TOPIC 13 How Do You Spell Relief? 1 Ahh! After a hard day mowing the lawn or raking leaves, there isn’t anything better than the clean, refreshing taste of your favourite soft drink,

T O P I C 1

Ahh! After a hard day mowing the lawn or rakingleaves, there isn’t anything better than the clean,refreshing taste of your favourite soft drink,accompanied by a big plate of sliced vegetableswith a tangy blue cheese or sour cream dip, maybeeven a peanut butter and jelly sandwich. As youraching muscles relax and you take another sip ofthat tart, cold drink, let your thoughts wander tothe importance of acids and bases in your world.

You are already familiar with acids and bases inyour environment — you experience them on adaily basis, as shown in Figure 3.7. The tart tasteof carbonated beverages, the tang of a salad dressing,even the burning sensation in your muscles duringexertion — all are due to acidic substances. Thebitter taste of celery or radishes, the soothingaction of a sunburn lotion, the slippery feel ofsoap — these are due to basic substances.

Acids and BasesAcids and bases, the chemicals that produce acidic and basic sub-stances, have many uses in our lives. For example, phosphoric acid is akey component in the manufacture of fertilizers, detergents, and manypharmaceuticals. It is a flavouring agent in carbonated beverages,cheeses, jams, jellies — virtually any food with a tangy flavour.

Another important acid, sulfuric acid, is most familiar as the ingredi-ent of the battery for your family’s vehicle. But it is also used in themanufacture of paints and dyes, the refining of oil and gas, and theproduction of synthetic textiles. In fact, it is possible to get an approxi-mate measure of any country’s industrial activity by looking at the vol-ume of sulfuric acid used by that country.

Of the basic substances, sodium hydroxide is a component of house-hold and industrial cleaners, bleaching agents for the production ofpaper, fixatives in textile dying, solvents in the making of electronic cir-cuit boards, and as a reagent in film processing. The base, aluminumhydroxide, is a key ingredient in antacid tablets. You may need this ifyou are going to mix peanut butter and jelly with blue cheese dressing!

How Do You Spell Relief? • MHR 197

T O P I C 3 How Do You Spell Relief?

Figure 3.7 Some of theobjects in this picturecontain acids, while otherscontain bases.

The Observable Properties of Acids and Bases As you can see, acids and bases are used for very different roles, so it isimportant to be able to identify acids and bases. You probably noticedthat one of the first clues to whether a substance is acidic or basic is itstaste. Acids taste sour (e.g., lemons) and bases taste bitter (e.g., horse-radish). Unfortunately, tasting is not usually an acceptable option forlaboratory work, so you can omit this method as a means of determin-ing the basic or acidic nature of an unknown substance. Fortunately,acids and bases react differently with other substances, so we can devisetests to determine the acidic or basic nature of an unknown substance.

Likely you have experienced the slippery feel of soap (a basic sub-stance). Although that property identifies basic substances, touching anunknown liquid with your bare hands is not a good idea in any lab setting.

To safely tell whether a substance is an acid or a base, look for anoticeable colour change that occurs when an acid or base reacts with achemical indicator. One of the best known indicators is litmus, a mix-ture of plant compounds extracted from certain lichens. This pinkishmixture turns red when in contact with an acid and blue when it contacts a base. Small strips of paper soaked in litmus are a standarddiagnostic tool for chemistry.

acidic

0 1 2 3 4 5 6

normalrain5.6

milk6.6

batteryacid0.5

lemonjuice2.0

apples3.0

vinegar 2.2

tomatoes4.2

198 MHR • Environmental Chemistry

Some people like awedge of lemon withtheir fish. Others preferto sprinkle vinegar. Did you know that both ofthese are examples ofneutralizing reactions?Fish contain a com-pound that is basic, sothe acid in lemon juiceor vinegar neutralizesthe base. It may soundfishy, but it’s true!

The “power” reported as pH is actually a power of ten inscientific notation. Take a strong acid, with pH 0.0, as astarting point. An acid with pH 1.0 has one tenth, or 10–1

times, the concentration. Vinegar, with pH 3.0, has onlyone thousandth, or 10–3 times, the concentration. Howmany times lower is the concentration of rainwater?

pH: A Powerful ScaleWhile litmus turns red in acid solutions andblue in basic solutions, it gives only anapproximate idea of how acidic or basic asubstance is. A more exact reading requiressome technology.

