CHEMISTRY/PART 4

ACTIVITY 2 The Cartesian Diver

Purpose stretcha rubber ballon over the mouth of each con- Toinvestigate how salinity and pressure affect lainer and secure it with a rubber band. densityand how this affects objects floating in water. Pressthe sidesof thetwo-liter bottle containing the freshvvater. In the caseof the othercontainers, EquipmentINIaterials pressdown on the rubbercover. What happens to the drop peP *2 plastictwo-liter soda containers, 2 large test tubes Releasethe pressureon the bottle or rubber 0 x 3.5cm!, 2 graduatedcylinders 00 mlor cover.What happens to the dropper? larger! or 2 glassjars Whathappens to theamount of waterin the drop- 2 identicalmedicine droppers Cartesian Divers! per/testtube as it submerges? salt Now press on the sides or rubber cover of the teaspoon saltwatercontainer. Does the medicinedropper plastic funnel behavedifferently in the salty water?

'If largetest tubes, graduated cylinders or jars are Questions used,two piecesof thin rubber ballons!and two rub- ber bands are needed. t. Doesthe CartesianDiver submerge easier in fresh or salt water? Procedure 2. Does the Cartesian Diver nseto the surfacefaster in Fill each of the selectedcontainers almost full of fresh or salt water? water.Use the plasticfunnel to add 4 to8 teaspoons of saltto oneof the containers. Larger amounts of salt 3. What makes the CartesianDiver dive? shouldbe addedto the largercontainers.! Shake the containerto help the salt dissolve. 4. Why does the CartesianDiver rise back to the sur- Suspenda medicinedropper vertically in eachof face of the water? thecontainers. They can be suspendedwith a few drops of water in them, 5, Discussthe relationshipamong density, salinity and If you are using the two-literbottles, screw the pressure. caps on. If you are using any of the other containers,

C/45 CHEMISTRY/PART 4

ACTIViTY 3 ScubaDiving and the Gas Laws

introduction to Gas Laws Tointroduce the gas laws in the context of scuba Boyfe's Law dtvlrlg. Boyle'slaw statesthat at a constanttemperature, the volumeof a gas will vary inverselywith pressure, Background while the density of the gas varies directlywith the Peoplecan explore the marine world by using a pressure. mask,snorkel and fins and holding their breath. Qr This means that as the pressure on a volume of theycan prolong their exploration with the use of gas doublesthe gas is compressedto one-halfits scuba selfcontained underwater breathing appa- volume see Figure 2!. If the pressuretriples then the volumeis compressedto equal one-thirdof its original ratus! equipment, Theself-contained breathing apparatus consists volume. ofa tankfilled with compressed air,a regulatorwith a mouthpieceand a BCD Buoyancy Control Device! Figure1!, Figure 2 Boyle'slaw pressure Volume Density Lungs of a diver Depth on lungs of air of air holdingbreath Figure1 Self-containedbreathing apparatus 0 feet 1.0 atm 40 liters 1 kg/f

BCD

33 feet 2.0 atm 2 0 liters 2 kg/1 /2!

regutator

A regulatorreduces the high pressure ofthe air in 66 feet 3.0 atm 4/3 liters 3 kg/1 a scubatank to a usablelevel and deliversair when neededby the diver,A BCDis mandatoryequipment for all diving.It is an irrllatablesack that increases buoyancy.It is usedto providesurface support to rest, swimand maintainneutral buoyancy under water. Othertypes of divingequipment are available but are lessaccessible to the generalpublic. Scubadiving has become a popularhobby for 99 feet 4.0 atm 10 liter 4 kg/1 manypeople. It offersa wealthof informationon div- /4! ing physiologyand the effectsof gas exchange.

C/46 CHEMISTRY/PART 4

Oneof the first effects a diverfeels is increasing blockshis nose and attempts to exhalethrough rtwith pressure.As he descends,the pressurearound him hismouth closed. This forces air into the air spaces in- increasesby 1 atmospherefor every33 feetof de- sidethe ears and sinuses and relieves the squeeze. scentin saltwater 4 feetin freshwater! Figure 2!. Thistechnique isknown as equalizing. Theincreasing pressure is notfelt by boneand solid Theprocess of equalizingreturns the air spaces tissuebut by air spaces ears, lungs and sinuses! to theirnormal volume by equalizingthe external Figure3!. waterpressure and the pressurein the air spaces,As longas a diverbreathes compressed airand equalizes the pressurein the air spaces,he will notfeel the Figurie3 Air spaces in the body squeezing as he descends.

