8.4 Strength of Acids and Bases

Reading StrategyComparing and Contrasting Copy theVenn diagram below. As you read, completethe diagram by comparing and contrastingacids and bases.

Key ConceptsHow is pH used to describe theconcentration of acids and bases?

How do strong acids and bases differ fromweak acids and bases?

Why are strong acids andbases good electrolytes?

Vocabulary◆ pH◆ buffer◆ electrolyte

On a hot summer day, you might go swimming in a pool with someof your friends. As the water evaporates from your skin, you feel coolerand refreshed.

Have you ever thought about how the water in a swimming poolis made safe for swimming? You may have noticed the odor of chlorineat a backyard swimming pool or at larger municipal pools. Certaincompounds of chlorine are dissolved in the water. These compoundsprevent the growth of bacteria that could make you sick.

The concentration of hydronium ions insolution must be carefully controlled in aswimming pool. If there are too many or toofew hydronium ions, then the right com-pounds of chlorine will not be present.Figure 21 shows a pool maintenance workeradding sodium bicarbonate, NaHCO3, to thewater. Sodium bicarbonate can be used tolower the concentration of hydronium ionsin solution.

How can you describe the acidity orbasicity of a solution? One way is to deter-mine the concentration of hydronium orhydroxide ions present in solution. Anotherway is to describe how readily those hydro-nium ions or hydroxide ions formed.

Strongacid

Strongbase

b. ? a. ? c. ?

246 Chapter 8

Figure 21 Sodium bicarbonate, orbaking soda, is often added toswimming pools to regulate theacidity of the water.

246 Chapter 8

FOCUS

Objectives8.4.1 Define pH, and relate pH to

hydronium ion concentrationin a solution.

8.4.2 Distinguish between strongacids and weak acids, andbetween strong bases andweak bases.

8.4.3 Define buffer, and describehow a buffer can be prepared.

8.4.4 Explain how electrolytes canbe classified.

Build VocabularyWord Meanings Ask students tobrainstorm examples of productadvertising that contain the terms pH,electrolyte, or buffer. (Students may haveheard of beauty products described as“pH-balanced,” some sports beveragescontain electrolytes, and many antacidscontain buffers.) Have students look upthe definition of each term and specu-late what is meant by the advertisers’claims. (Answers may include that somedeodorants differ in acidity, sports drinkscontain ions in solution, and someantacids can be used to resist largechanges in pH.)

Reading Strategya. Ionizes almost completely whendissolved in waterb. Is a strong electrolyte c. Dissociates almost completely whendissolved in water

INSTRUCTBuild Reading LiteracyIdentify Main Idea/Details Refer topage 98D in Chapter 4, which providesthe guidelines for identifying main ideaand details.

Have students read the section andmake a list of the main headings oneach page. Under each heading, havethem identify the main idea of thepassage. Have students refer to their listswhen answering the questions in theSection 8.4 Assessment.Verbal

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Reading Focus

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Section 8.4

Print• Guided Reading and Study Workbook

With Math Support, Section 8.4• Transparencies, Section 8.4

Technology• iText, Section 8.4• Presentation Pro CD-ROM, Section 8.4• Go Online, NSTA SciLinks, pH

Section Resources

Solutions, Acids, and Bases 247

0

Car battery acid Lemons Oranges

Vinegar Tomato

White bread Distilled water

Milk

Soap

Baking soda

Most acidic Most basic

Ammonia

Drain cleaner

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

Neutral

The pH ScaleChemists use a number scale from 0 to 14 to describe the concentra-tion of hydronium ions in a solution. It is known as the pH scale. ThepH of a solution is a measure of its hydronium ion concentration. ApH of 7 indicates a neutral solution. Acids have a pH less than 7. Baseshave a pH greater than 7.

Notice in Figure 22 that water falls in the middle of the pH scale.Water ionizes slightly according to the following reaction.

2H2O H3O� � OH�

The arrow pointing to the left is longer than the arrow pointing to theright to show that water contains more molecules than ions. Water isneutral because it contains small but equal concentrations of hydro-nium ions and hydroxide ions. At 25°C, the concentration of bothH3O� and OH� in water is 1.0 � 10�7 M. Pure water has a pH of 7.

If you add an acid to water, the concentration of H3O� increasesand the concentration of OH� decreases. Suppose you have a hydro-chloric acid solution in which the concentration of H3O� is 0.10 M (or1.0 � 10�1 M). The solution has a pH of 1. The lower the pHvalue, the greater the H3O� ion concentration in solution is.