The strength or concentration of an acidor base determines the extent to which itreacts with water. This reaction changes theelectrical conductivity of the water, whichcan be measured with a sensitive meter, asshown in Figure 3.8. The pH scale is a wayof comparing the relative acidity or alkalini-ty of a substance. In later courses, you willlearn more about the criteria for measuringacidity and alkalinity and the exact chemicalchanges that occur when an acid or basereacts with water.

As shown in Figure 3.9, a pH of 7 indi-cates a solution that is neither acidic norbasic. It is neutral. If the pH of a substanceregisters below 7, the solution is acidic.Above 7, it is basic. There are a number of indicator substances thatturn different colours depending on the pH of the solution. Universalindicator (containing many such indicators) or pH paper will changeto a colour that is characteristic of a specific pH. These colours arethen matched against a chart that shows the range of colours for knownpH values.


Figure 3.8 There areseveral ways to determinethe pH of a substance. ApH meter and pH paper aretwo ways shown here.

basic

7 8 9 10 11 12 13 14

humanblood

7.4

normalGreat Lakes

water8.5

ammonia11.1

draincleaner

14.0bakingsoda8.2

milk ofmagnesia

10.5

neutral

Figure 3.9 This diagram shows the pH of some common substances. Approximately how much more acidic is lemon juice than drain cleaner?


Find OutWhat Is the pH of Your Rain?In this activity you will investigate the pHof some common acids and bases.

Materials

plastic containerrainwater (or melted snow)pH paper, indicators, or pH meter

Procedure

1. Decide which method you can use to testthe pH of rain or snow.

2. During the next rainfall or snowfall, usethe plastic container to collect a sampleof the rainwater or snow. If you collectsnow, let it melt.

3. Use an appropriate method to determinethe pH of your sample.

4. Compare your results with your class-mates’ results.

What Did You Find Out?

1. How did the pH value you obtained com-pare with your classmates’ pH values?Account for any large discrepancies.

2. Calculate the average pH of the samplesobtained by your class. Is this value whatyou might expect for your area? Why orwhy not?

Performing and Recording

Analyzing and Interpreting

In Danish, the “p” of pH stands for portenz meaning“strength.” In German, the word for “power” is potenz.Both of these words come from the Latin potens. Whichwords in English are related to the Latin word potens?

The word “pH” means the “power of hydrogen” and refersto the formation of hydrogen atoms that have lost anelectron. Each pH unit on the pH scale stands for a ten-fold increase in acidity or alkalinity. For example, a pH of5.3 is ten times more acidic than a pH of 6.3, and a pH of4.7 is 100 times more acidic than a pH of 6.7.

Some commonacids and bases

The pH of Common Acids and BasesMany common substances are either acidic or basic. In this investigation, you will make your own indicator and use it to find the pH of some common substances.

QuestionWhat is the pH of a carbonated drink, and other common solutions?

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S K I L L C H E C K

Initiating and Planning



Communication and Teamwork

Procedure Take two leaves from a redcabbage. Tear them intopieces about the size of apostage stamp. Put the piecesinto a plastic container.

Ask your teacher to pourabout 40 mL of hot waterfrom a kettle into the con-tainer. Carefully seal thecontainer, and leave it onyour table to cool until itcan be handled safely. Whilethe water is cooling, com-plete step 3.

Copy the table below intoyour notebook. You will needenough space to record yourobservations for nine solu-tions. Also make a pH dia-gram similar to Figure 3.9.You will fill in substances asyou determine their pH.

When the water in the con-tainer has cooled enough foryou to handle the containersafely, use the potato masherto mash its contents. Keepdoing this until the liquid isdeep blue or purple.

Part 1

The Cabbage TestSafety Precautions

• Ammonia is corrosive and toxic.Inform your teacher if youaccidentally spill ammonia.

• If you spill any of the solution onyour skin, immediately wash thearea with cool water.

Apparatusplastic container with a tight lidpotato masher, spoon, or forkuniversal pH papertest tubes and a test tube rack100 mL beakerglass stirring rodmedicine dropperpH meter (for teacher use)kettle (for teacher use)

Materials2 red cabbage leaves

Solutions to Test (10 mL each)lemon juicevinegarrainwaterdistilled waterblack coffee liquid soap or shampoomilk of magnesiahousehold ammoniaclub soda (leave to last)

Solution Colour of cabbage indicator Approximate pH range

lemon juice

CONTINUED

Open the container, andcarefully pour the liquid intoa 100 mL beaker. Discardthe cabbage leaves as directed by your teacher.

