'DOCUMENT RESUME

AUTHOR Griffitt, Joe H. And OthersTITLE ''''l Teacher's Guide for Balloonsi and Gases.INSTITUTION Elementary Science Sthdy, Newton, dass.SPONS AGENCY National =Science Foundation, Washington,ZEPORT NO ISBN-07-017714-7PUB DATE, 71

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MIS PRICE MF01/PCO2 Plus Postage.DESCRIPTORS Elementary' Education; .*Elementary School Science;

Instructional Materials: *Physical Sciences; *Science.Activities; *Science Course Improvement Projects;Science Curriculumf Science Education:, ScienceInstruction; *Teaching Guides

IDENTIFIERS *Elementary Science Study

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50p.; Photographs may not reproduce well,

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ABSTRACTThis guide iras developed -to provide children with an

opportunity to prepare and collect ,several common gases and todiscover and work with some of their properties. The guide is dividedinto five major sections; (1) introduction, (2) materials, (3)

activities, (4) balloons aloft, and (5) an appendix. The introductionprovides information concerning use of the guide, grade level,scheduling, and evaluation., The materials, section lists 2m1terialsneeded for this unit. The activities section describes activitiesinvolving biomothymol blue, carbon dioxide, oxygen, hydrogen, andmystery gases. The Balloons Aloft section describes a concludingactivity: The appendix provides information on safety precautions,preparations, recipes and techniques, and the yardstick balance.

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Elementary Science. Study

Webster Division, McGraw -Hill Book CompanyNew York St. tLciui San Era ciao() Dallas Loni:lop ney Toronto,.

The Salloo ps,attd Gases. Teacil*r's'Guide for Balt/64;1-1s and Giases

Class I

!I

Re*ted VnitsGases and ':'Airs41V1Ysteil-:Owyders,Clay eoal.,%`;Sink,or F1161Senior:BatpriOkig

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Gopy ,Q E..) "1971,'1968 by EducationInc. All Rights Reserved

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'Except fdr the rigttis to/material reServedby'others;, the pu and the copyright ownerhereby grant 0 i,s§ion to domestic persons ofthe United State and Canada for'use of this Awork withoOrdtiarge in the English language inthe United St.ats:andCanada after JanUary 1;

./ 1976, prOVideb th4t publicatibns incorporatingmateriafS covered by these copyrights containthe originl/CO0Yrightfnotice and astaterneni.thA.the pUbilbation:is not endorsedbYthb driginlcopyright_0Wrier: Foiconditions'of use and-0ermission'to:USe materials 4.-

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reface.

The Elementary'Science Study is one, of many ctirriculbM development programsin the fieldspf, science, social studies;andrhathernOcs-unde-r:prep'arationat EduCatiop 'Development Centel',

,

; 'Inc. EDCi(a private nonprofit org.anization,incorpOrating the InstitutelorEducationalInnovatign,and Edubational Services

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, l-ncorf)oted) began in 1958 to develop'new idea and methods for improvingthe content end process of education.

ESS has been Suppqited prirriarily bygrantS,from the Ntrona1 ScienceFoundation:Development of materialsfor teaching science from kindergartenthrough eighth glade started on'..a small ,

scale in 1960. The work of the proj'ecthas since involved more than a hundrededucatois in the conception 'anddesign of its units of 'study. Amongthe staff have been scientists, engineer,s,mathematicians, and teachersexperienced in working/Withstudentsof ,all ages. fromkin.drgarten,througnc011ege. ,

ciuipment, and'printedmaterials are produced withthe help.

'// of staff specialists, as well as of the film',/ /and,photography studios, the design-labprartiory, and the proguctionshops of EDC. At every stage- of ',1development ideas and ar.e

taken into actual classrooms, wherechildren help shape the-forth and,c,o6tentcf each, unit before it is'releasedtoSchools everywhere.

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Acknowledgments

"Thielidea for this unit originated

theWilliam Bertozzi first tried some of

:the activities with children in the Summer9f 1965. The following year he, GeraldWheeler, and Robert Gardner..rnOdified:the equipment and activities for furtherteaching and prepared a draft of ate'acher's guide. This was taugheon a.limiteci basis and 'was revisedby'Gardheradd issued as aTrial Teaching Edition,t .

called Ballobns, in the spring of .

I 1068. The unit has been revisedconsiderably on the basis of trialteaching.

>Sister Lucy Malarkey of the MayfieldSchool in'Pasadena, California,contributed heavily ter the present edition.She taught several different versionsofthe revised Guide and helpedwith developmental work. Her classroomnotes were Wonderfully detailed andhelpful.

The entire ESS staff lent editorial'assittartce for this writing. Edith H. E.Churchill and Emily Rorhney made manyhelpful and astute suggestions.Frank Watson shared with me his'experiences ir)classrodgs and workshops.Adeline Nairrfan provided editorialassistance and much encourageMent.Mary S.Gillmoi contributed:in too.,rranyways to mention: .

The photographs were taken by JoanHamblin, Major Morris; Sister :JacquelineJelly,,/and Sister Alice Callaghan.

Joe H Griffith

Iv

Using This' Guide

Grade Level and ScKedPling

Eyaluation"2:n

Activities

'Work with Brortiothymol Blue (BTB),

More BTB, and Carbon Dioxide

ecting and Testing Carbon Diokide

Exploring Oxygen

Wqrk with Hydrogen

Mystezy,Gas'es

7

8

11

18

20

26

"Ba llodns Aloft"A Finale 29

Appendix

Safety Precautions

Preparations, Recipes, and Techniques,

The Yardstick Balance

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31

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32

38

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Introduction

There are -Many ways to learn things, andonly one of therrinvolves reading a book:Science deals with the behavior of thereal world. Doing experiments, Watchingthings happen, observing animalsallthese activities are "lessons,: richerin content than any textbook.

Gases are often very mysterious tochildren, becduse a gas may be invisibleand yet hays properties that can beobserved. Adults take the existence anddiversity of gases for granted, but formany children he spaces in the world arefilled with "nothing." It is a big jump togo from this nothing to a something'.

Generating and trying to identify :mystery gases on the basis of theirearlier experience carries the studentsa step.further in their investigations..

There is a logic to the sequence ofactivities in the Guide, but therp hasbeen no attempt to provide for allstudents' responses or'to encompas.allthe possible questions thatare interestingand worthwhile to explorrlf you treat'the activities as a series of lessons toteach or as experiences for your stu entsto work through in order and"finish," you and they will miss much ofthe unit's richness. If the equipment ',.;

called air. It is an even bigger jump . is available, the students will come back,to realize that air is made up of several ''''at later times and in iiTtferent ways,kinds of gases and to think of ways to tell to those questions and experiments thatdifferent gases apart. intrigwe them. C.

BALLOONS AND GASES provides children

with an opportunityto prepare andcollect several common gases an:dto discover and wofk with some of theirproperties.

If yOu follow the sequence suggestedin the Guide, the students work first withacids and bases and with the coloredindicator bromothymol blue (BTB). Theseactivities give experience with a'fewsimple chemical reactions andwith some of the'pr&perties-of acidsandbases. Furtriermore, they introducestudents to a method for distinguishingbetween fluids that look alike.

