Microscale Gas Chemistry

AbstractThis article starts with a historical overview of thechemistry of gases from the first mention of air byEmpedocles down through Lavoisier’s Oxygen The-ory. Gas generating equipment is reviewed along theway. The traditional macroscale apparatuses ofthe 19th and 20th centuries are reviewed. We nextdiscuss the tenets of microscale chemistry and howthese apply to gas chemistry. Before introducing theAlyea-Mattson method for generating gases in60 mL syringes, a variety of microscale gas methodshave been developed and these are reviewed. De-tailed instructions for generating gases in large syr-inges are given. We finish with an overview of theeleven gases that can be generated by this methodand list the experiments and classroom that can beperformed with each. Our free website, dedicated tomicroscale gas chemistry is described.

A Brief History of the Study of GasesThe story of the early days of gas chemistry is inter-esting and important. It spans the entire 18th centuryand serves as an example of how an erroneoustheory can shape and misguide understanding andinvestigation. It is a story in which the chemicalbehavior of the gases eventually allowed the geniusof one man, Antoine Lavoisier, to first postulate theprecepts of modern chemistry as we know them evento this day. But before we can fully appreciate thesignificance of the 18th century and the developmentof modern chemistry through the study of gases, weneed to look back to the earliest ideas about gases.

The philospher Empedocles of Acagras in Sicily(492-432 BCE) provided the world with the four-ele-ment description of substances: all matter was com-posed of some combination of earth, air, fire, andwater. This first attempt to develop a comprehensivephilosophy that explained all aspects of the materialworld was broadened a century later by Aristotleso that earth represented the solid state, air repre-sented the gaseous state and water represented theliquid state. In addition, every substance consisted of

primary matter, impressed with form, which was thehidden cause of the properties of the substance. Thefour forms were hot, dry, moist and cold. Unfortunatelyfor science, Aristotle rejected a much more accurateconcept of the material world proposed by two ear-lier Greek philosophers, Leucippus (5th centuryBCE) and Democritos (455- 370 BCE) who believedthat substances were built from small, indivisibleparticles called atoms. Aristotle’s stature amongscholars was so great that for nearly twenty centuriesafter his death he was still widely regarded as theultimate authority on matters of philosophy, fromwhich science eventually emerged.

The Renaissance brought great advances inchemistry and the development of experimentalmethods and scientific thought. Some of these ad-vances involved gases. In the 17th century RobertBoyle conducted his now famous experiments onphysical properties of gases and combustion. He wasoutspokenly critical of Aristotle’s four-element the-ory and proposed his own. Although Boyle’s theoriesregarding the nature of substances were vague andnot very accurate (for example, he believed that firewas a particle), he was one of the most prominentexperimentalists to attack Aristotle’s theory of theelements. Around 1670, Boyle collected hydrogen,which he called factitious air and knew it to be highlyflammable. It is significant and noteworthy that hewas the first scientist to collect a gas in a vessel andto give it a name.

The ability to study gases advanced significantlywith the invention of an apparatus to collect gas bywater displacement by Stephen Hales in about 1700.Hales’s ‘‘pneumatic trough’’, shown in Figure 1, con-sisted of a vessel constructed from a bent gun barrel withone end sealed off and a large glass vessel filledwith water and suspended inverted in a tub of water.

Hales placed substances in the iron vessel andheated them to drive off airs. He was interested instudying the amounts of gas given off from varioussubstances and missed the opportunity to study theproperties of the airs he produced. He did performsome chemical reactions with the device and includ-ing the reaction of acids on iron filings to produce agas (hydrogen) that he learned was flammable. Hebelieved that all the gases were principally ordinaryair and that some had more particles of inflammability.

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Microscale Gas ChemistryBruce Mattson

Department of Chemistry, Creighton University.Omaha, Nebraska, 68104 USA.

114 Educación Química 16[4]

The early 18th century brought with it the phlo-giston theory, which rapidly grew to become the mostimportant new theory since Aristotle’s in that itdominated and framed much of scientific thought forchemists throughout the century. Johann Becher in-itially proposed in his 1669 text that matter consistedof air, water and three earths. His ideas were popu-larized by Georg Stahl in 1703 who coined the wordphlogiston to describe a subtle material possessed bysubstances and could only could be detected whenit left a substance. For example, when wood wasburned, the phlogiston could be noted in the form offire, heat and light. By 1720, most of the significantEuropean chemists embraced the phlogiston theoryand explained their experimental observations interms consistent with the theory.

By the mid-1700s the age of pneumatic chemists inEngland and elsewhere was well underway. JosephBlack, an 18th century physician and lecturer inchemistry at the Universities of Glasgow and Edin-burgh was among the earliest. He definitively estab-lished that gases can have chemical identities and arenot simply airs. His work, published in a 1756 book,focused on alkaline substances and the gas theycontained which he called fixed air (carbon dioxide).Henry Cavendish, a contemporary of Joseph Blackis credited for the discovery of inflammable air (hy-drogen) in 1766. Cavendish was an extremelywealthy and eccentric recluse as well as a masterfulexperimentalist. Like most scientists, Cavendish wasa phlogistonist and at one point believed that inflam-mable air and phlogiston were the same.

It was Joseph Priestley who emerged as the mostprolific and famous of the pneumatic chemists of the18th century. He began his studies on airs at age 38when he moved to Leeds and lived next to a breweryfrom which he had access to a nearly unlimitedsupply of fixed air. It was here that he discovered sodawater, which eventually led to the invention of car-bonated beverages. Using some of the equipmentshown in this famous drawing from about 1770 (Fig-ure 2), Priestley performed hundreds of experimentson gases and is credited with the discovery of eightdifferent gases, a standing world-record. Priestleyknew that the gases he produced were unique sub-stances with their own physical and chemical proper-ties. Despite these substantial laboratory accomplish-ments, Priestley understood his gases in the oldphlogistonic vocabulary of his day and the actualchemical identities of these gases remained completemysteries until the very end of the century.