Figure4 Techniqueto relievepressure on theear drum

airw nasal c middle ear

ngs

stomach

intestines

Whena diverdescends, the increase in pressure reducesthe size of hisair spaces Figure 2! andcom- A diverascending experiences the opposite pressesthe air inside.A diver who holds his breath pressure-volumerelationship. The pressuredecreases feefsthe increase in pressure decrease in volume! as andthe volumeincreases. A divernot breathingon a squeezingin his lungs, sinuses and ears Figure 4!. ascentwill feel his lungs expand Figure 5!. A diver's Asthe pressure increases, the squeezing increases lungscan only expand 15 to 30percent of theirorig- andbecomes uncomfortable. Eventually the diver will inalvolume without bursting. Therefore, ascending stop his descent. withoutbreathing may result in lung tissue bursting Torelieve the pressureon the lungs,a diver Figure 5!. breathescompressed airat a regularfrequency. To relievethe pressure on earsand sinuses, a diver

C/47 CHEMISTRY/PART 4

Figuris5Lungs ofascending scuba diver ascending scuba diver ascendingscuba diver breathing constantly holding breath surface

RUPTUREi

33 feet

expanding air

66 feet

compressedair

99 feet

temperaturesdecrease thetemperature ofthe gas in A smartdiver breathes onascent. Breathing thetank and 'the gas decreases involume. resultsinequalizing thepressure inside the lungs and Consequently,thetank will not have as much air airspaces withthe outside pressure sothat the normal init asexpected. This will shorten the dive time. To lungand air space volume ismaintained Figure5!, avoidthis problem, dive shops place the tanks incool Asthe pressure increases, thedensity ofthe gas waterduring filling so maximum airvolume isachieved. increasesdirectly. This means that if thepressure ona gasdoubles, thedensity doubles. Asthe pressure of thegas increases, remember thevolume decreases Dalton's Law Thisdecrease involume results inthe gas rnolecules Dalton'slaw states that the total pressure exerted occupyinga smaller space. This decrease inspace bya mixtureofgases isequal tothe sum of the occupiedbya setnumber ofgas molecules means pressuresofeach of the different gases making up thatthe density increases. Anincrease inthe density themixture each gas acting as if it alonewas pres- ofair makes it more difficult tobreathe atdeeper ent and occupiedthe totalvolume. depthsthan at thesurface Thislaw is illustrated inFigure 6, which shows air tanksfilled under three different conditions. Charles' Law Condition A Charles''law states that if thepressure is kept con- Thetank contains only oxygen molecules ata low stant,the volume ofa gaswili vary directly with pressure.Ifthe total pressure ofthe gas is 160 mm of temperature. Thismeans that as the temperature ofa gasin- Hg mercury!andoxygen makes up 100 percent of creases,the volume of spaceit occupiesincreases. thegas, what isthe partial pressure ofoxygen? Thisphenomenon isseen in a diver'scompressed air answer:160 mm! tank.Filling the tank warms the air and causes it to A diver'scompressed airtank is neverfilled with pureoxygen because it is toxic When using pure oxy- occupya greater volume, Under water, the cooler gen,the blood's hemoglobin becomes saturated with C t 48 CHEMISTRY/PART 4