Next, students generate gases thatare "invisible." They try to identify anddifferentiate between these by weight, bythe reactions of the gases to a-solutionof BTB or limewater, by theireffect ona flame, and by other indications.

In this unit, students will/pe able to

control many. different chemicalreactions. The ones by which the gasesare generated and identified suggesta whole range of related questions andexpldratiOns. For example, students maywent to look .more closely at-

1. The behavior of BTE3 as a colorindicator

2. How the proportions of theingredients affect the amount ofgas that is 'produced

3. The way a-Catalyst acts.to produce,_a gas, as.in the case of potassium..iodr6e and hydrogen peroxide

4. Dry Iceas a starting point forinvestigating the same substance indifferent states, and the strikingchange in vyilume which occurswhen a substance changes from asolid to a gas

5. Questions relating to buoyancyand density., which often arise_when students compare a heavy°carbon dioxide balloon and a'floating'hydrogen balloon (Howmuch does the hydrogen weigh?)'

Any one of these or similar topicsmay become the focus of the activitiespf some or all students at particular times.their own ideas and interests are oftenthe best guide to rich learningexperiences.

One further note: Some teachers havefound ithelpful for students to workthrOUgh,BAI;LOONS AND GASES before theyundertake the ESS unit GASES AND-AIRS," which looks at similar questions

-in a more sophisticated way.

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Using This ,Guide

Before you teach BALLOONS AND GASES,read through this Guide andliy outsome of the activities and experiments

.-for yourself. Some teachers feel that-their, preparation to teach these sciencematerials is inadequate and that they

,should use only topics with which 'theye.'re'familiar. If you feel this way, you may

-..be relieved to know that some of thebest learning situations occur when the

- teaoher is "discovering.' alOng with thestudents. You. need to have the materialscarefully prepared and available, butyou don't need to have all the answers.

The Appendix contains importantafety precautions and instructions

for aSsembling.some of the equipment.AI °included are directions for making thethr e gases (oxygen, hydrogen, and.

\

i;(' carbon dioxitle)-vfor doing ceftain tests,andffor collectin6 gases. Some of the itemsin ec,Ap.Pendix repeat items in the text.

e Appendix is meant. to provide a 'yick reference in which you_can findrecipes and instructions gatheredalltogether.

The Guide does not proyide:NOu withmany explanations about the-chemical °reactions and properties exhibited by-thematerials. The omission is intentional.-Thp value of these materials lies in thestudents' using them with pleasure-tofind answers by experimenting andobserving: Refer to a chemistry textbookfor detailed chemical explanations ofyour students' investigations if you feelyou need them.

In trial classes, BALLOONS ANDASEShas been taught successfully in thesequence offered in the Guide. There is,however, nothing sacred about this order,.and you should feel free to alter it if youprefer another sequence or if thestudents'investlgations suggest adifferent order in your class. You may,however,want to follow the Guide thefirst time you teach the unit.

A number of Ouegflons related tothe activities are included in each section.How you use them is up to you. Theyare not necessarily to be "answered."Perhaps the, will help. you further'

/the interests of particular students Or ask.

askstimulating questions of an experi-menter who needs help.

There will betimes when ydu will wantto bring a few students.or the wholeclass together to share their results and-pause to consider what others are doing.You and your-students must judge when

.class drscussioji is useful and whenit would bean interruption.

Here are a few Suggestions about sharingideas that may be helpful:

Full-class discussions are only rarelysuccessful. Usually only a fewarticulate stwftentsdo the talking,While others get lost or "turn off.'. So .

keep large-group discbs4ons orpresentations brief.

Students often don't hear oneanother. At some point, it might beuseful to pair off students and havethem interview each other. Results .

of these interviews could be sharedwith the class orally orin writing.

Often the class will divide into afast group, many of,whom already

.know about gases (these are oftenboys), and,,a slower groUp of studentswho work methodically. It might be ,

useful to .have, separate group dis-c_usgions. Sometimes a measure ofisolation giveS students who Workmore slowly the confidence tocontinue at their own pace, evenif others are far ahead.

?Grade LeveL-and Schedulihg

The activities in the Gpide will takebetween twelve acrd twenty class periodsof about an hour each. The unit cango 15;inger if students become interestedin further investigations.

BALLOONS AND GASES has been taughtsuccessfully in grades five through eight:The initial activities (working with BTB,,vipegar,ammonia, baking soda, andcitric acid)' are fun for people of all ages.

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Evaluation -

How are you going to find out if thisunit has done anything for you'r studentsyou can ask trignn, and you can watch.

What each student (earn from this"unitwill depend in large part. Upon the effort heputs into the work. tudents will differ.On what.things.strik them as interesting.

There are several thing you might lookfor as evidence of lea Ingo Are the'students interested in what they aredoing? Dothey suggest different things

to investigate that you haven't ii/entiOned?Do they do relateddhings at home? DO:they get involved ifi their ownexperirhents?

The last activity of this Unit, Mystery.Gases, can be used as a kind of evaluation.-The. way the students tackle a new prob-Igm ordook at rievi./ experiment willgive you sOme'indic...ation'oi the extentto which they can make use of theirearlier exRgri,gn.cs ',gs with gases. Whetheror not they'identify thg gas is not asjrftportant as their haVing the Confidericeto taoklethe.problem. 2

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ri,, ..,,,,,,,,......._, r

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4.. LL..,...:..an 4.-, ,,.3..1 ' . , ...

t, CLASS. KIT l'(NONEXPENDABLES).

".

This Kit contains laboratory equipment'which can be reused many times. Most ofthe items.are available separately onlythrough chemical supply houses.

15 Erle.nmeyer flasks;32 1-hole rubber stoppers (to fit

the flasks). 16 4-117. stiff plastic tubes 4.1

." 1 0 -2-oz plastic dropper bottles withcaps .

20. 4.-oz plastic dropper bottles' withcaps

250: 1-oz plastic graduated medicinecups

30 onelpiece vinyl droppers4,0 .1-7tsp measuring spoons20 .1,-pt plastic containers with

snap-on lids,..6 3-ft lengths of flexible vinyl tubing

D.)

15 pairs ofsafety glasses30 flexible plastic vials (6" x 1")

2 1-qt,polyethylena narrOw-mouthbottles with screw caps

4 1 -pt polyethylene narrow-mouth"bottles with screw cap

1 liand pump (to blow up balloons)1 set Multi: Purpose Balance parts

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CLASS KIT 2 (EXPENDAbLES)

These pre all expendable items. Tor'epface them locally might require con-siderable effort. In order to teachBALLOONS AND GASES a.,secondlime, youshould need to reorder only this Kit.