Pour about 10 mL of lemonjuice into a test tube. Use aclean glass stirring rod totransfer a drop of the juiceto a piece of universal indi-cator paper. Compare thecolour with the colours inthe chart. Estimate the pHof lemon juice, and record itin your table. Write “lemonjuice” above the correspond-ing pH on your diagram.Rinse the stirring rod withwater, and dry it with apaper towel.

Use the medicine dropper toadd a few drops of cabbagejuice indicator to the lemonjuice. Record the colour ofthe indicator beneath thepH you estimated for thelemon juice.

Repeat steps 6 and 7 foreach of the other solutions,except the club soda. About20 mL of cabbage juice indi-cator should be left for step9 and Part 2.

Pour about 10 mL of clubsoda into a test tube. Usingonly your observations ofthe colours of the cabbagejuice indicator, estimate thepH of the club soda. Enteryour observations for clubsoda in your table.

Set aside the cabbage juiceindicator for Part 2. All other solutions can be rinseddown the sink with plenty of water. Discard indicatorpaper as directed. Wash your hands.

TeacherDemonstration

Although pH meters aremore accurate than indicatorpaper, they are relativelyexpensive and require largervolumes of liquid. For thesereasons, your teacher maydemonstrate how a pH meteris used to measure the pH ofthe solutions you tested.

Part 2

Breath CheckYou will use your indicator toanalyze your breath. Doesbreath produce an acidic, basic,or neutral solution in water?

Safety Precautions• If you spill any of the solution on

your skin, wash the areaimmediately with cool water.

Apparatusclean plastic straw250 mL beakermedicine dropperstirring rod

Materialscabbage juice indicator from Part 1100 mL distilled water5 mL household ammonia20 mL vinegar


You can make your own indicator to test for acids and bases.

ProcedurePour about 100 mL of dis-tilled water into the 250 mLbeaker. Use the medicinedropper to add two drops ofhousehold ammonia to thewater. Stir the solution.Rinse the medicine dropperwith distilled water.

Drop by drop, add justenough of the dilute ammo-nia solution from step 1 tothe cabbage juice indicator tochange the colour from deepblue or purple to pale green.

Using a clean plastic straw,carefully and gently blow asteady stream of bubblesthrough the indicator solu-tion. Continue blowing untilyou observe a change.Remove, rinse, and discardthe straw. Describe thechange in your notebook.

Pour a little vinegar into thesolution from step 2, untilthe colour changes. Recordthe new colour. Pour yoursolutions down the sink, andrinse with plenty of water.Wash your hands.


The straw is used to gently blowbubbles through the indicator. Whenfinished, the student will rinse anddiscard the straw.

Analyze1. List the solutions you tested from most acidic to most basic.

Compare your list with the lists of other classmates.

Conclude and Apply2. Which is more acidic, club soda, or a cola drink with a pH of

about 3.0? Check the labels on containers for both drinks,and find an ingredient that might account for the difference.

3. Did the gas in exhaled breath dissolve in water to produce asolution that is acidic, basic, or neutral? Summarize the evi-dence that supports your conclusion. Which gas in exhaledbreath caused the change?

Since soils in different environments have different natural pH values, theplants that grow there have evolved to suit the pH ranges they must growand live in. For example, rhododendrons flourish in moist, acidic environ-ments and grow best at a pH of about 5. Many grasses, including wheat andmaize, grow in drier environments, where they must tolerate a pH of 7 or 8.(What can you determine about the “natural” pH of rainwater from this?)

Gardeners and farmers can adjust the pH balance to suit the plants and cropsthey want to grow. Clay soils are harder to “fix” than sandy soils, for exam-ple. Lime (calcium carbonate) or dolomitic lime (which also contains magne-sium carbonate) can be added to acidic soils, while ferrous sulfate or alu-minum sulfate can help correct soil that is too alkaline.

Why do you think these substances can change the pH of a soil? Work outbalanced chemical equations for reactions when (a) calcium carbonate isadded to soil with excess nitric acid and (b) aluminum sulfate reacts with thewater in an alkaline soil. Why are sodium hydroxide and sulfuric acid neverused to adjust the pH of soil?

Acid Precipitation—a Global ConcernOver the past 30 years, there have been few issues that have createdmore studies, debate, or controversy than acid precipitation. Thechemistry behind acid precipitation is clear. Oxides of carbon, nitrogen,and sulfur produced by burning organic materials react with moisturein the air to form acids. The process is illustrated below.