Condition C Figure 8 Dalton'slaw Thetank's total pressure has doubled to 1,520 condition A condition B condition C mmHg atm!.The percentage of oxygen and nitro- gen in the tankshas not changed.But more of both gaseshas been added to increasethe pressure. What isthe partial pressure of oxygenand nitrogen> Poz = P»,i x o%%dOz PNz- P~ x i%%dNz = 1520 rnm x 0,21 - 'I,520 x 0.79 = 320 rnm = 1,200 mm Thepercent of each gas in the total gas mixture does not change. But as pressureincreases, each of the partialpressures increase by the same amount. If you compare conditionsB and C, you will see that the totalpressure has doubled and so haveeach of the 160 rnm Hg 760 mm Hg 1520mm Hg partial pressures. total pressure total pressure total pressure NitrogenGas rrndWater Preesure- oxygen.This saturationturns off the reflexescontrol- Nitrogen Narcosis lingcarbon dioxide exhalation and allows it to buildup in thebody, This results in nausea,vomiting, dizziness, Theair you inhale is a mixtureof 78percent nitro- gen, 21 percentoxygen, 0,03 percent carbon dioxide tunne!vision, blackouts and grand mal seizures. andsmall amounts of othergases, The oxygen in the Condition B air you exhaledecreases from 21 to 16percent and thecarbon dioxide increases from 0.03 to 5.6percent. Nitrogenhas been added to the tankso that the Duringexhalation, the body produces roughly the totalpressure, Pr, is 760mm Hg atm!.No oxygen sameamount of carbon dioxide as the oxygentaken hasescaped so the Poz is unchanged.What is the in. Nitrogenremains the same PNz? At the surface,the pressureof air is one atm or 760mm Hg. Nitrogenmakes up 78percent of the air P»~- Poz+PNz witha partialpressure of about600 mm Hg. Asa diver 760 mrn =160 mrn+ PNz experiencesgreater pressures, the partialpressure of PNz-600 mm nitrogenincreases the percentage of nitrogenin air remainsthe samewith increasing pressure!. At greater Whatpercentage of the totalpressure is contributed than 100feet atm!,the increasein partialpressure by Oz? Nz? causes nitrogennarcosis. At depthsless than 100feet. nitrogenis not usedby the bodyand hasno effects 'VOOz- Poz / P~ on it. =60 mm/760mm! x 100 The symptomsof nitrogennarcosis are likethose = 21o%%dOz of intoxication.Divers act foolish,take off their masks, removetheir mouth piecesand descendpast safe O%%dNz- PNz/P~ limits.Several factors, including alcohol, a hangover, - 00 mm/760mm! x 100 fatigue,excess carbon dioxide, inexperience and anxi- = 790%%dNz ety lower a diver'sresistance to nitrogennarcosis. Nitrogenaffects divers differently; any one cliver may Thesepercentages are approximately thevalues experiencea vanetyof symptoms. foundin the air we breathe Dther gases such as Fordivers working at depthsgreater than 100 argon, neon and carbon dioxide are found in the at- feet,the compressedair mixtureis changed.Nitrogen mospherein verysmall quantities. Compressed air is removedand replaced with inert gases, usually tanksare filled with these same percentages ofoxygen helium.This removes the problemof nitrogennarcosis and nitrogen. and allowsthe diverto work deeper.But heliumis rare and costly.Usually only commercialand other profes- sionaldivers descend to depthsgreater than 100 feet

C /49 CHEMlSTRY/PART4

Nitrogenand Water Pressure The Bends Nitrogen,inair and compressed air,does not Henry'slawstates thatthe mass ofa gasdis- combinewith blood like oxygen Asa diverdescends solvedbya definitevolumeof liquid ata constanttem- nitrogengoes into solution inthe diver's blood and is peratureisdirectly proportional tothe pressure on that carriedtothe tissues and fat A diver'sbody tissues gas.Theequation expressing therelationship between balancewith the partial pressure ofnitrogen fora par ticulardepth ineight to12 hours. The saturation of solubilityand pressure is: tissuesbynitrogen increases withthe length ofthe Cg- kPg diveat a particulardepth and pressure,

Where: C,-solubility ofgas in the solution phase Figure8 Oxyqen extraction byair breathing animals k- proportionalityconstant P,= pressureofgas over the solution Thismeans thata 'liquidwillabsorb a gas from COp withinandoutside itself Figure 7!.For example, the surfacewatersof the ocean aresaturated withairat sealevel pressure atm!.A human's bloodis saturatedwithoxygen, nitrogen andother gases foundin air at sea level pressure.

Figure7 Henry's law Og 02 rich poo' OCEANSURFACE pressure- 1 atm

N2 N, bsorotic ri relea

tissues

HB = hernoglcbiir

~ windpipe Asa diverascends, 'thepartial pressure ofnitro- geninthe lungs decreases. Bloodleaving thelungs at lowerpress~re hasa lowernitrogen partial pressure andis circulated tobody tissues. Thetissues have a highernitrogen partial pressure sonitrogen escapes 'fromtissues intothe blood. The blood returns tothe lungswhere nitrogen diffuses intothe air exhaled Figure8!.With each round ofcirculation, morenitro. genisremoved. Nitrogen iseliminated fromsaturated bronchi tissuesin9 to12 hours This elimination processis LUNGS known as decompression.