If you add a base to water, the concentration of OH� increasesand the concentration of H3O� decreases. Consider a sodiumhydroxide solution in which the concentration of OH� is 0.10 M. Theconcentration of H3O� in this solution is 1.0 � 10�13 M, which cor-responds to a pH of 13. The higher the pH value, the lower theH3O� ion concentration is.

Strong Acids and BasesRecall that some reactions go to completion while others reach equi-librium. When certain acids and bases dissolve in water, the formationof ions from the solute almost goes to completion. Such acids and basesare classified as strong.

What is the pH of pure water?

Figure 22 The pH scale canhelp you classify solutions asacids or bases. Comparing and ContrastingThe desired pH range ofchlorinated water in swimmingpools is 7.2 to 7.8. How does theconcentration of hydronium ionsin this solution compare to thatof lemon juice?

For: Links on pH

Visit: www.SciLinks.org

Web Code: ccn-1084

The pH Scale Use VisualsFigure 22 Have students examineFigure 22 of the pH scale. Ask, In whichdirection would you find substancesthat are more acidic? (To the left)Would a solution with a pH of 11 be anacid or a base? (A base) What is the pHof ammonia? (11.5) Compare the pHand acidity of oranges and tomatoes.(Oranges have a lower pH than tomatoesand are therefore more acidic.) Visual

Build Math SkillsExponents Many students have a hardtime interpreting positive and negativeexponents. Be sure that they understandthat a value with a large negative expo-nent is significantly smaller than a valuewith a small negative exponent. Logical

Direct students to the Math Skills inthe Skills and Reference Handbookat the end of the student text foradditional help.

Strong Acids and BasesIntegrate BiologyExplain that the stomach contains adilute solution of hydrochloric acid, HCl.Even though the solution is dilute, HCl isa strong acid, which means it ionizescompletely in solution. Have studentsfind out how this strong acid aids indigestion. Have them make a posterillustrating the stomach’s role indigestion and explain how food isdigested by stomach acid. (Stomachacid works with enzymes to help breakdown proteins. Contraction of stomachmuscles helps to mix the food, acid, andenzymes, turning food into a semiliquid.)Visual, Verbal

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Solutions, Acids, and Bases 247

Customize for English Language Learners

Think-Pair-ShareHave students work in pairs to think of otherscales besides pH, and the quantities that theymeasure. Examples include temperature scales,hardness scales, and the Richter scale.

Strengthen discussion skills by having studentsshare their examples with the class. Encouragestudents to refer to Figure 22 and makecomparisons between pH and other scales.

Answer to . . .

Figure 22 Concentration of hydro-nium ions in lemon juice is greater.

7

Download a worksheet on pH forstudents to complete, and findadditional teacher support fromNSTA SciLinks.

Making a Battery

Materials1 large fresh lemon, plasticknife, zinc strip, 2 copper strips,multimeter

Procedure1. Roll the lemon between

your hands until it softens.

2. Use the knife to carefullycut two parallel slits in thelemon about 1 cm apart.Push the copper strips intothe slits to a depth of 2 to 3 cm. Don’t allow the strips to touch.

3. Attach the copper strips tothe terminals of themultimeter. Observe thereading and record it.

4. Replace one of the copperstrips with the zinc stripand repeat step 3.

Analyze and Conclude1. Observing What was

the reading on themultimeter when you used two copper strips? A copper and a zinc strip?

2. Predicting Lemon juice is acidic. Would a basicsolution provide a similar result?

248 Chapter 8

Strong Acids When hydrogen chloride dissolves in water, almost allof its molecules ionize. After the reaction, there are about the samenumber of hydronium ions in solution as there were molecules of HCl tobegin with. The products do not reform reactant molecules. HCl is anexample of a strong acid. When strong acids dissolve in water, theyionize almost completely. Other strong acids include sulfuric acid,H2SO4, and nitric acid, HNO3.

Strong Bases When dissolved in water, sodium hydroxide almostcompletely dissociates into sodium and hydroxide ions. Sodium hydrox-ide is an example of a strong base. Strong bases dissociate almostcompletely in water. Other strong bases include calcium hydroxide,Ca(OH)2, and potassium hydroxide, KOH.

Weak Acids and BasesThe citric acid in orange juice and the acetic acid in vinegar are weakacids. Toothpaste and shampoo contain weak bases. Weak acidsand bases ionize or dissociate only slightly in water.