Pristley’s most famous discovery was that ofdephlogisticated air (oxygen) on 1 August, 1774. Twomonths after his discovery, Priestley visited AntoineLavoisier in Paris and described his experimentalobservations on dephlogisticated air. Lavoisier wasmore intrigued than perplexed by Priestley’s resultsand was soon repeating this work as well as newexperiments with the curious new air. Lavoisier hadalready questioned the value of the phlogiston the-ory and these new results only reinforced his suspi-cions.

Between 1781-1783, Priestley and Cavendishperformed a series of experiments that led to thediscovery that water was composed of inflammableair (H2) and dephlogisticated air (O2). Cavendish accu-

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Figure 2. Priestley’s apparatus for pneumatic experiments. The tubwas for washing linen. The inverted in the foreground is a beermug and contains a mouse [Priestley, 1775].

Figure 1. Collecting a gas by water displacement; originally fromS. Hales, Vegetable Staticks; from The Historical Background of Che-mistry, Henry M. Leicester, Dover Publications, used with permis-sion. [Leicester, 1971]

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rately determined that the ratio of gases was 2.02:1.After repeating the water experiments (1783), La-voisier asserted that water was a compound of inflam-mable air and oxygen. In the same year Lavoisierpresented his new Oxygen Theory and simultaneouslyattacked the phlogiston theory in a paper titled Re-flections on Phlogiston. His famous book Elements ofChemistry (1789) explained chemistry in termsof chemical elements and compounds (along withnomenclature) and within a decade, most Europeanchemists had converted their beliefs to the oxygentheory. History will remember Priestley as an ex-traordinary experimentalist and Lavoisier as a theo-rist and the father of modern chemistry. Priestley’s ex-periments played a significant role in underminingand eventually debunking phlogiston theory eventhough he never abandoned his faith in it.

In retrospect, phlogiston theory was not as faroff the mark as it seems at first blush. Most observa-tions explained with phlogiston can be modernizedby replacing phlogiston with oxygen on the oppositeside of the equation. That is, phlogiston was ‘‘-oxy-gen.’’ Consider the two familiar examples that wereinconsistent in that the first one suggested that phlo-giston had mass while the second one suggested thatit had negative mass:

charcoal → phlogiston

tin (+Heat) → calx of tin + phlogiston

In modern vernacular, these reactions become:

C + O2 → CO2

Sn + O2 → SnO2

No discussion of oxygen would be completewithout giving proper credit due the Swedish chemist

Carl Scheele. Scheele independently discovered oxy-gen which he called fire air in 1773, one year beforePriestley. His work was not published until 1777,however, and by then history had already creditedPriestley with the discovery. A drawing of Scheele’sretort and gas bag is shown in Figure 3.

Understanding the physical and chemical prop-erties of gases played a crucial role in the earlyhistory of chemistry. The phlogiston theory, whichcaptured the minds of scientists for nearly a century,was created largely due to a misunderstanding ofgases. The relationship between gases and phlogis-ton varied throughout the century as the need toexplain certain observations changed. In the end, itwas the experimental results based on gases thatbrought down the phlogiston theory.

The study of pneumatic chemistry in the labora-tory has developed considerably over the last threecenturies. We shall conclude our historical overviewwith a review of some of the equipment used downthrough the years. Hales’s and Priestley’s pneu-matic troughs look odd, but the basic idea is stillwidely use today although it has been modified andsimplified considerably. The modern pneumatictrough has changed little in the past 200 years. Figure4 is from a 1845 textbook, but could easily have beenfrom a modern text or laboratory manual.

A variety of methods of gas generation evolvedthroughout the 19th century. The Wolff’s flask was acommon device employed to generate gases (Figure5.) The Kipp generator (Figure 6), was produced ina variety of sizes and is still produced and widelyused in some parts of the world today. Its most usefulfeature is that it stores gas for immediate use andregenerates gas as it is used, thus providing chemistswith an ever-ready source of gases such as H2S. The

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Figure 3. Sheele’s retort and airbag [Partington, 1937].Figure 4. Use of a pneumatic trough used to collect oxygen, froman 1845 textbook of chemistry [Fownes, 1845].


top reservoir of the Kipp generator contains anaqueous reagent, in this case dilute sulfuric acidwhich is transported to the bottommost chamber.The acid in this chamber rises and comes in contactwith the solid reagent (zinc in the figure) and therethe two react to produce hydrogen. When the stop-cock is closed, the gas pressure pushes the aciddownward until the acid and metal are no longer incontact, thus stopping the reaction. As hydrogen isreleased, the pressure drops and the acid rises in themiddle chamber and more hydrogen is generated.

Perhaps the most familiar of the old macroscalegas generation methods is the pneumatic flask asshown in Figure 7. In this case the gas being collectedis heavier than air (for example, chlorine), howeverother gases could be prepared with this device in

conjunction with apneumatic trough.

In 1992 HubertAlyea proposed aningenious methodfor the safe genera-tion of gases, inclu-ding noxious gases,for classroom use.The method utilizesdisposable plasticsyringes (Figure 8).Unlike any methodbefore, this ap-proach places thetwo reagents in thesame sealed vesseland allows them toreact to produce ga-ses in a self-contai-ned vessel.