2 gross round balloons (ekpandable'to 8-in..diameter)

'300 wooden coffee stirrers300 wooden splints50 pressure=sensitive 1",x 3" labels

5 gr bromothymol blue powder,-sodium salt

1 mossy zinc 5'

5 pt concentrated hydrochloricacid

lb potassium iodide crystals2 lb citric acid crystals,1 oz i-rhagnesium ribbonA lb hydrated lime pOwaer,1 lb limestope chips6 pieces soft glass tubing, 8 in. long

5

MATERIALS TO BE OBTAINED LOCALLY

The following -equipment.is to beobtained-locally. While thispay be aminor,nuisance forsomer-it-does give'yougreater budgetary flexibility and maysave duplicating some common equip-ment. Certain itemssoh as Alka-Seltzertablets and.hydrogen peroXide solutionneed to be purchased fresh; they deteri-orate when stored for a long time. Youmay wantto.buy all these materials,borrow some, or have the childrenbring them in. The total cost of this groupof items should bearound $10...

1 yardstick15 .paint buckets, pails, or containers,

roughly 1-gal size (for water andwaste)

1 gal whitevinegar4 lb baking kda .

1 qt household ammonia ( ;earrecommended)

7 pt hydrogen peroxide, 3% or 6%solution (107volume or 20-volume)

1 pkg wboden,safetymatches(10,smallboxes)

30 small jars (such as baby-food jars)for dispensing baking sodaand citric acid,

Old newspapers1 quart bottfe with cap (suCtr aS a

vinegar bottle)sponges

. 1 jar soap-bubble solution or.liquid detergent

1 roll aluminum foil (25.ft), 1 ball string

2 paper pie plates (for balance.pans)Alka-Seltzer tablets, 2 to 4per student

oyster or claM shells

.10. lb. Dry Icemmer and cloth gloves to

handle Dry Ice

Note: If you,want to explore filling.balloons with helium (see page 29), you.rnay_be able to borrow a cylinder .

from a science laboratory in a universityor industry. Helium also comes insmall containers. One source is ',JerichoIndustries, Charlotte, North Carolina28203.

6

Activities

1111110111--

460.

-4)74' e

Work with BroMothymol Blue (BTB)

MATERIALS. For each. student: .

3 1-oz medicine cups1 eyedropper

For each group of 4. students:1 2-oz plastib squeeze bottle of BTB'1 4-oz plastic squeeze bottle Of

vinegar'1 4-oz Pfasticsqueeze,bottle of, ..dilute,arrimonja:-

t;t4newspapersspongesextra medicine cups ,

You should have the above materialsassembled and the solutions preparedpi'ior to the beginning of class. Beforeyou begin, spread newspaper's out ondesks and have spongesavailable forthe inevitable spills and messes.

When all the groups have a supply ofmaterials, suggest that each student takea little of each liquid in a medicinecup. Urge the students to usethe eyedroppers. Ask them to see whathappens when different liquids areadded to one another, drop by drop.

Sooner or.later, some student will claim.that the BTB has turned from blueto orange or yellow.

".Oh took!" Drop BTB in vinegar andit turns yellow."

"'BTB in vinegar, and it eats it up!"

tan you turn it back to blue again?"Ammonia is stronger than vinegar."

'See Appendix for instructions on preparation.

7

"I like ammonia 'cause it saves youfrom vinegar."

is there a* color "between'," blue andyellow?

"I don't know, buts, I:11 find out.""'I got five shades of green('

You will need to have waste bucketshandy for each group, so that they canempty their cups and start again.

"I'm 'trying to figure out h'ow.,1 can getthe ammonia white again,"

"Ca'n'l take fresh stuff and try it-

agsin?"Wdinder if thet'samrnonia.ym afraid_to smell it because it stingsmy eyes."

How does the ammonia solution feel?Take some on your finger and rubyour thumb and finger tOgether.-Hoyvabout vinebar?

What do the liquids taste like?(Ammonia is. poisonous to drink;To tasteit safely, wet your fingertip withammonia and touch your tongue.)

"Sharp.""StrOng.""Sort of sweet and sour.""Nothing."

After the students have worked withthese materials for about a class period,you might take a few minutes toshare experiences and talk. The questionsHow do you turn BTB yellow? andHow do you turn it back to blue? mightreveal some disagreements amongthe students. If so, let the students

. present their evidence. If theystill disagree, urge them to go backto the materials again.

//hat does spit do to BTB?

8

More BTB, and Carbon Dioxide,

MATERIALSFar eachstudent: -

3 2-oz medicine cups1 eyedropper1 6" x 1" plastic yial

Wooden coffee stirrers

For each group of .4 students:buckets 'for water and for waste

2 i -tsp measuring spoons.2 jars_or baby-food jars

..(jar citric,acid, labeled)(jar baking soda, labeled)

Flavesavallable.the materials from the .preVous activity. You may want to tiethe measuring spoons to the jars. Workon newspapers and keep spongesavailable. Have the gas collectionequipment (next section) in reserve.

;If your room has no sink, you can usethe buckets to bring in water and han-dle,waste water. One-gallon polyethyl-ene pails are cheap to buy and easyfor students to handle. Clean two-

', pound coffee catis Or milk cartons canbe used.. .

You might start off by asking the studentsto put a little citric acid 'powder (about

teaspoon) into one of the medicinecups. Add some water to it, and stir. Whathappens? Where.did the citric-acid go?

"Hey, it disappeared." ,"Citric acid lealies the Water clear".

What does the solution taste like?"Tangy.""Oooh, it's bitter."

What do you think the citric acid solutionwill do to a BTB solution?

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In ohe'class, students added some sugar.to their citric acid and made "lemonade.'"R is all right to drinkthis mixture if yotiadd lots of water to dilute the acidenough so that it doesn't taste too sour.

-Students with sensitive stomachs candevelop a stomachache from too muchacid..1_Jsually a drink 'of water will setthat right, but-a little baking soda is sureto help.

Will the baking soda dissolve as th citricacid did?

"Baking soda turns the water white."-

What effect does a baking soda solutionhave BTB? On citric acid?

Once you have introduced baking soda,it .won't be long until; someone discovershow to make it fizz. This activity willdominate many children's interest for a ',

d

w hile. Others may stick with making the. BTB change colors.

. ,

Wheat do you think Would happen if ,the ;

baking Soda-and-acidmixture startedfizzing? What would happ ,en ifit wasin a cloed space? Many children will bemystified..

"Wow! Look at all that fizz..1 didn'tknow it had such power."

ome of the students will know that agas is' being generated. Can they suggest

`a -way to collect the.'gas?

Someistudents are excited by the'fizzing or by the'very active reactionand try to make bigger fizzes by dumpingtogether everything they.can get theirhands on: You might urge thein totry to collect the gasor to maka,thelayered cylinderdescribed begow. Letthem know you have only a limited supplyof materials.

1Those students who continue workiwith the BTB and the acids and basessometimes come to a dead end and

.can use a suggestion. Here is -one thatmight' be useful:

Use the 6-inch cylindrical.plastic(A narrow drinking glass or olive jar willdol,Put about 1- inch of baking soda inthe bottom of the vial, and pour brri topdf that about an inch of BTB solution.Don ,t mix them NoW add'iinegar asgently as possible, trickling it slowlydown the side till-you've added about3 inches of vinegar. With luck, the mixturewill layer and give a beautiful slow reac2:.tion that is -fasciriat7ng to watch andfun to work with. rir

10

.