In a process called acid precipitation, these acid compounds are washedout of the air by rain and snow and may be deposited a long way from thesource of the oxides. Acid rain or snow looks, feels, and even tastes normal,but this rain or snow causes an estimated $1 billion in damage each year.

Acid damages and, in some cases, destroys aquatic ecosystems oflakes and streams, reduces productivity of crops, harms other vegetation,and accelerates the decay of our buildings, structures, and monuments.Acid corrosion is such a problem in Italy that some famous marble statues have had transparent cases filled with inert gases erected aroundthem to prevent further damage. In Canada, the loss in productivity foragriculture, forestry, and fisheries means fewer jobs and lower profits.Corrosion and erosion of structural materials requires expensive maintenance and repairs to our buildings, bridges, and machinery.


Acid precipitation in onecountry can be caused byemissions from anothercountry. In fact, more than50 percent of the acid pre-cipitation affecting easternCanada is due to oxidesoriginating in the UnitedStates. This has been anissue in political discussionsbetween Canada and the United States since the 1970s.

SO2(g) + H2O(�) → H2SO3(aq)

SO3(g) + H2O(�) → H2SO4(aq)

2NO2(g) + H2O(�) → HNO2(aq) + HNO3(aq)

CO2(g) + H2O(�) → H2CO3(aq)

sulfurous acid➤

carbonic acid➤

sulfuric acid➤nitrous acid and nitric acid➤

Figure 3.10 Sulfuric and nitric acids formed in the air by burning fossil fuels and otherindustrial activities threaten crops, water quality, building materials, and living organisms.

In 2001, David Schindler, aninternationally recognizedecologist at the Univeristy ofAlberta won one of thelargest science prizes on thecontinent. His research onacid precipitation and theimpact of phosphorus-baseddetergents on the world’sfreshwater supplies nettedhim the $1-million GerhardHerzberg Canada Gold Medalfor Science and Engineering.


Toxic Substances OfficerLori Forster-Clegg loved animals while grow-ing up. She also loved biology. Lori broughtthose passions together with a diploma in bio-logical sciences and pollution technology andthen a Bachelor of Science in biology. Duringthe summers she banded ducks, gatheredinformation about spills, created pamphlets,and researched toxic substances. Now Lori isa toxic substances officer with EnvironmentCanada’s prairie and northern region —Alberta, Saskatchewan, Manitoba, NorthwestTerritories, and Nunavut — from her Edmonton office.

Lori’s job involves being on the lookout for banned substancesentering Canada, focussing mostly on ozone-depleting sub-stances and substances new to Canada. Industries contact herto see if materials they want to import are regulated or illegal.New substances that aren’t on the approved list need to betested. The industry that is trying to import a substance con-ducts environmental and toxicity tests on the substance. Theythen submit these results to Environment Canada’s headquar-ters in Ottawa. Lori helps industries put together their submis-sion package and helps them understand the rules so they canmore easily follow them.

Inspectors, ensuring that the environ-mental laws are being followed, alsocontact Lori about whether certain sub-stances are banned. They look to her foranswers and training. “I’m in a positionto know the science behind the regula-tions — why they’re in place — andhow they benefit the environment,” shesays. Lori explains the environmentalregulations so inspectors know what tolook for when they are on-site. While shespends most of her time at her desk on

her computer, inspectors often ask Lori to come along oncalls because they are not familiar with the hundreds of dif-ferent chemicals.

Does Lori’s job sound interesting to you?

• Conduct some research over the Internet or at the libraryto find out more about what it takes to become a toxicsubstances officer.

• What level of education does it require?

• Which volunteer opportunities will give you experience inthe field while you’re still in school?

International AgreementsIn 1996, in response to the public’s concern about increasing damage tothe environment, Canada and the United States agreed to reduceindustrial exhaust emissions by 10 percent by the year 2000. In addi-tion, exhaust emissions from cars built before 1998 were to be reducedby 60 percent. As a result of these pollution control measures, levels ofsulfur and nitrogen oxides in the environment are diminishing.

There has been much disagreement over exactly howacid precipitation affects living organisms. After all, itlooks, feels, and tastes normal. What is it about acid pre-cipitation that causes damage? For terrestrial ecosystems,one major effect is that acid added to the soil dissolvesmineral nutrients and allows them to be leached or washedaway, resulting in nutrient-poor soil and poorer growingconditions for plants. In certain areas leaching may alsofree heavy metals to wash into streams and water supplies,where they may then be consumed by plants and animals.Heavy metals are those with a density of over 4.0 g/mLsuch as lead, mercury, cadmium, and nickel. These metalsare deadly to most organisms. You will learn more abouttheir effects in later Topics.