C /50 CHEMISTRY/PART 4

If decompressionoccurs too rapidly,the blood and tissuesmay receivetoo much dissolvedgas to Fleure9 Areasaffected by decompressionsickness hold in solution.Because the load of gas cannot be carried to and eliminatedfrom the lungs quickly enough. the gas liberates itself in the form of bubbles that appear in the blood and tissues. Therefore, a diver needsto observecertai~ "hold points" during his as- cent. Stopping at certain points allows time for excess nitrogen to be removed from the bloodstream to the lungs. The classicexample of dissolvedgas coming out of solution is a bottle of soda. No bubbles are visible when the cap is on becausethe liquid is under pres- sure and the bubbles are too small to be seen. Re- rnovingthe cap reducesthe pressure.The bubbles come out of solution.When the partial pressureof the carbon dioxide gas dissolvedin the soda equalsthe partial pressureof the gas in the air surroundingthe li- quid, the soda does not bubble and is considered "flat." Nitrogencan form bubblesin the blood and tis- sues much like carbon dioxide bubbles in a soda. Thesebubbles move throughout the bodyand can: 1! lodge in constrictedareas such as jointscausing pain, 2! pinch off and damage nervesand 3! cause paraly- sis. Thiscondition is knownas decompressionsick- ness, the bends or caisson disease. Decompressionsickness is certainlythe most famousdiving illness.It was discoveredin the 19th centuryby laborersworking in tunnels beneathrivers Tokeep waterout of workingareas, the tunnelswere pressurized.Many workers returning to ordinaryatrnos- than blood or other tissues.Consequently, nitrogen is phericpressure at the end of the day developedpain not removedquickly from fat during decompression, in theirloints. Some became paralyzed. The malady making obesitya dangerousproblem. Other factors to considerare the intakeof certaindrugs, metabolic became known as caisson disease, Thedisease remained a mysteryuntil 1907 when stressessuch as sleep loss,hypercoagulability blood J.S.Haldane developed "stage decompression." He that readilycoagulates!, high altitudediving and work found that decompressionsickness could be avoided rate at depth, by bringinganyone who had been in a high-pressure The U.S. Navy has developed tables that tell environmentto normalatmospheric pressure in grad- diversthe maximumnumber of minutesthey can ual stages.This eliminated the formationof smallbub- theoretically stay at certain depths and stil! avoid bles of nitrogenin the blood and tissues. decompressionsickness. But abiding by thoselimits Dependingon wherebubbles lodge in the body, does not guaranteesafety. The U.S.Navy diving the symptomsof decompressionsickness may vary tables are based on evaluations of trained, healthy Figure9!. In mostcases, symptoms begin within an men. Sport diversrange widelyin physicalcondition hour,but they make take longer sixor morehours!. and ability. Otherfactors also increasea diver'schance of devel- The only effective treatment of decompression opingdecompression sickneM;. Age, obesity, extreme sickness is immediate recompression in a hyperbanc fatigue,alcohol, old injuries,extreme hot or coldwater, chamber.Recompression increases the pressure anddehydration can hinderblood circulation and pre- ventnitrogen from quickly entering and leavingthe blood.Fat absorbs about five times more nitrogen

C/51 CHEMISTRY PART 4

around a diver as if he were diving!, reducing the size Chairfes' Law of the bubbles and forcing them back into solution. Then the pressureis slowlyreduced to allowthe diver 1. Examinethe graph. Does the graph show a direct to decompressgradually. At the first signs of the or an inverse relationship?Why? bends, a diver should not hesitate to seek treatment. Time is critical. In North Caroiina,the only recompressioncham. ber is at DukeUniversity in Durham.They havea E facilityfor decompressionsickness treatment. Duke Universityalso sponsorsa DiverAlert Network DAN! that provides information to divers and physicians temperature nationwide 2. On a hot summerday you take your air tank to a Questions diveshop to be filled.You then have to run a couple of errands,so you place the tank in the trunk of your Soyle'sLaw car.The tank wasfilled at 20'C and your car trunk is 31 'C. Hint. For every 33 feet of descent from the surface, the pressureincreases by 1.0atm. Surfacepressure is a! Whatwill happento the temperatureof the gas 1,0 atm. rnolecules in the tank~

1, Holding his breath,a diverleaves the surfacewith b! What will the gas at 31'C do in the tank? 4.0 liters of gas in his lungs.What is his lung volumeat a depth of 66 feet? c! If the tank is filledto its maximumcapacity, what do you think might happento this tank in your trunk? 2. Youare diving to a wreck at 132 feet. Using Boyle's law, determine the changes in pressure, volume and 3. Using the graph below, answer the following density with increasmgdepth questions.