Collecting and Testing CarbonDioxide ,

MATERIALS:.rlenmeyer flasks*balloons (about 3 per student)balance with yardstick beam, (SeeAppendix for construction, details.)

paper, clips:2 1-hole ru5ber stopper'S per flask

4-in. stiff plastiC tubes to fit the,

1/4 siopperswooden safetymatChes(smalrboxas)wooden splintshand pump

. _

the Erlenmeyer flasks with the colleOtionapparatus attached tip easily. they are morestable if Placed in4cle.heavy jars, such aspeanut butter jars.

Have on hand all the materials 'usedtill now. To pfepare the,balanceVieadof time, get a yardstick anrave threeholes drilled in it aS,SPediped. in theAppendix: Also, have a look at page 42in the Appendix,' which shows notri

-to weigh fractions of. a paper -clip,using a balance-beam rider. °

Qive those students who want i/ anopportunity to try to Copenct,the gas intheir own way. Occasionally, a student will

up with, an, irigenious' idea. MOStoften, however, studentS' won't, but theirfumbling around and theirlinsuccessfulefforts-pill -tell you agreat .cieal aboutwhat they think a gas is, and how

. -

..-,

t ey think it behaves. (th4 tcp'Rendix hasintUctionsnfo'collecting a gas.Y

Alf,stohents.want some ideas, you can,sugiest thatthey put.a dry mixture of

teapbon each of_baking soda andcitric acidinto aliask, add about2 ounces,,of water, and Allen quickly putaballocin4oVer the top of the'flask.:

- What happens to tt\i balloon?

Don't b surprised if quit a fewstuderig want to do 'this; de they ,peewhat happens,

'

'

What car ,you do with-a balloonful'of gas?

In one .clasS, some boys ran races .

by dropping tWo balloonsat the sametime one filled witecarbdp dioxide .

and one filled-with. room air. saidthe carbon dioxide won because __

it Was -heavier.!'<1. _.

Younight challenge the students to findout ifra carbon dioxide balloon isreally heavier than an air'palloon.AfYou haiie ebalance with/a yaidstick.;bearn.(see diagram,' in Appendix forconstruction detafls), tha balloons can

rbè aocUrate19-weft2c1-:

1-1ovv mud? heavier . .?-. " _

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4

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,

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<4"

Uzr

etAberstopper.

'bal10bYl.

- .

Does it depend on how full theballpoais?

How much does air alone we4h?"I thought the air would weigh more,

but the gas is more.,::

The hand pump can be used to fill aballoon with room air.

In order to perform some of.thechemical tests with carbon dioxide, itf is convenient to have a more permanentcollecting device."Use the stiff plastictubes in the Kit that fit into theCne-hole rubber stoppers."These rubber.stoppers will fit the Erlerrieyer flasks.The accompanying diagram shows how,to connect things.

With this device, its easy to do the BTBand limewa<1.ter tests and to collectenough gas forseveral flame tests.. Be.

.sure to use plastic tubes: Pushing. glass tubes into -tubber stoppers may

break them.yOur balloorikis straight, the

gas goes in easier."

Children often Comment that the flaskfeels colder as the reaction goes on.

When the balloon is full, or the reactionin the flask has stopped, twist the .

balloon and press Your fingertip on thetop end of the tube to prevent thegas escaping:Then remove the entire .

collecting device from the flask.

13

BTB Test

To do the BTB test, pour about 5cc ofBTB solution in the bottom bf aclean. medicine cup or small glass. The

`BTB shoilld be blue or blue-green.Then put the bottom end of the-Collector'tube, Still attached to the balloonof gas, into the BTB, and allow the gasto bubble gently through the BTB..Control the bubbling by pinching theneck of the balloon.

If you have carbon dioxidein the balloon,the BTB will gradually turn from blueto Yellow. You can repeat the test withthe same BTB by using a few dropsof dilute a'rnmonia solution to turn the

._ BTB bliie once agaihDorryt usetoo much ammonia, or it will take a _

great deal of carbon dioxide to turn the------. BTB Yellow again.

d,If you bubble ait'119pugt) BTB,what happens?'

Several things can go wrong with thistest-YoU.can have the BTB too basic,that is,, "too blue." (The BTB shouldturn yellow with the additton ofone or two drops of.vinegar.) Another -thing that can happen isethat you

y get acid.in the collectbr tube, and

'el7

t e acid alone will turn the BTB.low. This usually happens when a

vigorous -reaction *afters liquidup into the tube. Rinsing the tube beforeyou put-it in the BTBwiil take care

'of this. Still another-problem arises whenchildren shake theft tubes and getthe balloon full of the reaction mixture.Helping such children acquire amore refined experimental techniquecan be quite challenging! ,

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ne.wg+te

LimewAter Test

The limeWater test is carried out inthesame way as the BTB test. Place'about 5 cc of limewater in aclear, cleancontainer and bubble the gag throughit. Carbon dioxide. turns limewater milky.

"Look what happens.when I put gasin limewater. It turns whitiqh.Alka-Seltzarish."

"The limewater has all these. littlecrystals in it."

Js tte limewater reaction reversible,.like the BTB test?.

What.does room air or your breath dowith the limewater test? With theBTB test? Is. there much carbon dioxide?

"1 blew into limewater once, andit turned cloudy."

wig

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Flame Test

What effect does carbon dioxide ha eona flame?

A splint will burn in air. Willit burn icarbondioxide?

What can you collect the gas in so yocan test it and see what happens?

In orte class, students suggethedputting a flame near the frrouth of agas-filled balloon and letting some Oscome out or.thrusi'ing a flamingsplint into the balloon. Others objectedthat the moving gas would put outthe flame or that the gas would escapeWhen a splint was put into theballoon operiing.,-

One way to simplify a flame test is tocollect the gas in a jar. Half-Pint plasticjars are provided in the Kit.

How can you filAthe jar with pure carbondioxide that isn't contaminatedwith air?

Here is one method that works. Fill-abucket or a pan about three-quarters fullof water. Put .the jar in the bucket

,.-so that it fills up completely with water,turn itUpside downy and raise itso that most of the jar-sticks out of thewater but Water stays in the jar. .

To get the carbon dipxide gat from theballoon into the jar, put the bottomend of the colfector tub into the waterdirectly under the jar a d, by relaxingthe pressure of.your fi gertip onthe top end of.the tube-allow the carbodioxide to bubble_slowly up.insidethe jar. When,the jar is filled with carbodioxide (that is,.the.Syater has beenforced out of it), cover it, whife it is still

16

yr

21

r.

,f

_

'under,water, with the lid or withanything flat that seals the top. Thenremove the jar from.the water::.

To do the flame test, the students takea burning splint, remove the lidfrom the jar, and..diP thi splint into it.

What happens'appens to the splint?

What happens to the splint whenjar has rOOm air in it?

A girl, in one class argued that the flamewent out because it couldn't get .

arly air in the jar, She repeated theexperiment with an air-filled container.

The flame testProvides a method fortesting whe:le the carbon dioxide 'is..Take the lid ofj,the jar of carbon dioxide.Pretend that the carbon dioxide isa thick:_viscous liquid that pours verySlowly.