Weak Acids A solution of acetic acid, CH3COOH, and water canbe described by the following equation.

CH3 COOH � H2O CH3 COO� � H3O+

The equilibrium favors the reactants over the products, so few ionsform in solution. A weak acid forms fewer hydronium ions than astrong acid of the same concentration. This also means that a weakacid has a higher pH than a strong acid of the same concentration.

It is important to understand the difference between concentra-tion and strength. Concentration is the amount of solute dissolved ina given amount of solution. Strength refers to the solute’s tendency toform ions in water. You cannot assume that a strong acid has a low pH,because its concentration also affects pH. For instance, a dilute solu-tion of HCl (a strong acid) can have a pH of 6. But a concentratedsolution of acetic acid (a weak acid) can have a pH of 3.

Weak Bases Ammonia, NH3, is a colorless gas with a distinctivesmell. When it dissolves in water, very little of it ionizes. Equilibriumfavors the reactants, so few NH4

+ and OH– ions are produced.

NH3 + H2O NH4+ + OH–

Buffers Weak acids and bases can be used to make buffers. A bufferis a solution that is resistant to large changes in pH. Buffers can be pre-pared by mixing a weak acid and its salt or a weak base and its salt.Because a buffer can react with both an acid and a base, its pH remainsrelatively constant.

Weak Acids and Bases

Making a Battery

ObjectiveAfter completing this activity, studentswill be able to • make a battery using a lemon as a

source for electrolytes.

Skills Focus Observing, Predicting

Prep Time 5 minutes

Advance Prep Use tin strips to cutcopper and zinc into 2–5 cm strips. Stripthe ends if using insulated wires. Filedown the rough edges of the metalstrips. Wear heavy leather gloves whenpreparing the strips.

Class Time 10 minutes

Safety Have students observe safetysymbols and wear lab aprons.

Teaching Tips • Have students throw used lemons away.• Clean used copper and zinc strips and

save them for reuse.• Current is the rate at which charge

flows through a wire and is expressedin amps, while voltage is expressed involts. Potential difference is a measureof the work required to carry positivecharge from one point to another andis expressed in volts.

Expected Outcome The battery willprobably produce less than 1 volt and avery small current, about 0.0001 amp.The actual voltage and current dependon how juicy the lemon is, how far apartthe electrodes are placed, and how deepthey go into the fruit.

Analyze and Conclude1. There is no voltage when using twocopper strips. Values between 0.5 V and 1 V are typical when using the copperand zinc strips. 2. A basic solution is also electrolytic and may provide a similar result. Visual, Kinesthetic

For EnrichmentHave students perform this lab withmetals to determine which pairs of metalsproduce the greatest voltages. Then, referthem to a chemistry text to read aboutelectronegativity. (Pairs of metals that are far apart in the electromotive seriesproduce the greatest voltages.)Kinesthetic

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Section 8.4 (continued)

Buffered Aspirin Many drugs containbuffers to offset the effects they might haveupon ingestion. For example, acetylsalicylicacid is the ingredient in aspirin medication

that relieves pain. Many of the kinds of aspirinavailable for consumer use are buffered tominimize the acidity of aspirin.

Facts and Figures

248 Chapter 8

Section 8.4 Assessment

Reviewing Concepts1. How is pH related to the concentration of

hydronium ions in solution?

2. What determines the degree to which an acid or base is weak or strong?

3. Are strong acids and bases goodelectrolytes? Explain why or why not.

4. Why is pure water neutral?

5. What is a buffer?

Critical Thinking6. Comparing and Contrasting Explain how

the concentration of an acid differs from thestrength of an acid.

7. Relating Cause and Effect Suppose youadd another liter of water to 1 liter of a 1-molar solution of hydrochloric acid. Whathappens to the number of hydronium ions insolution? What happens to the concentration?

Explanatory Paragraph Explain the con-cept of a pH scale, and compare the pH val-ues of acids, bases, and pure water. (Hint:Use examples from Figure 22 to help youdescribe the range of the pH scale.)

Solutions, Acids, and Bases 249

ElectrolytesSports drinks, like the one shown in Figure 23, tastesalty because they contain salts of elements such assodium, potassium, and calcium. Salts are examplesof electrolytes. An electrolyte is a substance that ion-izes or dissociates into ions when it dissolves in water.The resulting solution can conduct electric current.The electrolytes in sports drinks help restore the bal-ance of ions in your body.