The generation and study of gases has been animportant endeavor in the history of modern che-mistry. It has also been an endeavor that has captu-red the imagination of scientists for centuries. FromAristotle to Alyea the properties of the gases havebeen gradually unveiled. The mysterious nature ofgases ---- their invisibility, their oft lack of color andodor ---- have made them subjects of fascination forgenerations of chemists. Equipment to study gaseshas ranged from simple to complex. In the eigh-teenth century the experiments were done by the

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Figure 5. The Wolff’s flask was used to prepare a number ofgases, including hydrogen [Remsen, 1886].

Figure 6. A Kipp generator for generating H2, H2S and many othergases [Brownlee, 1931].

Figure 7. Preparation of Cl2 and HCl in the 1929 textIntermediate Inorganic Chemistry [Bailey, 1929].

Figure 8. Hubert Alyea first described the generation of gases insyringes in 1992 [Alyea, 1992]. Used with permission from theJournal of Chemical Education, copyright 1992, Division of ChemicalEducation, Inc.

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pneumatic chemists. By the late ni-neteenth century, chemistry text-books described methods for studentuse although these were often elabo-rate, and time-consuming. Withinthe past thirty years, laboratory met-hods have greatly improved, espe-cially with the advent of microscalechemistry.

Other Microscale Methods forthe Study of GasesA variety of microscale gas chemis-try methods are currently in use. Ourmethod, which we will describelater, is based on Alyea’s 60-mL syr-inge method (Figure 8, right) inwhich a solid and an aqueous chemi-cal solution are mixed inside a syr-inge. The reaction takes place in anenclosed syringe, virtually eliminat-ing the possibility of exposure of thegas to the experimenter.

Viktor Obendrauf (Austria) hasdeveloped numerous methods of gas

generation using 10-20 mL syringes, small test tubes,soft latex stoppers or septa and blunt needles similarto that proposed by Alyea (Figure 8, left). His refine-ments include the use of a reagent syringe (Figure 9).Much of his work with microscale gas chemistry(methods and numerous interesting experiments)has appeared in German-language journals such asChemie & Schule (Salzburg) but a good overview ofhis methods can be found in his web-based article in

Chemical EducationJournal [Obendrauf,2002]. Among manyingenious features,Obendrauf uses asyringe packed withcharcoal to absorbunwanted gases asthey continue to gen-erate in the reactiontest tube. Oben-drauf’s methods us-ing medical appara-tuses (septa, needles,etc.) for the genera-tion of gases have ledto various compa-

nies marketing the necessary equipment for Euro-pean markets [Menzel, web].

Alan Slater and Geoff Rayner-Canham generategases in one cell of a 24-well plate and collect the gasin pipet bulbs (Figure 10) [Slater, 1994].

An ingeniously small-scale, inexpensive appara-tus is described by Lise Kvittingen and RichardVerley (Norway) in which the reaction vessel is acentrifuge tube and the dropping funnel is a thin-stem pipet. The gas collection vessel is a wide-stempipet and used the method of water displacement(Figure 11) [Kvittingen, 2004].

Certain gases are readily produced by electro-chemical methods and microscale methods for gen-erating gases this way using pipet bulbs have alsoappeared. Per-Odd Eggen and Lise Kvittingen havedescribed the electrolysis of water using one or twopipet bulbs as shown in Figure 12 [Eggen, 2004].

Ozone is also conveniently produced by anelectrochemical method as described by JorgeIbáñez and Bruce Mattson and shown in Figure 13.This method is well-suited for use of gases in situ[Ibáñez, 2005a].

Figure 9. Viktor Obendrauf uses asmall test tube containing a solidreagent with the second reagent ina small syringe; the large syringe isthe gas receiving syringe [Oben-drauf, 2002].

Figure 10. Slater and Rayner-Canham describe the ge-neration of gases in a 24-well plate.

Figure 11. Kvittingen and Verley’s apparatus is similar in principleto the traditional 19th Century equipment ---- only 100 times smaller.

Figure 12. Electrochemical method for the generation of gasesusing a pipet bulb and a 9-volt battery.


Generation of chlorine dioxide for in situ use hasalso been described by Ibáñez, Anderson andMattson. The device which uses a Beral pipet as thegeneration chamber is shown in Figure 14. Thismethod could be extended for use with a widevariety of gases. In this and the previous example,the stem of a Barel pipet has been stretched to 30 cmor more in length so that the gas can be convenientlydelivered to the desired destination [Ibáñez, 2005b].

Microscale gas chemistry need not involve ex-pensive or expensive apparatus. Martin Choi descri-bes making chlorine in a drop of solution in a Petridish and allowing gas diffusion to carry the chlorineto various reagents present in other drops in the dish(Figure 15) [Choi, 2002].

Using a test tube and Beral pipet with slits cut

into the bulb, James Kilroy and Mary Virginia Ornadescribe the simple device pictured in Figure 16 invarious attitudes. An especially nice feature is thatone can stop gas generation at any time by lifting thereaction chamber out of the aqueous reagent [Kilroy,1994].

The Kipp generator, described above and pictu-red in Figure 6 has inspired similar small-scale devi-ces. A 20-mL gas capacity one-piece clear plasticKipp generator, pictured in Figure 17 was inventedin the former Federal Republic of Germany andpopularized by Andreas Kometz and others [Ko-metz, 2001].

From its inception, microscale methods havedeveloped along two lines in terms of equipmentsophistication and expense. Glass manufacturershave created ingeniously small apparatuses that tend

Figure 13. Electrochemical generation of ozone in a pipet bulb.

Figure 14. Use of a pipet bulb to generate gas in situ ---- especiallyuseful for gas samples that cannot be stored because they areunstable.

Figure 15. Gas chemistry by diffusion. [Choi, 2002] Used withpermission from the Journal of Chemical Education, copyright2002, Division of Chemical Education, Inc.