Can you pour the'oarbOn dioxide intoanother jar?

You can use the flahle test to see ifyou've succeeded,

The next activities inv ve makingand testing oxygen. You will probablywant to gb on to these activitiesafter the Students have made carbon

fedioxide, have done the BTB andlimewater tests with it, have collecteda jarful of the gas, and have donethellame test.

Exploring 04geny.,

MATERIALS5 pt 39'0.hydrogen'peeoXide solution

(or 3 pt.6°'0 hydr.Ogen peroxidesolution)

lb potasiiurrisiodidegas_production.,and collection,equipmentWOoden splineswooden safety matches(small boxes)

Have on hand all the materials used uptill now.

. What is the air we breathe?

Many students reply that it is oxygen:.In fact,-; airhasbnly a.small percentage of.oxygen in it. Here isa way to ,makepuie oxygen.

Into Ihe flask or bottle you use for gasgeneration, place about teaspoon ofpotassium iodide crystals.Add'.3 our1des,..of 3% hydrogen peroxide solution(or't'' ounces of 6% solution). Place theballoon-rand-tube collector in theflask after a few bubbles have come up.-In five to ten minutes the reactionWill be finished,,and there will be enodghoxygen in the balloon for the tests.(The light brown. color in the flask is fromthe iodine. This will stain clothesand other things. In one class, a studentgot iodinle all ov.er his shirt: ,Hismother got it Out with hydrogen

. peroxide.)

Does oxygen have the'same propertieS, as air?

'18

tY

Ma_.What does oxygen do'if you bubble itthrough BTB or liMewater the way youdid carbon dioxide and. air?

How does the flametest work with a _

jarful of oxygen?

After the students have tested aflaming sprint in oxygen, have them trya glowing sPlint. Get the end of awooden splint burning well; then blow itout. Usually the end will continueto glow red. Insert the'glowing splint intoa freshly collected jar of oxygen.What happens?

Can you repeat this test using thesaine jar of oxygen?

Dcres oxygen "pour" the way carbondioxide does? Which is heavier,carbon dioxide or oxygen? How canyou tell?

Some students might become interestedin the reaction that produces the oxygen.

To get more,Yiirygen, should youuse more hydrogen peroxide or morepotassium iodide?

What effect Mies the amount of 4,

potassibm iodide have on the speed atWhich the Oxygen is produced?

If you warmed or cooled the hydrogenperoicide solution, would this haveany effect on the reactibn?

Children talk about the fact thatthe flask itself feels hotter as the reactionproceeds": Some-racall that it got 'coolerwhen they were making carbon .dioxide.

In one class, a student suggestedthis experiment..

"Can _I do this? I want to put potassiumiodide and hydrogen peroxide'to make oxygen in one balloon andput citric acid and baking sodato make carbon dioxide in another.

-balloon, and then put all thegas together and see what happensin the flame test."

.The ESS unit GASES AND "AIRS"offers additional ideas for work withgases and suggests a method todetermine the amount of oxygenpresentin a gas mixture..

Work with Hydrogen

MATERIALSmossy zincdilute hydrochloric acid (4 molarsee Appendix)

paper clipssafety glasses (for those who donot wear eyeglasses) '

gas production and collectionequipment

balloonsstringbalance (see Appendix for assembly.

.

'instructions).2 paper pie plates

yardstick beam,

You will probably want to reread thesections of the Appendix dealing withsafety. Be sure each student is wear-ing comfortable safety glasseS or hisown eyeglasses.k

Place the balance .with pans wherestudents can reach. it easily to weightheir zinc. See the Appendix for in-structions on assembling the balance.

Prepare the diluted hydrochloric acid-"ahead of time. Have only the dilute. acid .available to the students, and

pAtt the concentrated acid away. Bersure to label the acid bottles, i,ndicat-

ing clearly which is dilute and which isconcentrated.

Put the dilute hydrochloric acid wherestudents can conveniently get to it, .

without crowding.: Since there is

bound to be some spillage, have onhand paper towels, water for washinghands, and baking soda to neutralize.spilled acid.

if there are other,balances aroundyour school, you might hav,e°,.a couple' ofthem availablefor weighing6th `tyre "..

° zinc, and reserve the yardstick balance .

for inVastigating the weight of the.balloons.

20 o.;

2J

The production of hydrogen oftencreates excitement among the students.To begin the class, you may want tohave.a brief review of safety precautionsand of classroom procedures. Tellthe student's that they are going to beable to make.hydrogen, using zincand hYdrochloric acid (also calledmuriatic acid). Point out that the acid youare using in the class has been diluted(twO parts water to one part acid)

. and that wearing some kind-of glasseswill prOtect the eyes from spattering.However, stress that the studentsmust be careful.

In making the hydrogen, the studentsshould first weigh out the zinc andplace it in the empty flask. Thenthey should measure out andpour in thedilute hydrochloric-acid. Tell themto wait a few seconds after the reactionbegins before putting on the gascollector, so that the hydrogen can drivethe room air out of the flask.

Use about 8 grams of zinc (equalto about 12 #1 paper clips in weight)and 2 ounces (60 Cc)'of the diluted .

hydrochloric acid.

Mossy zinc varies widely, so thatthe reaction.Aime may vary from fiveminutes to half an hour. Cautionthe students not to shake the flask, sincethis will cause acid to bubble upinto the balloon. A swirling action willsuffice to "mix" the materials.

When the bubbling has ceased and thereaction has alMost stopped, theballoon can be removed and tied off.A piece of string tied to a balloonwill help the student hold onto it.

21

Can yogi determinhow much acidremains in. the solution in the flask whenthe reaction has finished?

If you add BTB to the solution, whatcolor does it appear?

How many drops of ammonia does itnow taketo turn the solution bltle?

The acid.remaining in.the flask can beflushed down the drain. Any solid;inc remaining in the flask can be rinsedOff. with water and returned to thezinc supply:

The floating hydrogen lolloOns willprobably produce lively confusion in theclassroom. Students need time toplay with them and slotof experiencesto help theMmake,sense of whatthey see.

How much string wth the balloon lift?

Several worthwhile games have beeninvented by students. Three boyshad balloOn races to:see whose balloonwould get to the ceiling first. Severalgirls tried to get their balloons.tohang in the air, neither rising nor fallihg.

Can:you-use hanging balloons to chartthe air circulation in the room?

How many paper clips will a balloon' lift?

How much does the hydrogen inside theballoon weigh? (That is, what isthe weight of the balloon plus.hydrogenplus string, minus the weight ofthe balloon and string?) The yardstick

,balarice is sensitive enough forworking on these questions.

After, a period of working with thehydrogen,,a brief disCussibn and sharingof thoughts might be useful.

22

You might use one of t e abovequestions to get a dis ussion_started..Give the students a chance to share theirthinking about the experiments andto explore their differences. The question.How much does the hydrogen. insidethe balloonweigh? is a particularly gibodone to explore.. When differencesarise among the students, encourage

..,them to suggest experiments.that mightresotve the disputes and if possible,therf.give them a'chance.to.go babk

. to the materials. ..