Depth Pressure Volume Density surface! 4,0 liters 1.0 kg/liter 33 ft. 2.0 atm 99 ft, 4.0 atm 132 ft.

3. A diver is at 33 feet .0 atm of pressure!and the 3o 25o gasin his lungsoccupies a volumeof 1.0liter. What volumewould his lungs occupyat the surface?What a! What volume corresponds to a temperature of volume at 99 feet? 25'C? 13"C?

4. You dive to a wreck off of the North Carolina coast. b! lf you werefilling a tank for a diver,which tempera As youreturn to the surface.0 atmpressure!, you ture, 25'C or 13'C, would allow you to add the maxi forgetto breathe a big mistake!Will your lungs burst mum ainount of gas? Why. under the fOIIOwingSituatiOnS? USe BOyle'S law and show all work. Human lungs can only expandto four Oalton's Law liters. 1. The total pressurein an air tank is 8 I0 mm Hg

Pressure Volume of Wngs Site Depth a! If the pressureof oxygenis 150mrn Hg, what is the A 66 ft 3.0 atm 3.0 liters partialpressure of nitrogenin thetank? Assumeoxy B 132 ft 5.0 atm 1.0 liter gen and nitrogenare the only gasesin the tank ! C 99 ff 4.0 atm 0.50 liter D 66 ft 3.0 atm 0.33 liter b! Whatpercentage of the gasin thetank is oxygen? Nitrogen? C f 52 CHEMISTRY/PART 4

c! Is this the compositionyou breathenormally? Test Questians

2. What is the partialpressure of oxygenin com- 1.A diverdescends to a wreckat BOft. He staysthere pressedair from a scubatank breathed at 132ft? in too long and realizesthat he is out of air. He swimsto mm Hg and atm! Use the percentoxygen from the the surface quickly. introduction. a! If the diver holds his breathduring the ascent,how 3. In deep diving, divers breathegas mixturesof willthis affect his lungN Which gas law explains thiN helium and oxygen. The partialpressure of oxygen must be maintainedat 160 rnrn Hg or slightlygreater b! At the surface,the diverfeels pain in his!oints, He to avoid toxicity. In a helium-oxygen mixture breathed suspectsthat he hasthe bendsWhy might he have at 500 feet, what percentageof oxygenwill resultin developedthe bendN Applythe appropriate gas an oxygenpartial pressureof 210 mm Hg? lawsin youranswer.! How might he get rid of the pain? Henry's Law 2. Defineeach gas law. 1. Draw a graph that shows the relationship between pressure and the amount of gas dissolved in a liquid. a! Hoyle's b! Charles' 2. At which of the following depths would a diver have c! Dalton's a higher partialpressure of nitrogenin his blood. 33 ft d! Henry' s or 132 ft. Why? 3. Name the gas lawthat appliesto each of the follow- ing conditionsand explainhow it applies.

a! Lungs burst b! Nitrogennarcosis c! Squeeze d! Decompression sickness

4. Drawgraphically the relationshipthat appliesfor eachof the followinggas laws.

a! Boyle's b! Charles' c! Henry' s

5 What are the partial pressures of nitrogen and oxy- gen in the lungs at 0 ft? Do these change with in- creasing depth during a dive? Explain.

6. Rapid ascent rates may contribute to the cause of decompression sickness. True or false.

7. Helium causes decompression sickness in much the same way that nitrogen does. True or false

8. What is the PN~of air breathed at 99 feet under water? in atm and mm Hg!

C /53 CHEMISTRY/PART4

17.The formation of gasbubbles in thebloodstream is 9,Air pressure is higher, lower!at the top ofa tall called buildingthan itis at ground level. 10.Why arewater pressure changes somuch greater 18.What is the purpose of holdpoints during a diver's thanairpressure changeswith a change indepth? ascentto the surface~ 19.A gasis more,less soluble! ina hotliquid than it 11.For every 10meters 3feet! ofwater depth, divers experienceanadditional atmosphereis in a coldst liquid. of pressure, 12,Name three body areas where divers notice pressurethe most. 13,Hve does scuba gear keep thediver from experi- encingpressure inthe body cavitied. 14.Name three problems thatair in the bloodstream can cause? 15.During a dive, gases entering thelungs are ab- sorbedtoa greater,lesser!extent intothe blood- streamthan when the diver ison land, 16,As the diver ascends, gasesdissolved inthe blood- streamdonot stay dissolved. Theybecome bubbles inthe blood Name three problems thatgas bubbles cancause for the diver?