Figure 16. From left: A. Beral pipet with slits cut into the bulb;B. Opening the slits to add solid reagent; C. Pipet in contact withaqueous reagent and concomitant production of gas; D. Pipetraised out of aqueous solution to stop gas generation

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to be expensive, while other methods tend to beinexpensive and use ‘‘consumable’’ plasticware. Fig-ure 18, pictures an example of the former, a micro-Kipp generator about the size of a 250 mL beakerand described by Jinhua Wang [Wang, 2003]. Theaqueous reagent is placed in the left reservoir andthe solid reagent goes in the right reservoir where itrests on a sintered glass frit that separates it from theaqueous reagent.

What is Microscale Chemistry?Among the pioneers in developing and promotingthe movement towards microscale chemistry areMono Singh, Zvi Szafran, and Ronald Pike, foundersof the National Microscale Chemistry Center(NMCC). The tenets of microscale chemistry accord-ing to the NMCC’s website [Singh, web] are: ‘‘to

maintain a pollution-free environment, eliminatingchemical waste at the source without compromisingthe quality and standard of chemical applications ineducation.’’ The benefits of microscale chemistry,according to the NMCC website, are:

---- It reduces chemical use promoting waste re-duction at the source.It offers vastly improved laboratory safety by: • Better laboratory air quality. • Least exposure to toxic chemicals. • No fire and explosion hazards. • No spills and accidents.

---- It sharply reduces laboratory cost.---- It requires shorter experiment time.---- It implements excellent laboratory manipula-

tive techniques.---- It lowers glass breakage cost.---- It saves storage space.---- It improves laboratory skills.---- It provides clean and productive environ-

ment.---- It promotes the principle of 3Rs: Reduce,

Recover and Recycle.---- It creates the sense of ‘Green Chemistry’.---- It changes the psychology of people using

chemicals.---- It is user friendly to people with physical

disabilities.

What is Microscale Gas Chemistry? We agree with all of the tenets given by the NMCCand agree with the benefits cited. We note that theCenter does not stipulate that reactions need to beperformed on the smallest humanly possible scale.Nor does the NMCC define the prefix ‘‘micro’’ orstipulate specific mole or mass quantities. We be-lieve that the spirit of microscale chemistry is toconduct experiments on a reasonably small scalewhile taking into account environmental impact andlaboratory costs. We believe that one needs to con-sider the entire ‘‘account’’ when evaluating the envi-ronmental impact and chemical cost/use for eachsituation. With our techniques, described below,one typically uses 2 mmol of two reagents to generate2 mmol (60 mL) of gas. This gas sample can be usedfor up to five separate experiments. For comparisonpurposes, a typical well-plate reaction, such as aprecipitation, calls for 1 drop of two solutions thatare typically 0.1-1.0 M, or 0.005-0.05 mmol and atypical microscale titration using a 2 mL Mohr pipet

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Figure 17. A 20 mL Kipp generator standing next to a traditional2.5 L model from the 19th century.

Figure 18. Another design of a microscale gas chemistry gener-ator.


as a buret uses 0.2 mmol of each 0.1 M reagent. Atfirst glance, one notes that our method calls for atleast 10 times more chemicals. However, that is justa first glance! Two drops of solution that form aprecipitate such as lead chromate result in a muchlarger environmental impact and laboratory costthan the generation of any of the teaching laboratorygases (CO2, H2 and O2) we describe. The metalprecipitate requires proper storage and eventual dis-posal by a commercial waste handler. Even cleaningthe well-plate requires consumables such as cottonswabs and possibly disposable gloves. If the wellplate is being discarded, that is an expense andenvironmental impact that must be considered.Compared that to the generation of 60 mL carbondioxide via vinegar and baking soda in a 60-mLsyringe, the two-drop lead chromate precipitationreaction has a much larger cost to the institution andto the environment!

The chemicals needed to generate simple gasesin 60-mL syringes cost almost nothing, the resultingsolution can be disposed of down the drain and theequipment can be reused over and over. All (100%)of the reagents used in producing and conducting(20+) experiments with the three gases recom-mended for use in the high school laboratory can bepH neutralized and disposed of down the drain.Over 95% of the reagents that our methods use in all140+ experiments covering 17 gases can be disposedof down the drain. The 14 ‘‘other gases’’ and experi-ments lend themselves well to (a) laboratory activi-ties by second year high school chemistry studentsor university students and (b) classroom demonstra-tions. An unintended use of our gas methods hasbeen in research and development in private re-search organizations, industry and university.

Why Do Microscale Gas Chemistry? Here are the reasons why we are ‘‘gas enthusiasts.’’Microscale gas chemistry:• is fun and easy! Students find it easy to learn how

to prepare gases and do the reactions. Gas sam-ples are ready in 5 minutes.

• is a source of great labs and great demos! Studentsenjoy making gases and performing experimentswith them. They also enjoy seeing classroomdemonstrations with gases. Some of the demon-strations are nothing short of spectacular.

• is visual! The best way to see a gas is to watch itbeing produced. The best way to see a gas undergoa chemical reaction is to watch it being consumed.

The use of large plastic syringes allows for thisvisualization.

• is microscale! It’s microscale in terms of quantitiesand costs, but large enough to see (60 mL). Ourtechniques are in 100% compliance with each ofthe ‘‘benefits’’ described by the NMCC (listedearlier). As an added benefit, the equipment thatwe use is inexpensive and virtually unbreakable.

• is inexpensive. In addition to inexpensive equip-ment, the experiments themselves are inexpen-sive. It costs less than 1/2 cent to prepare a syringefilled with carbon dioxide. Other gases are a bitmore expensive, but never more than a few centsper syringe full of gas.