Flame Test

The hydrogen flame test is spectacular.

Fill a halt-pint plastic jar with hydrogenby bubbling it through water. Closethe jar with the lid, and remove it fromthe water. Light a wooden splintand bring the flaming splint to the jarjust as you remove the lid..Poof!

The"por from a half-pint of hydrogenis safe enough in the classroom.A large amount of hydrogen (severalquarts) When mixed with air canproduce enough of an.explosionto ring 'your ears. Plastic containers aresupplied in the Kit bebause plasticis preferable tolfglass for this experiment.Do not use large (pint or more) glasscontainers to hold hydrogen.

For another experiment, turn thejar of hydrogen right side up and leaveit open for a few seconds beforeinserting the burning splint. Whathappens? Will the same thing happenwith carbon dioxide? 4

What effect does hydrogen have on BTBor limewater?

- 23

Hydrogen Soap Bubbles

MATERIALS.,6 8-in. pieces of soft glass tubing

6 3-ft pieces of flexible vinyl tubingmossy zinchydrochloric acid, diluteErlenmeyer flasks'one-hole rubber stoppers4-in. stiff plastic tubes to. fit therubber stoppers

commercial soap-bUbble solution orliquid detgrgent

Before the claSs begins, you will needto make a flange on one end di eachpiece of the soft glass tubing. To dothis heat the end of a tube in the tipof a flame from a Bunsen burner,Kopane. torch, or gas. stove. 'Rotatethe tube so that it heats evenly. Whenthe glass i,s soft, spray the end of thetube by applying pressure inside thetube with a piece of Metal, such as alarge nail.

,Without the flan e on the end, it. isoften difficult to et the bubble offthe end of the tube witl-mUt breakingit.

The students should continue to wearfheir safety glasses.

Connect the tubing as shown in theaccompanying diagram.

Soap bubbles provide a dramalicand pleasing demonstration of some ofthe properties of hydrogen..Thehydrogen gas is generated in the flaskand passes through the flexibletubing. The flanged tube_is dipped intoa soap. solution, and the gas expandsthe soap film on the end into a bubble. If

2432.

--11111

r

you shake the bubble or blow on it,it will leave the tube and rise-in the room.

The bObble can be Ignited with alighted splint or match.

This is terrific!""We need more soap because our

bubbles are too thin."""I made five bubbles together.""Gee, this is the greatest thing

I've ever done."."Every time the bubble blows up,

it puts out the match.',"It-exploded, and I felt soap splash. ,all over me.""There't a bubble stuck on the

Why do thefirst few bubbles fall?

What happens with carbon dioxidebubbles?

Mystery Gases

'MATERIALSgas production and collection.equipment

cups.BTBlimewaterwooden splintsbalance with yardstick armdilute hydrochloric acid (4 molar)vinegar'limestone or marble-chip&magheeium ribbonaluminum foilAlka-Seltzer tablets (2 to 4 perstudent)

Haveon band all the materials usedup till now,

Now that the students have made carbondio de, oxygen, and hydrogen, andh e an idea of hoW thecse gases behave,y u can challenge them with someu known gases. All the g/tses producedb these reactions are one or another"

the three gases they have alre. explored, but you needn't tell the

-

students that. h. a

It is up to you to decide the bestway for your class to work at mysterygas activities. You might have thewhble class tackle one mystery gas at atime, or you mighthaVe severaldifferent mystery gas reactions goingat once. For convenience, you willprobably want to have thee whole classwork with Dry Ice together.

26

MAGNESIUM RIBBONCut-off about 2 feet of the magnesiumribbon:Put about 1 ounce of dilutehydrochlorj;$ acid in the flask,and add fie magnesium ribbon.

What the gas produced?

Will magnesium ribbon react withvinegar? What is produced?

LIMESTONE OR MARBLE CHIPSPlace enough of the limestone or.marble chips in a flask almost to coverthe bottom. Add 2 ounces of dilutehydr:ochloric acid.

What gas is produced?

To produce a larger quantity of gas,would you add more chipS ormore acid?

What happens if you use vinegarinstead of the acid? °

ALUMINUM FOILCut a strip of aluminum foil about6 inches square, fold it up intoa small, flat package and 'place it inthe flask. Pour:about 2 ounces'of dilute hydrbchloric acid into thefltsk.What gas is produced?

(This reaction often takes a while.to get started,'but once begun, it goesquite vigorously.) ^

ALKA-SELTZER TABLETS ,

Place some water'in a flask, andthen drop in an Alka-Seltzer tablet.

What is the gas produced?

Do two tablets give twice as muchgas as one?

What effect do the tablets have on thewater temperature? Does the tabletbehave the same in ice -cold water?In warm water?

9.

.SEASHELLSIf yob have a supply of oyster or

'clam shells available, put in' the flask- about 20 grams1(1 ounce by weight.

of shells, and add 1 ounce (liquidmeasure) of diltite hydrochloric acid. .

What gas is produced?

DRY. ICEYou wi need the following materials:Dry lc slabs (Obtain from hospitals,cot/ ges, or ice-cream vendors;10 ounds is plenty.)

clot glovesham ergas collection materialspaper cups

purchase the Dry Ice as close to classtime as possible. It can be kept for aday.Or so if wrapped in newspaper andstored in a Slyrofoam picnic cooler or,better- yet, in a freezer. Keep it inthe newspaper wrapper, even in thefreezer.

With gloves or some other protectionfor your .hands, plade one oT the DryIce slabs in 'a bag and, break it intosmall pieces with a.hammer'..

Since Dry Ice is tAcinatirib to eXperimentwith, give the students a small supplyand time to explore its possibilities.Provide them with paper cups. and water,and tell them, to drop small pie esof Dry Ice in the water. The bu bling andvapors that follow are exciti to

see and talk about.'

The.gas collectors should, be available,. so that students can try to collectand identify the gas evolved when,,theyare ready.

427

ps

4

"Balloons Aloft"A finale

t.41

In one school, several classes ended theunit by sending up balloons withPostcards attached. The postcards,

- addressed to the school, containecithe.requestthat the finder writedownwhen.and where he found them.One class ran out of zinc andhydrochloric acid to make hyrdO*6en for,the balloons. They borrowed acylinder' of helium from a nearby sciencelaboratory.

Here is what their teacher wrote:

The kids were in high ger, andreally excited over the prospect of"balloons aloft." In the end, wemanaged. to get five postcards (cut irfhalf and some cut even smaller)airborne. Whether or:,not any will everget through the mail and backagain remains to be seen. They'llprobably get lost in_ the mountains,

C,

gafetiPtecautions

Safetiplasse

In this. unit, the.students',andthe-teacher shduki wear .afet'glass,es oreyeglasaas When handling::hydrochforrclatid or when rnakingandieetIng.,:l.'..;.hydrogen. The chief danger te or. 2spattering acid into the eyes.

:There are 15 pairs of safety galssesin the Kit. Students who wear glaese,can continue to wear their. ownglasses: Schools often have a;subbiyof safety glasses.