C/54 CHEMISTRY/PART 4

ACTIVITY 4 Underwater Research Facilities: Hydrofag

Purpose and a shower Divers use a lockout dry tunnel where water meets air of the same pressure to access the lab. To teach about saturation diving in underwater Divers using this facility undergo extensive train- facilities. ing, On the first day, they are delivered to an area above the lab, They dive to the lab, set up and begin Background their work. Within 12 hours, they are saturated and The number of people involved in diving activities have ad!usted to the change in pressure. For the next has increased steadily. This increase is found in scien- week to 14 days, the divers work in shifts to perform tific, recreational and commercia! diving. Because of their experiments. The boat returns daily to bring this heightened interest, there is a need for equipment meals and compressed air tanks and to check on the and proceduresthat would allowa diver to operate divers. with greaterflexibility, safety and effectivenessand for On the last day, the divers close the tunnel and longer periodsof time. Althoughsignificant achieve- start decompression. The process takes about 14 mentsare being made towardsworking at greater hours. When decompression is complete, divers suit depths,particularly by offshoreindustries, much work up and return to the surface. Then they return to the is still confined to waters less than 300 feet deep. land station for at least 24 hours to guard against any Pioneering work in the 1930s indicated that satur- post decompression problems. ationdiving might be feasibleand providedivers the The lab allows scientists to perform experiments that would be too difficult or impossible for divers extended time and depth needed. Under saturation conditions, divers spend 24 to 36 hours under depth- workingfrom the surface.Scientists use the lab to pressure tc become saturated with an inert breathing study marine biology, geology, chemistry, physics, gas probably helium!.Once a diver is saturated,the ocean dumping,resource development and ocean required time for decompression is the same regard- technology, less of how long the diver stays below. Researchers developed underwater research labs Questions where divers become saturated and work for days to 1. What gas lawsapply to the definitionof saturation weeksat greaterthan normalpressures. Hydrolab in diving? the Bahamas is one such facility. At Hydrolab, divers are saturated at 50 feet, allowing dives to greater 2. If a diver doesnot go througha completedecom- depths to occur more easily. pressionsequence what may occur? Why? The length of a dive usuallyproves to be the greatestlimiting factor for scientists.But workingout of 3. What is a surface interval? Hydrolab, divers can work longer at their research sites and are able to obtain new air tanks without hav- 4. What is the ambientpressure at Hydrolab? ing to endure long surfaceintervals between dives. A approximate! surface interval is the time required at the surface be- tween divesto graduallyrid the body of nitrogen.The 5. What two factorsdoes Hydrolabextend for research greaterthe time spent at the surfacebetween dives, divers? up to 12 hours,the longer the next dive can be. Hydrolab is a manned habitat operated at arn- 6. Are diversusing Hydrolab likely to developnitrogen bient or surfacepressure. Located at 50 feet,the lab narcosis? Why? saturates divers at this depth. Three to four divers live in Hydro!ahfor up to 14 days.Hydrolab is an 8-by-16 7.How long does it takea diverto saturateat a new foot cylindncalchamber with a 3-by-10foot submarine depth?How long does it taketo returnto surface dry transfer tunnel, The habitat contains two bunks, pressuresaturation? lights, a communications radio, toilets, windows, tables

C l 55

CHEMISTRY/PART 4

4. The ratio of the volumeof the popped corn to the from the whole class. volumeof the unpopped corn is called expansion volume.The popcorn industryuses expansionvolume Remember.Label the axes of the graph and show the as a test of quality. Orville Redenbacher claims his unitswhere appropriate. Protect the points on your gourmet popping corn has an expansionvolume of graph with circles,squares or triangles.Make the 40 to f. What is the expansionvolume expansion graphcover as much of thepiece of graphpaper as ratio! for the popcorn used in this experiment?Show possible.Draw a best-fitline on yourgraph. Give the mathematically how you arrived at this answer. graph a number and a title,