• is green chemistry. There is little or no chemical waste.• is a valuable resource for teaching a wide variety

of chemistry concepts. Important concepts of thehigh school and college chemistry curriculum canbe taught with gases. Our emphasis mostly on thechemical reactions of gases, however, the list ofconcepts covered includes gas laws, environ-mental issues (acid rain, air pollution), reactionstoichiometry (limiting reagents, law of combin-ing volume, theoretical yield), intermolecularforces, catalysis, combustion, molar mass as wellas more advanced topics such as kinetics andequilibrium. Experiments involving microexplo-sions and rocketry are favorites among the stu-dents.

The Alyea-Mattson Method forPreparing Gas SamplesThe Alyea-Mattson ‘‘in-syringe’’ method is used toprepare eleven different gases. Originally describedby Alyea [Alyea, 1992], the method features thegeneration of gases by reacting two chemicals, typi-cally one solid and one aqueous liquid, inside aplastic syringe. Getting the two reagents into thesyringe before they started reacting was a definiteshortcoming of the original Alyea’s method. In hisarticle, he suggested, ‘‘Into the cap put enough re-agent to generate 50 mL of gas. Drop the cap intothe syringe, and immediately fully insert theplunger.’’ He also described generation of hydrogensulfide as an example! Our contribution to themethod was to develop a safe and easy way to bringthe two reagents together inside the syringe, butseparated so they cannot react until the plunger is inplace, the syringe is sealed (closed system) and theexperimenter is ready. We have spent the past dec-ade working out 140+ experiments with 17 gases.

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Microscale Gas Chemistry KitsEach pair of students will need certain equipment inorder to prepare gases and perform experimentswith the gases. We recommend organizing thisequipment in stackable plastic food storage contain-ers. Each kit should contain the following equipmentas shown in Figure 19. Ordering information, includ-ing part numbers, is available at our website. Severalvendors sell outside of the USA. The most expensiveitem in this list is the syringe. When bought in bulk(4 boxes of 30), one can obtain these for about US$1.10 each. Veterinarians use this size syringe andperhaps one could obtain used syringes from them.Silicone jelly from a pharmacy can be substituted forsilicone oil. Other oils including mineral oil, vegeta-ble oil, petroleum-based lubrication oil cannot beused as they are absorbed into the syringe’s rubberdiaphragm and thus ruining it.

• two 60 mL plastic syringes with a LuerLOK fitting• two Latex LuerLOK syringe caps• two plastic vial caps• one 15 cm length of Latex tubing• one 3 cm length of Latex tubing• one small bottle of silicone oil• one plastic pipet• one clear plastic beverage cup (250 mL/9 oz)• two small plastic weighing dishes• one small test tube (12 x 100 mm)• one medium test tube (18 x 150 mm)• one birthday candle• In addition, each pair of students will need a

wide-mouth beverage bottle for draining and sup-porting their syringes (not shown in figure).

The In-Syringe Method for Preparing GasSamplesThe general strategy of the method is to react twosubstances in a 60 mL syringe. The limiting reagentis always used in solid form and is placed in a smallvial cap. The second reagent is prepared as an aque-ous solution. For example, one could generateCO2(g) from excess aqueous acetic acid and solidNaHCO3, as the limiting reagent.

A. Getting started. Start by lubricating theseal. Lubricate the black rubber seal of the plungerwith silicone oil.

B. The solid reagent. The solid reagent is

placed in the vial cap that is then lowered into thesyringe barrel by water flotation. In the preparationof carbon dioxide, one would use 0.21 g baking soda,NaHCO3. The following quantities of solid reagentsare required for CO2, H2 and O2:

Fill the syringe barrel with water. Fill thebarrel with water. Place your finger over the hole toform a seal. Fill completely to the top.

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ure 19. The equipment that constitutes our microscale gas chemistry kit.

To make: Use:

Carbon dioxide

0.21 g sodium bicarbonate(baking soda), NaHCO3(s)

Hydrogen 0.05 g magnesium, Mg(s) turnings

Oxygen 0.10 g potassium iodide, KI(s)


Float the vial cap. Float the vial cap containingthe solid reagent on the water surface. This is easiestif the syringe barrel is filled completely to the topwith water.

Lower the cap by flotation. Release the sealmade by finger to lower the cap into the syringebarrel without spilling its contents. Allow the syringeto drain into a wide mouth beverage container.When successfully completed, the cap should restupright on the bottom of a syringe with all reagentstill in the cap. The syringe should always be held ina vertical position during these first steps.

Install the plunger. Install the plunger whilemaintaining the syringe in a vertical position. The plun-ger should fit snugly against the rim of the vial cap.

The aqueous reagent. The liquid reagent isdrawn into the syringe as described below. In thepreparation of carbon dioxide, one would use 5 mLvinegar, HC2H3O2. The following quantities ofaqueous reagents are required for CO2, H2 and O2:

Draw aqueous reagent into syringe. Theaqueous reagent, measured into a small weighingboat, is drawn into the syringe while maintaining thevertical position of the syringe. The vial cap withthe solid reagent should float on the solution.

Install syringe cap. Push the syringe cap overthe syringe fitting. It simply pushes on!

Generating the Gas. Shake the syringe in or-der to mix the reagents. As the liquid reagent splas-hes into the vial cap, gas generation will commenceand the syringe plunger should move outward. It issometimes necessary to gently help the plungermove up the barrel.

Remove cap to stop the reaction. After theplunger has reached the desired mark (usually 50mL), tip the syringe so that it is positioned with

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To make: Use:

Carbon dioxide 5 mL acetic acid (vinegar),HC2H3O2(aq)

Hydrogen 5 mL 2 M HCl(aq)

Oxygen 5 mL 6% H2O2(aq)

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plunger downward and syringe cap upward. Care-fully remove the syringe cap assuming that the syrin-ge may be under positive pressure.