It isImport ant that the safety glassesbe comfortable and that they fit

;snugly on the students' heads..lf theycomfOrtable, they won't be

worn continuous y: If they don't fit'+enugly andfall off easily, they become, ahazard. In Onclass, the only acid spillse,'

,resulted feom'shidente' safetylasses falling off their faces andocking over the flasks.

Glass Tubing arid; Jars1 .

The tubing to,be,used with theOne-holes rubber i'vere is plastic.Vyhite it is p '131 'a use glass

'not ady sable. A very 1

4 comb labOratOry accident occurswhen^7 you try to put glass tubing :into arubber stopper. The glass tubing is

.easily snapped off and pushed through7,-your hand. A

There are plastic jars supplied inthe Kit. It is wisaio use these to db the,flame testsparticularly hydrogen.A large amount of hydrogen mixed withair can.giye enough of an explosion

ti

"zt

to shatter a glass jar, so do-not collecthydrogen in a large-glasS container .

(1-pint or larger)'. ,

Acid

The acid supplied inihe Kifis .

concentrated. Whenyou: haictle_it;.weafsafety glasses. Have -only the, qi luteacid available to the Class. Keep the!.Concentrated acid put away. Label

e bottles clearly.

When.you dilute the acid, pour acid. . -

into water, not the reverse.

, The general rule for acid spills orsplashes is plenty of water. Spills arenothing topanic about. The diluteacid used in.this unit will not everraffecl*your skin if washed off immediately.Baking soda can be'used to neutralizeany acid spilled on the floor or furniture.Sprinkle baking soda on the aciduntil it stops bubbling, and then cleanup the mess,-;

If you pour acid down.the drain, follow itwith plenty of water.

If there is no sinktirkyour morn,'hav9' a bucket of Clean water :On bandf="emergencies.

Labeling

One of the most common labratoryaccidents is caused by getteig thewrong bottle. This can be avoided byhaving all bottles arid jars clearlylabeled. Labels are provided in the Kit.They should be put oh the jars and.bdttles before class tirpp.

,

PreParatiOns; Recipes; and Techniques,

The following is a collection ofdescriptionSOPpreparations, recipes, and techniques.1-f-i8y'ar'e gathered together here forconvenient reference: Many of them repeat

. -. information already provided earlier.

Preparing the Liquids: .

1. Bromothymol Blue Scilutiori (BTB)

Supplied in theKifis.a powder whichis the watersbliible, sodiurn salt ofbromothyrnolplpe (sometimes spelledbromthycriOWFor present Ouryoses; yOuwill need a 0.04% solution of BTIEli,.-YoU' 'can inaft& this soluiion in the pint; harrow-

. -cribUtly:Plastic bottle. Put about 0.2:gram(Attie powder (a little less then. the sizeof; pea) in the botile.. Fill the bottlewith 'clean water, cap it, and shakeit to disedly,e the powder.

.

BTB *solution: ige'n indicator of the acidityof' a s011ition;:,arid it charges color in thepH range 6,0 tO 7.61:ft re':01161,, in theacid range,(low pH) .and brue7,in.,tbebase range(highpH): ltthe.!s'Olutionyou make is not blue, it:,ia,tiecause thewater is slightly acidic: ..To. turn. the BTBsolution blue, add .dilute hOdSehold

. -ammonia (see below) to it, one dropat a time, until the solution is blue. 'Don'trrtake it too basid. Two'drops of vinegarshould turn it green or yellow.

2: Ammonia Solutions

The household ammonia which is sold. in grocery stores is too strong to work"withcomfortably..Dilute.it for classrOOm useby mixing four parts water and 'one parthousehold ammonia. Stir or shake well:

You can also Puy-household ammoniawith detergent added to it. Ayoid it if youcan, because the detergent wilt make

lot of bubbles. If it Is notposlikleto get plain ammonia, yob can use the,detergent solution. :.

'BOttfes of household ammonia arelabeled "poiSon.',;:lt is poison wheft;:n-d'.If it is swallowed. It.lrdt.!,1d.not,of ColIrse,be swallowed. knin'opia fumes irritatethethroat. When the ammonia is diluted,the fumes are no longer such a problem:

.3. Limewater Solution

,

Limewater is a cleat solution of hydratedlime in water. Hydtated lime is calciurnhydroxide powder. It is only slightly;soluble in water. To .make lirnewater,,put about teaspoon of hydrated limein aluart bottle (such as an empty clean-vinegar bottle), fill it with distilled waterortap water, and cap the bottle tightly.Shake the bOttle for.a minute or so, andthen leave it undisqurbedat least overnight.A white powdery precipitate will c011edton the bottom of the bottle. This isundissolved lime dhci inscilublecarbonates.

You want only the clear solution.Carefully' pour this oft' into a cleanpint bottle (suppliedin the Kit), disturbingthe settled matter as little as pogsible;Stop pouring before any of the solidscome over. You Can keep a supply oflimewater in the quart bottle and refill'the pint bottle whenever it becomes empty.Thelimewater must be kept tightly,stoppered, so that it won't react with the.carbon dioxide in-the air. .

L.

4. Dilute Hydrochloric Acid

The hydrochloric acid,(12molar) suppliedin the Kit, or available from chemicalsupply houses, is too concentrated to use.safely in the class. To make it 4 molar, .

you must dilute it by adding one partacid to two parts water and mixing therhthoroUghly. Tap water will do. Alwaysadd acid to water: Never add water toacid. There is a great deal.oi heat ofmixing to be dissipated:

d' The concentrated:acidis much morecorrosive than

I

the dilute, and it gives offbiting, acrid fumes. Be sure to wear safetyglasses when y ou. handle ft Label thebottle clearly.

Hydrochloric acid is also called .-muriatic acid.

5. Hydrogen Peroxide.

'Hydrogenpercixicle. can be obtained ... .

frorniudsi&es and discount stores. Ifyott;6Uy"it!rOm chemical supply house, .

,,:.;get the 3:,,,',:; sdlu9on or the 6%.solution.7(sOrnetimes.called.-1 0-volume and

'".ii. -';,... .'.20.'-vollitffe. respectively). Do not get,the stronger 3004 ablution, which Canreactviolentlywith potassium iodide.Hydrogen peroxide deteriOrates if it is .'

not stored propey. It shoUld. be kept inairtight containers, in a cool place, andeither in adark place or inian opaquebottle. In the method outlined. below, 3%

;, 1

hydrogen peroxide will generate a. i

ballOonful of 'oiygen in three to fiveminutes.. lf,,youts takes longer thanthat, you may have e stale bottle. Che0 .

that ydur supply is 'fresh before Class time.: I-

Recipes-kOr Making the Gases

1. Carbon Dioxide"

Baking soda and citric acid ,

Place teaSPoori Of, baking 'soda andteaspoon of citrib; acid-ig,The bottom of

a dry. flask. Add about 2 ounces of water.The as evolved is carbon 'dioxide: Thisreaction proceeds quite:rapidly andwill foam over when larger amounts areused.