5. What substanceis presentin a larger amountin the 9. A datatable must accompany the graph. Give the normal kernel as compared with the oven-heated tablea title.The columns in yourdata table must have kernel?In which kernelwas the internalpressure titles and unitswhere appropriate.The columntitles greater before popping? shouldbe: Expansion Volume, Percentage Water P%%d! and Sourceof Data.The Sourceof Data column 6. Which kernelproduces more desirablepopcorn, shouldcontain the first names of thelab partnership the normail or the oven-heated? from whom the data was obtained, NOTE.Do not put units on data in a data table if the 7. Reread the lab introduction and answer the follow- unitsare already specified in thecolumn headings. ing questions.Would popcorn pop fasteron Pike's Peak or in Durham?Why? 10,At whatdepth in the oceanwould the pressurebe equivalentto the pressureinside a popcornkernel just 8. Preparea graphof expansionvolume dependent beforeit pops 9 atmospheres!?Give your answer in variablewith no units!as a functionof thepercentage feetand meters.Ignore significant figures, of water independentvariable with o%%d units!. Use data

C! 57 CHEMISTRY/PART 4

AGTIV'ITY 6 Sea Squeeze

Procedure Placea freshmarshmallow ina belljar and reduce Torelate thechange inthe volume ofa gastoa thepressure inthe lar by using a vacuumpump, The changeinpressure onthe gas Boyle's law!. marshmallowiswhipped and contains air bubbles. As theexternal pressure isreduced, the air bubbles in Background thernarshrnallow willexpand. The rnarshmallovii looks likea monstercorning alive as it grows. Shipsatsea often bag and weight garbage, then Aspressure returns tonormal, the marshmallow dumpOccasionallyit overboard.garbage containing Styrofoam cups shrinks.Ifthe vacuum pump is left on too long, the air ee~ fromthe bags. Thehigh pressures atgreat bubblesinthe marshmallow willburst. When the pres- depthsinthe ocean compress theair in the cups, surereturns to normal,the marshmallow willshrivel. squeezingthemintominiatures. Thisbasic idea ofthe Thenstudents can see an airless marshmallow. changingvoiume ofa gaswith a changeinpressure Aninteresting extension ofthis demonstration isto onthe gas can be illustrated usinga rnarshrnallow combineseveral marshmallows into an artistic crea- anda vacuumpump.In this case, airwill be expand- tion.For instance, you could make a snowman. inginstead olbeing compressed. Aninternational treatycalled MARPOl-Annex V,~ as an Questions actbythe U.S. Congress in1988, bans all dumrxng bycommercial 1,How are pressure and volume related, inversely or vesselsintemtorial watersof the high seas, U.Smilitary vessels are directly? exemptrintrI 1994 2.Write a mathematicalequation that relates pressure Equipment/Nlaterials and volume. vacuum pump 3.Use Boyle's law to relatethe marshmallow exercise bell jar rnarshma'Ilows fresh! to a diver s lungs,

C/58 CHEMISTRY/PART 4

ACTIVITY 7 Diver's Lung

Purpose Procedure To relatethe change in the volumeof a gas to a Puta smallamount of airin a balloon.Tie it off so change in pressureon the gas Boyle'sIaw!. no air escapes.Place the balloonin belljar. Reduce the pressureby usinga vacuumpump. As the Background pressurereduces, the balloonexpands because the Thefirst effect divers feel when descending into pressureinside is greaterthan external pressure. As the ocean is a "squeeze"on their lungs becauseof the pressurereturns to normalthe balloonshrinks. the increasingambient pressure.Breathing corn. Tomake this demonstrationa littlemore in- pressed air will equalize the pressure inside and out- teresting,a messageor drawingcould be puton the side the lungs and relievethe squeeze. outsideof theballoon. The message/drawing should An ascendingdiver experiencesthe opposite be smallso thatit is hardlynoticeable until after the balloon expands. pressure-volumeeffect. Diversnot breathingon ascent feeltheir lungs expand. A diver'slungs can only ex- Questions pand 15to 30 percentof their originalvolume without bursting. Smart divers breathe on ascent so that exter- 1.How are pressure and volume related, inversely or nal and internalpressure is equalizedand the normal direct!y? lung and air space volume is maintained. This pressure-volumerelationship can be illustratedby us- 2. Writea mathematicalequatio~ that relates pressure ing a ballonand a vacuumpump. and volume.