Figure 3.11 These maple leaves show damageby acid precipitation.

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QuestionHow do variations in pH affectthe growth of yeast?

Safety Precautions

• Handle the hot plate with care toavoid burns.

• Handle the microscope slideswith care.

• If you spill any of the solutions onyour skin, wash the area withplenty of cool water.

Apparatusmicroscope 7 test tubesmicroscope slides thermometercover slips 100 mL beaker100 mL graduated hot plate

cylinder marker

Materialsyeast culturewaterdilute acid solution dilute base solution sugarlabels

ProcedureWork in a small group.Measure 100 mL of water intothe beaker. Place the beakeron the hot place, and bringthe water temperature to30°C. CAUTION: Handlethe hot plate with care.

Add 3 g of sugar and 0.5 gof yeast. Stir well.

Prepare seven test tubeswith a pH range of 2 to 8.Label each test tube.

Add 10 mL of yeast cultureto each test tube. Allow thetest tubes to sit for 24 h.

Devise a sampling techniqueto estimate the relative

population density of yeast ineach test tube. Examine eachsample under the micro-scope. Record your results.

Make a graph that shows therelationship between popula-tion density and pH.

Wash your hands after com-pleting this investigation.

Analyze1. At what pH did the yeast population show the most growth?

At what pH did it show the least growth?

Conclude and Apply2. The graph shows changes in the populations of various

aquatic organisms in Canadian lakes and rivers in relation topH levels. Study the graph, and answer the questions.

(a) Which organisms appear to be most sensitive to acidconditions? Which are least sensitive?

(b) Why might the population of a species of fish that is tol-erant of high acid levels still decline in an acidified lake?

(c) “When fish start dying, the damage has already been done.”From the information on the graph, explain why you agreeor disagree with thisstatement. Whichspecies might be bet-ter used as an earlywarning of acid dam-age in lakes?

3. From your results, andthe data presented, makea general statement aboutthe effects of acid precip-itation on organisms.

Fishes

pH7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5

0

100

Amphibians

0

100

Algae

0

100

Zooplankton

0

100

Aquatic insects

0

100

Per

cent

sur

viva

l

The Effect of pH on a PopulationIn this investigation, you will examine the effects of acid precipitation by observing the effects of pH on the growth of a yeast culture.

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S K I L L C H E C K





yeast cells

Using Chemistry to Control Acid EffectsAcid precipitation falls all across Canada, but someareas are affected more than others. Believe it or not,the same chemical reaction that is destroying the marbletablet in Figure 3.12 is exactly the same reaction thatprotects areas of western Canada from acid precipita-tion. Study the chemical equation that accompaniesFigure 3.12. Did you notice that the products of thereaction of calcium carbonate and sulfuric acid are notacidic?

During the last ice age (about 20 000 years ago), glac-iers covered much of North America. As the glaciersadvanced, they eroded the rocks over which they passed,carrying the debris with them. When the glaciers melt-ed at the end of the ice age, the crushed rocks were leftbehind. In western Canada, the rock debris contained asubstantial amount of alkaline minerals such as calciumcarbonate or calcite. This calcium carbonate lying at thebottoms of lakes in the Canadian west neutralizes theacids entering these lakes.

This presents us with a chemical solution to theproblem of acidified lakes. Add a quantity of powderedcalcium carbonate to the lake in question and voilà —instant neutral water. One major source of calcium carbonate is limestone; the process of adding calciumcarbonate to the environment is referred to as liming,as shown in Figure 3.13. The correct term for such achemical reaction is an acid-base neutralization.

You might be wondering why we aren’t neutralizingthe effects of acid precipitation in all the acidifiedlakes if it is so easy. You will find out why after thenext investigation.


Figure 3.12 Many monuments and statues — somethousands of years old — are made of marble andlimestone. These substances contain calciumcarbonate (CaC03), which is easily decomposed bysulfuric acid:

CaC03(s) � H2S04(aq) → CaS04(s) � H20(�) � C02(g)

Calcium sulfate dissolves in water more readily thancalcium carbonate. Thus the monuments and statuescorrode as the calcium sulfate is washed away.