Electrolytes can be classified as strong or weak.Strong acids and bases are strong electrolytes

because they dissociate or ionize almost com-pletely in water. For example, sodium hydroxide isa strong electrolyte that produces many ions inwater. Salts are also strong electrolytes. When potas-sium chloride dissolves in water, it dissociates intopotassium and chloride ions. In contrast, acetic acid is a weak elec-trolyte because it only partially ionizes.

Batteries and other portable devices that produce electricity alsocontain electrolytes. Car batteries use lead plates in combination withthe electrolyte sulfuric acid to produce electricity. Space shuttles usedevices called fuel cells that provide electricity to power all the crafts’devices. Fuel cells use the strong base potassium hydroxide as an elec-trolyte. Instead of metal electrodes, the fuel cells use oxygen andhydrogen brought from Earth. At the same time that the fuel cells provide electrical energy to power a space shuttle, they also producewater that the crew can use.

Figure 23 Drinking sports drinksafter exercising can restore thebalance of ions in your body.

Electrolytes

Many students think that pure water is agood conductor of electricity. Thoughpure water has some ions due to self-ionization, the number of ions in purewater is not great enough to carry anelectric current. Explain that practicallyall water obtained from traditionalsources contains electrolytes. Thus, it isvery difficult to find water that will notconduct electricity. Even deionizedwater samples may have some dissolvedions depending on the effectiveness ofthe deionizer or the method of storage.Verbal

ASSESSEvaluateUnderstandingEncourage students to make a note cardfor each of the Key Concepts questionslisted on p. 246. Then, ask them tomake a note card that answers eachquestion using one of the boldfaced keypoints in this section. Have them makethree more sets of note cards using thevocabulary terms and their definitions.Encourage students to review theinformation on their cards.

ReteachAs a class, make a chart that lists whatstrong acids, strong bases, and strongelectrolytes have in common. Do thesame for weak acids, weak bases, andweak electrolytes.

Acceptable answers include explainingthat a pH scale allows you to describehow acidic or basic a solution is.Solutions with a pH lower than 7, suchas vinegar, are acidic. Solutions with apH higher than 7, such as householdammonia, are basic. Solutions with a pHof 7 (the same as pure water) are neutral.

If your class subscribes toiText, use it to review key concepts inSection 8.4.

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Solutions, Acids, and Bases 249

4. Pure water is neutral because it containsequal concentrations of hydronium andhydroxide ions.5. A buffer is a solution that is resistant to largechanges in pH.6. The concentration of an acid is the amount ofsolute dissolved in a given amount of solution.The strength of an acid refers to the solute’stendency to form ions in water.7. The number of hydronium ions stays thesame. The concentration decreases becausethere are fewer ions per liter.

Section 8.4 Assessment

1. Solutions with a low pH have a high concen-tration of hydronium ions in solution and areacidic. Solutions with a high pH have a lowconcentration of hydronium ions in solution and are basic.2. The degree to which an acid or basedissociates or ionizes when dissolved in waterdetermines whether it is weak or strong.3. Strong acids and bases are strongelectrolytes because they dissociate or ionizealmost completely when dissolved in water.

River of Life

Liquid tissueBlood is a mixture of cells—red blood cells,white blood cells, and platelets—suspendedin a water-based solution called plasma.Nutrients, vitamins, and minerals also travelin blood, dissolved in the plasma. The cellsand other substances remain suspended inthe blood because the heart’s pumpingaction keeps the blood moving.

Just as rivers are used to transport products and rawmaterials, blood connects the body’s living cells, deliveringnutrients and carrying away wastes. The exact compositionof this red liquid changes continuously as it flowsthrough the body.

Whiteblood cell

Redbloodcell

White blood cells andplatelets White blood

cells help the body fightdisease. Platelets help the

blood to clot whenbleeding occurs.

Red blood cells These cellscontain the compound

hemoglobin, which carriesoxygen from the lungs to

cells throughout the body.

Plasma This liquid part of the blood is about

90 percent water. The other 10 percent

includes many dissolvedsubstances, such as

proteins and glucose.

Blood componentsWhen left to sit, bloodseparates into its parts.

About 55 percent makes up the liquid top layer

and 45 percent makes up the cellular layer below.

250 Chapter 8

250 Chapter 8

River of LifeBackgroundWhen blood pH falls outside of the nor-mal range, 7.35–7.45, a person mayexperience acidosis or alkalosis.