EquiprnenUIHaterials 3. Use Boyle'slaw to explainthe changesin a diver's lungs as he descends or ascends in the ocean. vacuum pump bell Iar balloons

C/59 CHEMISTRY/PART 4

ACT IVI TY 8 PressureVersus Volume Experiment

decimalplaces. Record this measurement in your Purpose datatable in a "Heightof Water"column. Toillustrate therelationship between the pressure Movethe buret down again so that the water level coincideswith the 3,000-rnl mark on the graduated andvoluine of a gas Boyles' law!. cylinder.Read the water volume inthe buret; and recordit in yourdata table. Before moving the buret Equipment/Materials fromthe 3,000-ml mark, use the metric ruler to 4,000-rnlgraduated cylinder measurethe distance between the water level in the 50-ml buret graduatedcylinder and the water level in the buret. smallergraduated cylinders Record this measurement. metric ruler Continuethis process of movingdown 500 ml, measuring,and recording until you can go no further Procedure downin the graduatedcylinder. Fillthe 4,000-ml graduated cylinder to itstop Addthe necessary volume to eachreading to ac- graduationwithtap water. Letthe water situntil ithas countfor the water that is filling the unmarked part of reachedroom temperature. Thecylinder could be filled the buret. thenight betore the lab,! Closethe stopcock onthe buret. Use a small Questions graduatedcylinder toadd approximately 6 to10 ml of 1.How can you determine the total volume of your tapwater to the buret. Putyour finger over the open end of the buret; in- buret? vertthe buret; and lower it into the water in the 4000-mlgraduated cylinder. Remove your finger. 2. Whatis the total volume of your buret? It will not be Raiseorlower the burst until the water level inside 50 ml.!Record as many significant figures as your theburet coincides with the water level in the measuringdevice will give. graduatedcylinder. Atthis point, isthe pressure being exertedonthe air in the buret greater than, less than, 3.Calculate the volume of airin t'he buret at each data orequal toatmospheric pressure? Answer: equal! pointby subtracting thevolume ofwater from the total Whileholding the buret so the water levels inside volumeof the buret.Record the answersto your andoutside theburet coincide, read the volume of calculationsinthe Volumeof Air"column in your waterin the buret. Be sure to read the graduations datatable, Show your calculations. onthe buret to two decimal places. Remember to readthe volume ateye level. Record this volume ina 4. State Boyle's law. data table. Movethe buret down into the graduated cylinder 5.Write the rnathernatical statement of Boyle'slaw that untilthe water level inside the buret coincides with the showstwo different pressures and volumes of the 3,500-mlmark on the cylinder, Read the volume of same gas. waterinside the buret.* Record this volume inyour 6.Assume that the first volume ofair in your data table data table. wasmeasured at roompressure. Use a barometerto Hasthe water 'level inside the burst risen or fallen? Answer: risen! Why did this water level change determinethe atmospheric pressure in theclassroom. occur? Answer: Pressure onthe air in the buret is Recordthis pressure inthe "Pressure onAir" column greaterand the air takes up less volume! in yourdata table. Whileholding the buret's water level at the 3,500-mlmark, use a metncruler to measure the 7.Use Boyle's law to calculate the pressures related to distancebetwee~ the water level in the graduated theother air volumes and record them in yourdata cylinderand the water level in the buret.' Take your table.Show your calculations. Do not forget to use measurementincentimeters, and read the ruler to two units.

C/60 CHEMISTRY/PART 4

8. Basedon the data in your data table, how are the buret becauseof the procedureused in this pressureand volumeof a gasrelated, directly or experiment. inversely 14.Give two sources of errorin this experiment. 9, Using your data, make a propergraph of volume versus pressure. 15,How is thewater we usedin thisexperiment dif- ferent from seawater? 10,Based on the water height and pressuredata, how muchdoes the pressureexerted by the waterchange 16.If a diveris 50 feetdown in freshwater, would he for each centimeterof water height?HINT: Get an experiencemore or less pressurethan if he were50 averageof the DP/2 h calculationsShow your feetdown in oceanwater? Why? calculations. 17 Imaginea diverdescending into the ocean.What 11.In freshwater, pressure changes 1.00atmosphere will happento the volumeof hislungs and the air in- for every 34 feet of water height.Convert this to at- side? Why? mospheres/centimeter.Show your mathematicalwork. 18.What could happen to a diver'slungs as he 12. Using the resultsin questions10 and 11,calculate ascendsif he doesnot exhalewhile ri9ng? your percent error for change of pressurewith depth of water. Show your mathematical work. 19.Today scuba gear is commonly used for diving in the ocean.What words are representedby eachletter 13.What other substance in the gaseousstate! was in the acronymscuba? introducedinto or increasedin theair trappedin the

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