Normal rainwater has a pH as low as 5.6 due to the carbonic acidformed as carbon dioxide gas dissolves into the water. The presenceof sulfur oxides and nitrogen oxides from industry and transporta-

tion in the atmosphere results in rain that is even more acidic. Central Europe, Japan, andeastern North America are severely affected by acid precipitation. In these areas, rainwater canhave an acidity approaching that of vinegar (pH 3.0), which is about 1000 times more acidicthan normal rainwater. Amazingly, there are even more extreme acid conditions. In 1974 astorm dropped rain with a pH of 2.4 over Scotland, and fog over Los Angeles has been measured with a pH as low as 1.7! This is 10 000 times more acidic than normal.

Figure 3.13 Liming is done by releasingpowdered calcium carbonate from aircraft.


Drop-by-DropNeutralizationAs you know from Unit 2, when acids and bases neutralize each other, theproducts are water and a “salt” compound. Regardless of the strength ofthe acid or base, neutralization will occur, even though the amounts of acidand base may not be equal. A relatively weak acid or base can be used toneutralize spills of much stronger acid or base. An antacid is a good exam-ple. Acid in your stomach that helps digest your food has a pH of about 2.“Heartburn” occurs when acid from your stomach enters your esophagus.It is relieved by swallowing an antacid, which is just a weak base.

QuestionHow does an antacid comparewith baking soda and a strongbase in neutralizing an acid?

PredictionMake a prediction aboutwhether an antacid, baking soda,or a strong base will be mosteffective in neutralizing acid.

Safety Precautions

• This investigation uses caustic,corrosive substances. Clean upany spills carefully and informyour teacher.

• Bromothymol blue is flammable.Keep it well away from flames.

Apparatus3 100 mL beakers or 3 petri dishes2 medicine droppers or 1 mL

micro-pipettesstirring rodbalance

Materialsdropper bottle of bromothymol blueindicatordilute sodium hydroxide, NaOH (aq)dilute hydrochloric acid, HCl (aq) (Note: These two solutions shouldhave the same concentration)waterantacid tabletbaking soda

ProcedurePlace a few drops of bro-mothymol blue indicator ina small, clean beaker or petridish. Then add 2 mL ofsodium hydroxide solution.

While stirring the solutionwith the stirring rod, addhydrochloric acid slowly,counting the drops untilthe colour of the indicatorjust changes, and thecolour change lasts at least20 s. Record the number

of drops and appearance ofthe solution.

Dissolve 2 g of baking sodainto 2 mL of water. Repeatsteps 1 and 2, using the bakingsoda solution in place of thesodium hydroxide solution.

Plan the steps you will take tocompare the antacid tablet tothe sodium hydroxide andbaking soda solutions. (Hint:Break the tablet into pieces.)

Remove your gloves andwash your hands.

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S K I L L C H E C K





Analyze1. Compare your results (the

number of drops added in thethree neutralization reactions)with your classmates’ results.Discuss any differences.

2. Using the number of drops ofhydrochloric acid needed toneutralize the antacid tabletand baking soda, calculate themass of baking soda equal toone antacid tablet.

Conclude and Apply

3. What would happen if morebaking soda were added afterneutralization occurred?What colour would the indi-cator turn? Why?

4. What would be the danger in swallowing many antacidtablets?

5. Which base was most effec-tive in neutralizing acid?How does the “alkalinity” ofantacid compare to sodiumhydroxide solution?

Using Chemistry to Control Harmful EmissionsYou have observed how alkaline substances react with acids in a neu-tralizing reaction. So why not use this process to eliminate the problemof acidified lakes?

Liming has been used, but with limited success. Rivers and streamsconstantly feed acidified water into lakes, so the lakes would have to belimed continually to keep up with the new influx of acid. Imagine thecost of treating between 14 000 and 150 000 affected lakes! Do youthink the cost would outweigh the benefits, or vice versa?

Since it is impractical and expensive to neutralize all of the acid pre-cipitation we humans are causing, the only other option is to reduce oreliminate the oxides. How can this be done? Chemistry to the rescue!

Chemical engineers use their knowledge of chemistry to design andbuild devices to remove oxides before they get into the air. Catalyticconverters, such as the one shown in Figure 3.14, are required onmost vehicles and are a good first step.