Acidosis occurs when blood has a pH as low as 7.2. It can arise from the bloodhaving too much carbon dioxide due topoor breathing, production of acids dueto high glucose levels in the urine (asymptom of diabetes), and loss ofbicarbonate due to severe diarrhea.Alkalosis occurs when blood has a pHabove 7.45. It can arise from the bloodhaving too little carbon dioxide due tohyperventilation, the loss of stomachacid due to vomiting, and the presenceof high levels of bicarbonate in fluidsdelivered intravenously (through an IV).

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PlateletCells Oxygen is delivered to

each cell in the body, and carbon dioxide is removed.

Maintaining blood pH levelsFor the body to function normally, blood pHmust be kept within a narrow range. Buffersystems ensure pH levels are maintained withinthat range. A buffer is a chemical or acombination of chemicals that can absorb eitherhydrogen ions (H+) or hydroxide ions (OH–).Buffers maintain a relatively constant hydrogenion concentration. Hydrogen ions produced bychemical reactions in the body are the mainthreat to your blood’s pH. A very importantblood buffer system consists of hydrogencarbonate ions (HCO3

–) and carbonic acid(H2CO3) as shown in this equation.

Carbon dioxide (CO2) dissolved in the blood actsas an acid. It forms carbonic acid when dissolvedin water, and donates hydrogen ions when theyare needed. Hydrogen carbonate, produced bythe kidneys, is a base that soaks up hydrogenions when there are too many of them, andtransports them to the lungs where the acid isexcreted as carbon dioxide.

Lungs In the lungs, carbondioxide is removed from theblood, and oxygen is taken

up by red blood cells.

Heart The heart pumps oxygenatedblood, shown in red, from the lungsaround the body. At the same time,

the heart pumps deoxygenated blood,shown in blue, back to the lungs.

HCO + H H CO3 2 3 + –

Solutions, Acids, and Bases 251

Blood flowThe body’s circulation system

contains two circuits. In the first,blood is pumped by the heart tothe lungs. As oxygenated blood

returns to the heart, it is pumpedto the remaining tissues in the

body through the second circuit.

Build Science SkillsApplying Concepts

Purpose In this activity, students test for the presence of carbon dioxide in breath and compare the carbondioxide content of breath before and after exercise.

Materials calcium hydroxide (picklinglime); 2 large, sealable jars; clear plasticcups; straws; stopwatches; jump ropes

Class Time 25 minutes

Safety Caution students to only exhalethrough the straw. Limewater is corrosive.Have students wear safety goggles,plastic gloves, and lab aprons.

Procedure Prepare the day before asolution made of 1 tablespoon of picklinglime dissolved in 1 quart of water. Seal the jar and let it sit overnight. The nextday, carefully pour off the clear liquid intoa clean jar. Avoid transferring any of thewhite solid to the new jar. Seal the jar and save the limewater for the activity.Tell students that limewater turns cloudyin the presence of carbon dioxide. Pourinto each test cup a small amount of lime-water. Have students measure how long it takes for the solution to turn cloudywhen they exhale into a straw submersedin the solution. Do not allow them to suckany of the limewater into the straw or into their mouths. Then, ask students toperform some sort of exercise. If you areable to go outside or to the gymnasium,students may jump rope for 5–10minutes. If jump ropes are not available,students could walk briskly or do calis-thenics for several minutes. Then, havestudents perform the test with a freshsolution of limewater.

Expected Outcome Limewater turnscloudy in the presence of carbon diox-ide. The solution turns cloudy morequickly after exercise due to an increasein the levels of carbon dioxide in breath.Kinesthetic

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Using BloodBecause blood is continuously replenished by the body, it canbe taken from healthy people and made available for those whoneed it—whether because of blood loss in accidents or surgery,or to treat illnesses such as anemia or cancer.

Blood banks store blood from donors, or sometimes from apatient, for use during a planned surgery. Once collected,compounds are added to prevent clotting. Most blood isseparated into components. For example, plasma can be storedat –18˚C for up to 12 months, while platelets are stored at roomtemperature and must be used within 5 days. Charles Drew

During the 1940s, physician and inventor Charles Drewdeveloped methods forseparating and storing blood ona large scale, providing the basisfor today’s Red Cross centers.

1900: Karl Landsteinerdiscovers three of the mainblood groups (A, B, and O). The fourth group, AB, is discovered in 1902.

1932: First blood bank is established in Russia,followed in 1937 by the firstUnited States hospital bloodbank in Chicago.

1940: Charles Drewpioneers large-scaleseparation and storageof blood plasma.

1948: American Red Crossestablishes a national bloodcollection and distributionprogram.