Discharge reagents. Turn the syringe 180o anddischarge the liquid reagent into the plastic cup.Caution: Never remove the syringe cap with the capend of the syringe directed downward ---- reagentswill spray out of the syringe. Immediately cap thesyringe with the cap to prevent loss of gas by effusion.

Cleaning the gas sample. The syringe filledwith gas also contains droplets of excess reagents,and aqueous reaction products (sodium acetate in thecase of CO2, for example). There are two options:(1) Transfer the gas to a clean, dry syringe as descri-bed below; and (2) Wash away the drops of aqueoussolutions. To do this, remove the syringe cap, draw5 mL water into the syringe and recap. Shake thesyringe to splash the water around, remove the capand discharge the rinse water. For gases that aresoluble in water, the first method must be used.

Other useful gas syringe techniquesThere are a four other techniques that come inhandy when working with gases in syringes.A. Syringe-to-syringe transfer procedureThis procedure is used when two gases are to be

mixed or when a gas sample cannot be washed(because the gas is water-soluble). In these instances,transfer the gas sample to a clean, dry syringe by ashort connecting tube between the two syringes.The clean, dry syringe is positioned on top. Usuallypushing in on the lower plunger will cause the upperplunger to move outward. Sometimes assistance isneeded.

B. Controlled discharge of gas from a syringe.Plungers do not always move smoothly in theirsyringe barrels. As a result, gases may be dischargedin large unintended portions (such as 40 mL all atonce) if the method shown in the left diagram belowis used. Instead, grasp the syringe by its plunger (rightfigure) and pull the barrel towards your hand. Thissimple technique will give you excellent control ofgas delivery.

C. Discharging a specific volume of gasPosition thumb as a ‘‘stop’’ to discharge desired vo-lume of gas and then push inward.

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INCORRECT WAY CORRECT WAY


D. Preventing unwanted dischargesof noxious gasSome of the gases that can be generated by thein-syringe method are noxious and must not bedischarged into breathable air. These gases are: nitricoxide, NO, nitrogen dioxide, NO2, ammonia, NH3.sulfur dioxide, SO2, and hydrogen sulfide, H2S. Theuse of syringes to generate such gas samples worksexceptionally well and far better than any othermethod in preventing undesired discharges. Thereare two simple considerations to keep in mind when-ever handling noxious gases: (1) Whenever openingthe syringe (by removing the syringe cap), do so withthe plunger slightly withdrawn (by 5 mL) so thecontents are under a slight reduced pressure. Useyour thumb to maintain the plunger in this positionas shown in the drawing. This will allow a smallamount of air to enter the syringe but no noxious gaswill escape.

(2) After the gas sample has been generated,discharge the used reagents into a large cup of waterto dilute them and prevent further reaction.

Clean-up and StorageAt the end of the experiments, clean the syringeparts, caps and tubing with soap and water. Useplenty of soap to remove oil from the rubber seal.This extends the life of the plunger. It may be neces-

sary to use a 3 cm diameter brush to clean the insideof the barrel. Rinse all parts with distilled water. Becareful with the small parts because they can easilybe lost down the drain. Store plunger out of barrelunless both are completely dry.

Experiments with GasesBoth our book [Mattson, 2003] and parallel website(described below) are organized with the teacher andstudent in mind. Part 1 is suited for use by a widevariety of audiences ---- ranging from middle schoolphysical science students up through university-levelchemistry students. Like most experiments and dem-onstrations, results and observations can be dis-cussed and interpreted on a level appropriate for thestudents’ background. Part 1 includes the prepara-tion of carbon dioxide, hydrogen and oxygen alongwith over twenty experiments and demonstra-tions with these gases. Both book and website in-cludes background information for each gas. Thebook includes questions for the students after eachexperiment. In most cases, there are two levels ofquestions depending on the students’ level. (Answersare provided in the appendix.) The website includeshundreds of color photographs, a growing numberof QuickTime movies and numerous links. The webversion also includes electronic versions of a growingnumber of experiments that can be downloaded foruse (with permission). The summary of Part 1 is:

Part 1. Getting Started ---- 3 Simple GasesGetting Started ---- Generating Carbon Dioxidein a Large Syringe. (This section has beenreproduced in this article.)

A. Experiments with Carbon Dioxide 1. Traditional limewater test for carbon dioxide 2. Acidity of carbon dioxide 3. Carbon dioxide extinguishes fires 4. Carbon dioxide and aqueous sodium

hydroxide react 5. Carbon dioxide/carbonic acid equili-

brium

B. Preparation of Hydrogen and Experiments Preparation of hydrogenExperiments with Hydrogen

1. Traditional test for hydrogen 2. Hydrogen forms explosive mixtures with air 3. Reversible conversion of copper metal and

copper(II) oxide

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4. Reduction of iron(III) oxide with hydrogen

Demonstrations and Advanced Experimentswith Hydrogen

5. Effusion of hydrogen is faster than air 6. Hydrogen burns with a gentle flame 7. Disappearing/reappearing candle flame 8. Calcium and calcium hydride produce

hydrogen in reactions with water 9. Deuterium isotope effect

C. Preparation of Oxygen and ExperimentsPreparation of oxygenExperiments with Oxygen

1. Traditional test for oxygen 2. Oxygen supports combustion 3. Dynamite soap 4. Hydrogen-oxygen rockets

Demonstrations and Advanced Experimentswith Oxygen

5. Steel wool burns in oxygen 6. The Blue Bottle experiment 7. Oxygen makes the flame hotter 8. Mini-sponge shooter 9. Chemiluminescence

D. Gas BagsGases can be generated in much larger quantitiesusing simple, gas bags made from food storage bagsand this is useful when students need a supply ofseveral gases. For example, in some experimentsstudents need both hydrogen and oxygen for severalof the experiments. The teacher may use the gas bagtechnique in order to prepare one or both of thesegases for the students in the interest of saving time.One fascinating classroom demonstration is donewith a gas bag of hydrogen: Combustion of hydrogenin oxygen demonstration. A flask as a musical instru-ment?