Catalytic converters contain a ceramic or wire honeycomb-like struc-ture coated with a thin layer of metallic catalysts, such as platinum,rhodium, and palladium. A catalyst is a substance that speeds up achemical reaction without being used up in the reaction. The large surface area of the honeycomb structure helps produce a completecombustion. A converter aids the formation of carbon dioxide andwater from hydrocarbons, reducing the amounts of carbon monoxideand nitrogen oxides produced. The purpose of the converter is toencourage complete oxidation.


Figure 3.14 While catalytic converters are quite efficient, they work bestwhen the catalysts are warmed up. It takes about 90 s, after a car starts,for the catalysts to be activated. Unfortunately, it is during this brief warm-up that the car produces about 70 percent of all the pollutants that itreleases during its driving cycle.

You might expect the pH of a lake to decreasegradually as acid water enters. However, thisgradual decrease does not happen in a lake witha limestone bed. Such lakes are common inSouthern Ontario, Southern Québec, and theAtlantic Provinces, but not on the CanadianShield or the Prairies. Some lakes in the RockyMountains also have limestone beds. Calciumcarbonate in the limestone bed of a lake reactswith acids, and so the pH stays fairly constant asacid water enters the lake. But when all of thelimestone has reacted, the pH suddenly drops.The rapid change in pH is deadly to the ecologyof this type of lake.


Figure 3.16 These little beadspack a big punch by removingsulfur dioxide and nitrogenoxides — pollutants responsible for acidprecipitation — from gas givenoff during coal combustion.

CaCO3 tosmokestack

scrubber

furnace wet slurryof CaSO3

coal (C+S)

air

CO2 + SO2

CO2 + CaOSO2 + CaO

O2 CO2

CO2

CaSO3

water + CaO

Scrub Those Cares AwayThe oxide emissions from industrial factories and power plants thatburn coal can be a major source of oxides depending on the sulfur con-tent of the coal being used. The installation of “scrubbers” (devicesthat use a sorbent — a substance that can adsorb, or capture oxides) isa good way to reduce oxide emissions.

Traditional “wet” scrubbers remove sulfur dioxide gas (SO2(g)) byreacting heated gases with calcium oxide or lime (CaO). Figure 3.15illustrates this process. The calcium oxide sorbent is used up in thisreaction and the waste calcium sulfite (CaSO3) is disposed of. A largepower plant might produce millions of tonnes of waste calcium sulfiteevery year, most of which presently ends up in landfills.

Newer scrubber technologies have the potential to be more effective,environmentally friendly, and economical. The use of metal oxide sorbents(as shown in Figure 3.16) is the key. One such system, COBRA (copperoxide bed regenerable application), uses a sorbent of small beads of alu-minum oxide impregnated with copper. The beads form clusters of copperoxide on their surface and as heated gases pass by, SO2(g) reacts with thecopper oxide to form copper sulfate. Fresh beads are continuously addedand “spent” beads are removed. The spent beads are then treated withmethane gas to release theSO2(g) and restore thebead to its originalstate for reuse.Meanwhile thetrapped SO2(g)can be treated toproduce elementalsulfur, sulfuric acid,or even ammoniumsulfate fertilizer.

Figure 3.15 The key to “scrubbing” exhaust gases is the addition of calcium oxide (Ca0), which reacts with thesulfur dioxide gas (S02) to form calcium sulfite (CaS03). The calcium sulfite can be washed away with water.

www.mcgrawhill.ca/links/sciencefocus9

During the formation of coal, large amounts of methane-richgas are created and remain trapped within coal beds and the sur-

rounding rocks. Mining of coal beds will allow this methane to escape intothe atmosphere where it acts as a potent greenhouse gas. Find out how

“Clean Coal Technology” may turn this problem into a profit — both eco-nomic and environmental! Go to the web site above, and click on

Web Links to find out where to go next. Design an adver-tising logo, jingle, or print ad to sell this

new technology.

Look up the words“absorb” and “adsorb” inyour dictionary. Explain thedifference between them in your notebook.

All of these products have applications we can make use of! As abonus, the addition of ammonia to the heated gases triggers a catalyticreaction that breaks down nitrogen oxides into nitrogen and oxygen gasand water vapour.

In tests, COBRA removed all nitrogen oxides and 95 percent of the sul-fur dioxide from emissions. This is comparable to or better than the resultsobtained by traditional scrubbers without the landfill waste. The copperoxide sorbent is more expensive to produce than sorbents in traditionalscrubbers. However, since it is reusable, costs are recovered over time. Aswell, there is an end product to sell instead of waste to throw away.