CentrifugeA centrifuge works like the spin cycle on awashing machine to separate blood quicklyinto its different components.

Tubecontainingblood spunat high speed

252 Chapter 8

252 Chapter 8

Using BloodBuild Science SkillsInferring Explain that when a recipient’sblood serum contains antibodies thatreact to the antigens on the surface of a donor’s blood cells, it will produce apotentially fatal clumping of blood cells.Each blood type has a particular combina-tion of antigens and antibodies. You canalways receive blood of your own type.However, depending on your blood type,you may or may not be able to receiveblood of another type. Give the followinginformation to students.• Type A blood has Type A antigens on

its blood cells and anti-B antibodies inits serum.

• Type B blood has Type B antigens on itscells and anti-A antibodies in its serum.

• Type AB blood has both Type A andType B antigens on its blood cells, butneither anti-A nor anti-B antibodies inits serum.

• Type O blood contains neither A nor Bantigens on its cells but has both anti-Aand anti-B antibodies in its serum. Ask,Can you deduce which type of blooda person would need to donate toanyone? (People with Type O blood areuniversal donors.) Can you deducewhich type of blood a person wouldneed to have to be able to receive allother types? (People with Type AB bloodare universal receivers.)Logical

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Blood Types Some blood types are rarer than others. The following chart lists theapproximate percentage of each blood type in the U.S. population.

Facts and FiguresBlood Type Percentage of U.S. Population

O positive 38%A positive 34%B positive 9%O negative 7%A negative 6%AB positive 3%B negative 2%AB negative 1%

� Research and write a paragraph about thework of Charles Drew. What methods did he use to prolong the storagetime for whole blood? Whydid he decide to separatewhole blood into plasma andcells for storage?

� Take a Discovery ChannelVideo Field Trip by watching“Suspended in Blood.”

Going Further

Blood TransfusionEach year, more than 4 million people inthe United States receive a blood trans-fusion, either of whole blood or of a bloodcomponent, such as plasma or platelets.Before being stored, blood from a donoris tested to make sure it is safe.

Blood bag The use of whole blood intransfusions has been reduced in recentyears but it is retained as a treatmentoption in cases of massive blood loss.

Donated blood

1950: Plasticblood bagsare introduced forblood storage,allowing blood tobe frozen at lowertemperatures andfor longer periods.

1985: First HIVtesting of donorblood is carried out,followed by othertests to protecttransfusion patientsfrom disease.

Crossmatching bloodBlood groups are used to determine which bloodcan be given to whom. Antigens, or molecularmarkers on the surface of red blood cells,determine the type of blood a person can safelyreceive in a transfusion. If blood of incompatibletypes is mixed, the red blood cells form clumpsinstead of mixing properly. These clumps canblock blood vessels and even cause death.

Solutions, Acids, and Bases 253

Video Field Trip

Going FurtherAcceptable answers include: CharlesDrew (1904–1950) was a doctor andresearcher who discovered that bloodcould be stored longer when the plasmawas separated from the rest of the bloodand then frozen. When the plasma isrecombined with red blood cells, it canbe used for blood transfusion. If blood isfrozen without separating the cells fromthe plasma, the red blood cells willbreak down after two days. Drew alsodiscovered that plasma could be safelygiven to patients regardless of theirblood type or the type of the donor.Verbal

Use Community ResourcesArrange for a phlebotomist to visit theclass. Have the phlebotomist discuss the importance of blood type in usingblood donations for transfusions. Ifpossible, and following standard safetyprocedures, have the phlebotomistperform a blood test on student volun-teers to determine their blood type.Interpersonal

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Solutions, Acids, and Bases 253

After students have viewed the Video Field Trip, askthem the following questions: What are the mostcommonly found cells in blood? (Red blood cells)What is the function of red blood cells in theblood? (They pick up oxygen in the lungs and deliverit throughout the body.) How does the body useblood to dispose of the carbon dioxide that itproduces? (Red blood cells absorb carbon dioxide

on their way back to the lungs and release it there.)When you exercise, your body needs moreoxygen. What changes occur that deliver theextra oxygen where it is needed? (You breathefaster and your heart beats faster. As a result, theblood picks up more oxygen in the lungs and movesfaster to deliver the oxygen.) What are two otherkinds of cells found in blood, and what is theirfunction? (White blood cells attack invading bacteria,or germs, to help prevent disease. The blood alsocontains platelets that collect at cuts to block the flow of blood and to form a clot.)

Video Field Trip

Suspended in Blood