Part 2. Laboratory ExperimentsPart 2 consists of six full lab period experiments thatcan be used with carbon dioxide, hydrogen andoxygen. These experiments are suited for use by highschool chemistry students as well as university-levelchemistry students.

The experiments are given in approximateorder of difficulty. ‘‘Mystery Gas’’ is a good exampleof an inquiry-based learning lab. Students design anduse a strategy to determine the identities of three gas

samples. ‘‘Percent Composition’’ relates the volumeof carbon dioxide produced from the acid decompo-sition of calcium carbonate to the composition of anantacid tablet. The ‘‘Carbonated Beverages’’ lab is aset of experiments that explores some of the proper-ties of carbonated beverages and relates these obser-vations to those made my Joseph Priestley in the1770s. The ‘‘Molar Mass’’ lab works well for any gas,not just the three we have studied so far. It worksespecially well for heavy gases such as carbon diox-ide, propane. Results are generally within a fewpercent of the actual value ---- much improved fromthe popular ‘‘molar mass of butane lab’’ that appearsin many books.

The last two experiments, ‘‘Limiting Reagent’’and ‘‘Barometric Pressure’’, along with ‘‘PercentComposition’’ all require the entire class to sha-re their data that everyone will then use to completethe experiment.

Part 3. More gasesThe gases described in Part 3 and the experimentsthat go with them should be conducted by individu-als familiar and experienced with gas productionusing the syringe method. Five of the six gases de-scribed in this part have properties that make theirproper use and handling more important than wasthe case for carbon dioxide, hydrogen and oxygen.As with part 1, each experiment comes with ques-tions for the students.

A. Preparation of Nitrogen Oxides andExperimentsList of Experiments:

1. Conversion of nitric oxide to nitrogen dio-xide

2. From nitrogen dioxide to nitric acid 3. LeChatelier principle and the NO2/N2O4

equilibrium 4. High temperature favors the endothermic

substance 5. Acid rain microchemistry 6. Acidic nature of nitrogen oxides 7. Well-plate reactions involving nitric oxide 8. Dinitrogen trioxide is a blue liquid

B. Preparation of Ammonia and ExperimentsList of Experiments:

1. Ammonia is a base 2. Ammonia fountain

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3. Acid-base reactions with fruit juices 4. Ammonia is more soluble at low tempera-

ture 5. Gaseous ammonia reacts with gaseous

hydrogen chloride 6. Ammonia forms nitric oxide in the Os-

twald process 7. Ammonia forms complex ions with transi-

tion metals

C. Preparation of Ethyne and ExperimentsList of Experiments:

1. Ethyne reacts with permanganate 2. Sooty combustible of ethyne 3. Banging bubbles! 4. Ethyne/oxygen rockets 5. Ethyne reacts with aqueous bromine

D. Preparation of Sulfur Dioxide and ExperimentsList of Experiments:

1. Sulfur dioxide reacts with water 2. Sulfur dioxide reacts quickly with sodium

hydroxide 3. Sulfur dioxide and potassium permanga-

nate react 4. Sulfur dioxide discolors many natural colors 5. Acid-rain microchemistry 6. Sulfur dioxide reacts with aqueous bromine

E. Preparation of Chlorine and ExperimentsList of Experiments:

1. Chlorine and sodium hydroxide formbleach

2. Chlorine disproportionates in water toform acidic species

3. Chlorine discolors the natural colors offruit juices

4. Testing colorfast fabrics 5. Chlorine reacts with aqueous sodium sulfite 6. Halogen activity series 7. Chlorine and sodium form sodium chloride 8. Hydrogen/chlorine rockets 9. Chemiluminescence and singlet oxygen. 10. Spectacular underwater fireworks! 11. Liquid and solid chlorine

F. Preparation of Nitrogen and Experiments

Part 4. Catalyst Tube ReactionsIn Part 4 we describe a series of experiments that canbe performed with an inexpensive, commercially

available glass-encased heterogeneous palladiumcatalyst tube. The catalyst tube is suitable for dem-onstrating gas phase reactions in the classroom orteaching laboratory. In all cases, the products canbe tested by simple chemical methods. The reactionsinclude: 1. Oxidation of methane with air 2. Oxidation of ethene with air 3. Oxidation of carbon monoxide with air 4. Hydrogenation of ethene 5. Catalytic oxidation of ammonia 6. Methane and nitrogen dioxide 7. Carbon monoxide and nitrogen dioxide 8. Decomposition of nitrous oxide 9. Nitrous oxide and ammonia 10. Nitrous oxide and carbon monoxide 11. Nitrous oxide and methane

Part 5. Other MethodsIn Part 5 we present five gases that cannot be gener-ated by the In-Syringe Method because the reagentsmust be heated. Instead, we utilize a method that wasfirst proposed by LeBlanc over two centuries ago andinvolves heating two reagents together and collect-ing the gas produced. We have modified the methodto utilize 60 mL syringes for gas collection. TheThermal Method is used to generate hydrogen chlo-ride, carbon monoxide, ethene, methane and nitrousoxide. For each gas, 6-11 experiments are described.Interested readers are referred to our website formore information.

In Part 5 we also introduce a third method forgas generation ---- using a microwave oven. We havefound this method works for generating ammonia,oxygen, carbon monoxide, sulfur dioxide, methaneand hydrogen chloride, however, the conditionsvary wildly with the microwave oven. For mostpurposes, the In-Syringe or LeBlanc methods givemore reliable results.

