duces bubbles that make a cake rise. Fromwhat you know about the properties of acids,infer what types of compounds are containedin baking powder and what gas is contained inthe bubbles released by the reaction.

Applying Concepts37. Hard water deposits around sinks may be com-

posed of calcium carbonate and magnesiumcarbonate. You can buy commercial cleaners toremove these insoluble compounds, or youcould use something from your kitchen. Whatmight you try?

Interpreting Data38. Identify the first compound in the following

reactions as an acid or a base.

a) C5H5N � H2O ˇ C5H5NH� � OH�

b) HClO3 � H2O ˇ H3O� � ClO3

�

c) HCHO2 � H2Oˇ H3O� � CHO2

�

d) C6H5SH � H2O ˇ H3O� � C6H5S

�

39. One model of acid/base interactions focuseson the transfer of hydrogen ions in chemicalreactions. In this model, acids are the H+

donors and bases are the H+ acceptors. Use thereactions in the previous question to classifythe reactants as acids or bases.

Interpreting Chemical Structures40. What is an acidic hydrogen? Draw the dot

structure for acetic acid, and use it to explainwhy only one of the four hydrogens is acidic.

Observing and Inferring41. ChemLab What would you expect the pH of

an aqueous solution of the salt calcium chlorideto be?

Forming a Hypothesis42. MiniLab 1 Small pieces of zinc must be added

to the acids instead of powdered zinc. Hypoth-esize why powdered zinc can’t be used safely.

Observing and Inferring43. MiniLab 2 Examine antacid ingredient lists.

Some antacid tablets contain ingredients otherthan the antacid itself. What are some of theseingredients? Infer why the presence of theseingredients might affect the amount of antacidcontained in an antacid tablet.

CUMULATIVE REVIEW44. Write a balanced equation for each of the fol-

lowing reactions involving acids and bases, andclassify each reaction as one of the five generalreaction types. (Chapter 6)

a) the reaction of water and lime to form cal-cium hydroxide

b) the reaction of sulfuric acid with zincc) the reaction of nitric acid with aqueous

potassium hydroxide



45. What is the molar mass of each of the follow-ing substances? (Chapter 12)

a) calcium carbonateb) chlorine gasc) ammonium sulfate

46. How many grams of sodium hydroxide areneeded to prepare 2.50 L of 2.00M NaOH?(Chapter 13)

SKILL REVIEW47. Making and Using Tables Complete each row

of the table below using the information pro-vided. For some cells, there is more than onepossible correct answer. Assume that all sub-stances are dissolved in pure water, and thesolutions all have a molarity of 0.10M.

48. Designing an Experiment Design an experi-ment to determine the best material to use tostore lemon slices. Explain your conclusions.

49. Sequencing Create a bar graph that showssolutions with the following pHs in order fromthe most acidic to the most basic: 7.6, 9.8, 4.5,2.3, 4.0, 11.6.

WRITING IN CHEMISTRY50. Find out about how sulfuric acid is made and

its many commercial uses. Write an advertise-ment for sulfuric acid, including any researchinformation you found out. Include graphicsthat illustrate things such as uses of the acid ora graph that indicates the amount of produc-tion by different countries.

PROBLEM SOLVING51. A student buys some distilled water. She mea-

sures the pH of the water and finds it to be 6.0.She then boils the water, fills a container to thetop with the hot water, and puts a lid on the con-tainer. When the water is at room temperature,the pH is 7.0. The student pours half the waterinto one container and stirs it for five minutes.She blows air through a straw into the other sam-ple of water. She measures the pH of the samplesof water and finds it to be 6.0 in both samples.Write an entry in your Science Journal thatexplains this series of pH measurements.

Acetic acid

HCl

Acid Strong

Ammonia

LiOH

Base Strong

Weak �7

Neutral Na�, Cl�

H�, NO3�

Phosphoric acid

Name of Formula of Acid, Base, Strong or Weak pH: �7, �7, Major Particle(s)Substance Substance or Neutral Electrolyte or 7 Litmus Color in Solution


Standardized Test Practice 513

1. Acids are defined as substances that

a) produce hydronium ions in water.b) have hydrogen in their compounds.c) produce hydroxide ions in water.d) neutralize bases.

2. A triprotic acid is

a) an acid with three hydrogen atoms.b) an acid with three acidic hydrogen atoms.c) an acid with three hydronium ions.d) an acid with three extra protons.

3. Which of the following is the best descriptionof the total conversion of the diprotic succinicacid (H2C4H4O4) into hydronium ions?

a) H2C4H4O4(aq) → HC4H4O4�(aq) �

H3O(aq)b) H2C4H4O4(aq) → H2C4O4

2�(aq) �H3O

�(aq)c) H2C4H4O4(aq) → HC4H4O4

�(aq) �H3O(aq) → C4H4O4

2�(aq) � H3O�(aq)

d) H2C4H4O4(aq) → H2C4H3O4�(aq) �

H3O�(aq) → H2C4H2O4

2�(aq) �H3O

�(aq)

4. Bases are defined as substances that

a) produce hydronium ions in water.b) have hydrogen in their compounds.c) produce hydroxide ions in water.d) neutralize acids.

5. Which of the following is a strong acid?

a) NaOH c) H3O+

b) HC2H3O2 d) HCl

6. Which of the following compounds is a basicanhydride?

a) CO2 c) CaOb) SO2 d) NO2

Use the table in the next column to answer questions 7–9.

7. What is the pH of apples?

a) �3 c) �10b) 3 d) 10

8. The concentration of hydronium ions in eyewash is

a) 3 times greater than the concentration ofhydronium ions in lemons.

b) 3 times less than the concentration ofhydronium ions in lemons.

c) 1,000 times greater than the concentrationof hydronium ions in lemons.

d) 1,000 times less than the concentration ofhydronium ions in lemons.

9. The concentration of hydroxide ions in apples is

a) 10�11M.b) 1011M.c) 10�3M.d) 103M.

10. What is the H3O+ ion concentration of house-

hold ammonia?

a) 10�2M.b) 102M.c) 10�12M.d) 1012M.

Standardized Test Practice

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Substances H3O� concentration in M pH

Eyewash ? 5

Apples 10�3 ?

Lemons 10�2 ?

Lye 10�14 ?

Householdammonia ? 12

Don’t Be Afraid To Ask For Help If you’repracticing for a test and you find yourself stuck,unable to understand why you got a questionwrong, or unable to answer it in the first place, asksomeone for help. As long as you ask for helpbefore the test, you’ll do fine!

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