Finally, what about the small amounts of oxide gases that make itpast these devices? How much of a problem do they pose? What aboutthe mountains of waste calcium sulfate produced by traditional scrub-bers every year? Are they a problem? Both are pollutants, but how dothey compare? You will explore this question in Topics 5 and 6.

1. Which human activity is the major cause of acid precipitation?

2. Which key property do all indicators possess?

3. It is thought that pain results from a change in the pH of the fluid thatsurrounds nerve cells. The fluid within your cells is slightly acidic, so acut or burn releases this fluid and causes pain signals from your nerveendings. What would you expect to find if you tested the pH of creamsand lotions used to treat cuts and burns?

4. Suppose you have two containers, one containing a dilute acid and theother a dilute base, but there are no labels on them. Describe how youcould use red cabbage to determine which solution is which.

5. Hydrofluoric acid, HF(aq), reacts with sodium hydroxide, NaOH(aq), toform a compound that is used in toothpaste to prevent cavities. What isthe name of this compound?

6. Apply Coffee makers and kettles eventu-ally become clogged with a buildup of“scale” from deposits of calcium carbonateand magnesium carbonate. Explain howpouring vinegar into your coffee maker orkettle removes this scale.

7. Thinking Critically Give three reasons why eastern Canada is moreaffected by acid precipitation than western Canada. How might increasedacidity levels affect the economy of eastern Canada? Consider tourism,factories, and taxes.


T O P I C 3 Review

Fossil fuels such as coal, oilor natural gas are the sedi-mentary remains of swampvegetation. Burning fossilfuels releases solar energy,which was stored in plantmatter through the process ofphotosynthesis millions ofyears ago. Intense heat andpressure exerted on the plantmatter initially forms bitumi-nous (soft) coal. Higher pres-sures and temperaturechange bituminous coal tothe harder anthracite coal.Alberta contains 70 percentof Canada’s coal reserves,mostly of the sub-bituminouscategory. Approximately four-fifths of the coal produced inAlberta is used as fuel for thegeneration of electricity.Alberta coal is low in sulfurand burns cleaner than mostcoal found in other areas ofthe world.


T O P I C S 1 – 3Wrap-up

If you need to check an item, Topic numbers are provided below.

Key Termsnutrientmacromineraltrace elementenzymevitaminproteinlipidcarbohydrate

biological magnificationbiomagnificationherbicideinsecticidefungicidepesticideacidicbasic

acidbaseacid precipitationindicatorlitmusoxidationpH scalepH paper

acid-base neutralizationleachheavy metallimingcatalystcatalytic converterscrubber

Reviewing Key Terms1. In your notebook, write the description in

column A beside the correct term in column B.

A B

• a naturally occurring • pH scale (3)catalyst found in cells

• the reaction of an acid and • trace element (1)base to form a salt and water

• process where chemicals • acid precipitation collect in the tissues of (3)organisms, increasing in concentration toward the top of a food chain

• a chemical substance that • enzyme (1)changes colour in response to changes in acidity or alkalinity

• a mineral needed in • catalyst (3)amounts less than 100 mg per day

• a substance that speeds • biological up a chemical reaction magnification (2)but is not depleted or changed by the reaction

• a scale that measures • acid-basethe relative acidity or neutralization (3)alkalinity of a substance

• rain or snow that contains • poison (2)high levels of acid

• a substance that causes • indicator (3)illness or death when it enters the body in food or drink

Understanding Key Concepts2. Modern food processing and refining used in

the packaging of food products decreases themagnesium and potassium contained in thosefoods. Name some of the likely symptomsshown by a person eating only refined foods. (1)

3. What is the role of an enzyme in your body? (1)

4. What are the characteristics of DDT (andother “chlorinated” hydrocarbon pesticides)that make it both a valuable pesticide and anenvironmental problem? (2)

5. The figure below shows a field planted withhybrid wheat called triticale. It is richer in pro-tein than wheat and is used for human food andlivestock feed. List two risks and two benefits ofplanting only one crop, such as triticale. (2)

6. List the characteristic properties of acids andbases. (3)

7. Your brother has eaten too many doughnuts,and now he has acid indigestion. He cannotfind a commercial antacid product. Could heuse baking soda? Explain why or why not. (3)

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TOPIC 13 How Do You Spell Relief? 1 Ahh! After a hard day mowing the lawn or raking leaves, there isn’t anything better than the clean, refreshing taste of your favourite soft drink,