Part 6. Advanced GasesThe two gases described here are produced by theIn-Syringe method. The preparation of these gasesand the experiments that go with them should beconducted by individuals familiar and experiencedwith gas production using the In-Syringe method.These two gases are considered ‘‘advanced gases’’ fordifferent reasons. Silane is an extremely pyrophoricgas and great caution must be exercised to preventunintentional fires. For hydrogen sulfide, it is itsoffensive odor and high toxicity that warrant the

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Octubre de 2005 127

‘‘advanced’’ classification. Use of a fume hood isadvised with both gases.

A. Preparation of Silane and ExperimentsList of Experiments:

1. Silanes react with air 2. Silane reacts with oxygen 3. Silane reacts with chlorine 4. Thermal decomposition of silane 5. Reaction with aqueous potassium hydroxide

B. Preparation of Hydrogen Sulfide andExperiments List of Experiments:

1. Hydrogen sulfide is slowly oxidized 2. Hydrogen sulfide is a weak acid 3. Reaction between hydrogen sulfide and

aqueous sodium hydroxide 4. Hydrogen sulfide burns in oxygen with a

howling blue flame 5. Reaction between hydrogen sulfide and

sulfur dioxide yields elemental sulfur 6. Metal sulfide precipitation reactions 7. Oxidation of metal sulfides

Our Microscale Gas Chemistry WebsiteOur gas book, numerous color photographs of pro-cedures, experiments and demonstrations, a fewQuickTime movies of techniques and experimentsare available on the web at our microscale gas chem-istry website. Equipment ordering information andhistorical information are also available at the site.Use of the site is free.http://mattson.creighton.edu/Microscale_Gas_Chemistry.html

References

Books and Special PublicationsBailey, G. H., Snellgrove, D. R., Intermediate Inorganic Chemistry, Vol

1. Non-metals, University Tutorial Press, Ltd., London, 1929.Brownlee, R., Hancock, W., Fuller, R., Sohon, M., Whitsit, J., First

Principles of Chemistry, Allyn and Bacon, New York, 1931.Fownes, G., Elementary Chemistry, Theoretical and Practical, Lea &

Blanchard Publishers, Philadelphia, 1845.Gibbs, F. W., Joseph Priestley, F. W. Doubleday & Company, Inc.,

Garden City, New York; 1967.

Kometz, A., Moderne Energietechnologien, Martin-Luther-Universitat,Halle-Wittenberg, Germany, 2001.

Leicester, Henry M. The Historical Background of Chemistry, DoverPublications, Inc., New York, 1971.

Mattson, B., Anderson, M., Mattson, S., Microscale Gas Chemistry,3rd Edition, Educational Innovations, 2003.

Partington, J. R., A Short History of Chemistry, Harper and Brothers,New York, 1937.

Priestley, J., Experiments and Observations on Different Kinds of Air.3 vols. London, 1775.

Remsen, I., An Introduction to the Study of Chemistry, Henry Holtand Company, New York, 1886.

Slater, A., Rayner-Canham, G., Microscale Chemistry LaboratoryManual; Addison-Wesley Publishers Limited, 1994.

Electronic References:Menzel, P., ‘‘MedTech-Set LMP 1: Schülerversuche mit Medizin-

technik-Zubehör: der einfache Umgang mit Gasen’’,http://www.hedinger.de/schule/d_produkt_detail. asp?id=61, last

electronic access 11 May 2005.Obendrauf, V., ‘‘Experimente mit Gasen im Minimastab’’, Chemi-

cal Education Journal,http://chem.sci.utsunomiya-u.ac.jp/v7n2/angela/angela_abstract.html, last electronic access 11 May 2005.

Singh, M., Szafran, Z., Pike, R., ‘‘National Microscale ChemistryCenter’’, http://www.microscale.org/, last electronic access11 May 2005.

Journal ArticlesAlyea, H. N., ‘‘Syringe Gas Generators,’’ Journal Chemical Educa-

tion, 69, 65 (1992)Choi, M., ‘‘Microscale Chemistry in a Plastic Petri Dish: Prepara-

tion and Chemical Properties of Chlorine Gas’’, JournalChemical Education, 79, 992-993, 2002

Eggen P. O.; and Kvittingen, L., ‘‘A Small-Scale and Low-CostGas Apparatus for the Electrolysis of Water’’, Journal Chemi-cal Education, 81, 1337-1338, 2004

Ibáñez, J. G.; Alatorre-Ordaz, A.; Mayen-Mondragon, R.; Mo-ran-Moran, M. T.; Mattson, B.; Eskestrand; S., ‘‘LaboratoryExperiments on the Electrochemical Remediation of theEnvironment, Part 7. Microscale Production of Ozone’’,Journal of Chemical Education; Month, 2005.

Ibáñez, J. G.; Navarro-Monsivais, C.; Terrazas-Moreno, S. Mena-Brito, R.; Pedraza-Segura, L; Mattson, B.; Hoette, T., ‘‘Mi-croscale Environmental Chemistry Part 4. Production ofClO2, an environmentally-friendly oxidizer and disinfec-tant’’, The Chemical Educator; Month, 2005.

Kilroy, J., Orna, M. V., ‘‘Small-Scale Controlled Gas GenerationBasket’’, Chemunity News, IV, No. 3, November, 1994, p. 16.

Kvittingen, L.; and Verley, R., ‘‘Construction of a Small-Scale andLow-Cost Gas Apparatus’’, Journal Chemical Education, 81,1339-1340, 2004.

Wang, J.; Lu, Z.; and Zhao, C, ‘‘A Novel Microscale Gas Gener-ator’’, Journal Chemical Education, 80, 181-182, 2003.

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Microscale Gas Chemistry