2. Oxygen,

Hydr,Ogen peroxide (3% solution) andpotqsSium iodide crystals .

piacei!, teaspoon of pOtassiuM iodide.crystals in, the bottorh of a clean flask. y

Pour in about 3 ounces (9Q MIY6f 3%hydrogen peroxide solution or 1 ouncesof 6% solution. It will, take afew secondsfor the reaction tddet started. The bubblesthat evolve are oxygen. The reaction andthe materials are safe to`tiandle, butsome iodineiiproduced4hat may stainclothes or unvarnishe&wbbVwork 'ifspilled.

3. Hydrogen

Mossy zinc and dilUte hydrochloric acid,.

Weigh out about 8 grams (12 or 13 #1paperclips) of the mossy zinc. onto afolded piece of paper and pour it into anempty flask. Now add 2 ounces (60 cc)of the dili.4e hydroChloric acid (4 molar).Have the40 collector ready. (See thefolldwin6.3`-thereaction will begin almostImmediately. The 'bubbles thatTome offare the hydrogen. These quantities willproduce a little overaquart of the gas.

,33

.Techniques

1. Flaw taCallect the Gas Generated. in a Flask

(a) The sii-pplestway-..iS just tostretch a balloon over the mouth ofthe flask. Allow a little time for theair.

$ in the flask to be forced out by thegap being generated before you--putthe balloon '4. (A plastic bag anda.rubber band can also. be used to.catch the.gas.) When the balloon isfull,.you can tie it off.

.

--,;(1:5)-*A more elaborate, but useful, devicecan be put togettferwith two one-holerubber stoppers and.a rigid tube. Plasticis preferable because of breakage. At ?.-least opeotthe rubber stoppers mustfit the flask in which the gas isgenerated. Put a. ru.b.berstopper at.eachend of the tube: Put one end inthe flask; and stretch the balloonover. the otherend. When the balloon.is -full,twist.the neck, and hold yourfingertip on the top end of the tube

....:-to,.prevent the gab from. escaping.

......Thrs.'device 'is useful because it makesit easier to bubble'the gas through.lirnewater or BTB, and it is easit

:' collect the gas in a jar by bubbling' itthrough. water:.

(c) If you use flexible tubing with aone -hole stopper in the generatingflaSk, jau can collect the gas directlyin a jarover water.

6

34

a.

Col le9,,t some gas in a balloon. Transferthe gas, to a half-Pirit plastic container ."

t2y letting the gas puSh the water out ofthe container.

When the container is filled with gas,slide a lid over the mouth of the containerand remove it frbm the water.

35.

2. How to Run the BTB and LimewaterTests

The BTB and limewater tests areperformed by bubbling. the gas througha small amount of ,the solution. Use a1-ounce medicine cup (Make sure it isclean.) Place about 5 cc of BTB orlimewater in the cup.

. Collect' the gas in a balloon-and-tube'device (as described above), pinch theballoon shut so that none of the gas willescape, and remove the stopper from the.flask. Rinse the bottoin of the stopper andthe tube with fresh water to remove anyof the solution which' may have spatteredon it. This is necessary, because acid onthe tube will change the BTB to yellow, nomatter what kind of gas you have' in it.

Place the end of the tube just under thesiirface of the E3TB or limewater solution,and allow the gas to bubble slowlythrough it.In the case.of carbon dioxide,the BTB should turn from blue to blue-green to yellow .quite quickly. the.limeWater wilt turn milky.

Holcl the neck of the balloon so that nogas can escape.

Let about half the gas slowly bUbblethrough about 5 cc of BTB. What hap-pens? Let the other half bubble through.about 5 cc of limewater. What happens?

3! How to Do a Fleme Test.

With all the gases.made in the unit,it is useful and interesting forthe students to see hoW a flarrie or aglowing ,piece of wood is affected.Once you havea jai' of the gas, you cantest it by uncovering it and dippingin a burning splint.

You can also test with a glowing splint.The.splint will be extinguished in carbondioXide but.Will burst into flamein oxy0eri.(A splint is simply a thin pieceof woodWilidh will continue to glowafter the flame is blown out. Matchstickswill riot usually do this becausethey are specially treated. Coffee stirrers. ...and f)pp§idle sticks will usually work.)

. With hydrOgen, you need to exercise .some Caution. Hydrogen-alone will notsuOport cdrnbustion, but pure hydrogenwill bUrn where it contacts air, and .amixture of hydrogen-with air or oxygenwill explode. A small quantity; such ashalf-pint, will only pop, but have the

.' children wear safety glasses.

To do the flame test, insert a burningsplint into a collected jar of hydrogen..The hydrogen will burn at the mouth of thecontainer where it is in contact with air.The tip of the splint in the hydrogenwill not be burning, but it may reignite ,when it is withdraNn through the burninggas. If air is mixed in with the hydrogen;the gas will pop when ignited. If you areusing a small jar, there is such a small.quantity of gas that this is not dan-gerous. Some students recognize thegas as hydrogen when ey see it burnor hear it pOp.

To do the flame to t. removeothe lid fromthe container, and lower a burning pieceof wood into the gas.

45 37

The Yardstick Balance

For a simple balance to be accurateenough to weigh the gas in a ballcion, youneed an extra-long beam. An inexpensiveyardstick from a variety store will workfine. A piece of lath from the lumberyardWill do. It should be .36" long, 1"wide, andl," thick. (ASk for 1i" lattice.)

The pans made from paper pie platesare lighter than the plastic ones suppliedand increase thesensitivity of thebalance.

Assembling the Balance

tt re koles , 331 in diame Er

Screw tirie upright into the base.

38

Center the yardstick beam in the slot,and insert the pin through the holes in theupright and the hole in the center of thebeam.

4

id

Insert a paper clip through the hole ateach end of the beam.

The paper clip shaild swing freely in thehole. If it does not, bend a larger loop init so that it does.

Making Pans for the Balance

To make pans for the balance, taketwo pape'r pie plates and some string.

a. Punch three holes (equally-:spaced)near the edge of each plate. Use a one-hole paper punch or a sharp instrument.

. d. Insert a finger through the two loopsof sting and slide the string.until the panhangs level.

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b. Cut twy 4' pieces of string.c. Thread a 4' piece Lif string through theholes in a pie plate and tie the endS.

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e. Pinch off'a loop of string near tke.lop.

t Tie this loop into a knot, so that the pancan:be hung from the beam.

g. Repeat the above steps for the secondpan.'Hang the pans from paper clips. Ifthe beam is not level, add a piece of clayto the higher side of the beam.

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A Balance Ridee.

You can use ,a paper clip at different -

positeons on the beam to weigh thingsthat weigh less than one paper clip. Sucha device is called a rider.

1. UnfOld a paper -clip.:-Place it on thebeam so that you can slide it along thebeam. Where can you place this paper

. clip on the balance beam so that it bal-ances paper clip in the left-hand pan?(Cut an unfolded paper clip:in half.)

2. Can you place the paper *clip on thebeam so. that it will balance 1 paper clip?How about !,paper clip? .

_ .

3. Can you now predict where to placethe paper clip to balance two pieceswhich together weigh ; paper clift7Threepieces which .weigh .7, paper clip?

4. Is your 'balance sensitive. enough tomeasure paper clip? How can you:find..out?

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