Demonstrating Heterogeneous Gas-Phase Catalysis with the Gas

Examples of these reactions can be found in many, but not all, of the popular books on chemi- cal demonstrations as well as in this Journal. In this a...
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In the Classroom edited by

Tested Demonstrations

Ed Vitz Kutztown University Kutztown, PA 19530

Demonstrating Heterogeneous Gas-Phase Catalysis with the Gas Reaction Catalyst Tube submitted by:

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Bruce Mattson,* Jiro Fujita, Rebecca Catahan, Wes Cheng, Jaclyn Greimann, Trisha Hoette, Paras Khandhar, Andrew Mattson, Anand Rajani, and Patrick Sullivan Department of Chemistry, Creighton University, Omaha, NE 68178-0104; *[email protected] Ron Perkins Educational Innovations, Inc., 362 Main Avenue, Norwalk, CT 06851

checked by:

Thomas P. Gonnella Department of Chemistry, Mayville State University, Mayville, ND 58257

Gas-phase reactions involving heterogeneous catalysts have been used in chemical demonstrations for decades. These reactions include: open-container catalyzed reactions of gas mixtures (1–6), reactions that use a catalyst to trigger an explosion of a gas mixture (1), and continuous flow reactions requiring a catalyst (3, 7–9). Examples of these reactions can be found in many, but not all, of the popular books on chemical demonstrations as well as in this Journal. In this article we describe a heterogeneous palladium catalyst suitable for demonstrating continuous-flow, closedsystem gas-phase reactions in the classroom or teaching laboratory. The gas reaction catalyst tube, shown in Figure 1, consists of an extremely thin coating of palladium atoms dispersed over a square tube-shaped ceramic support. The catalyst-coated ceramic support is housed in a borosilicate glass tube (10-mm i.d.) with a net volume of 7–8 mL. The device can be constructed from a used automotive catalytic converter or purchased. The gas reaction catalyst tube can be used to demonstrate a wide variety of gas-phase reactions, including the nine reactions described in this article. They include air or oxygen oxidation of methane, carbon monoxide, and ammonia; hydrogenation of alkenes; thermal decomposition of nitrous oxide; and reactions involving oxidation by nitrous oxide and nitrogen dioxide. Several of the reactions demonstrate pro-

Figure 1. The gas reaction catalyst tube supported between two ring stands (not shown). This image is also featured in color on the cover.

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cesses that occur in an automotive catalytic converter. In all cases, the products can be tested by simple chemical methods. Equipment Required1 •

Gas reaction catalyst tube, commercially available or constructed from a used automotive catalytic converter; see Supplemental Materials for instructionsW

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Syringes, 60-mL plastic syringe with a LuerLOK fitting

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Syringe cap fittings, Latex LuerLOK

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Latex tubing, 1/8-in. (3.175 mm) i.d., 2-cm and 15cm lengths

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Two ring stands with one three-prong clamp each (optional)

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Bunsen burner

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Silicone oil

In addition, the various chemical tests of the gaseous products require equipment and chemicals not listed above but are described later in the section on confirmatory tests. Gases The gas-catalysis experiments described here require samples of various gases. Compressed gas cylinders are convenient and the purity is assumed to be quite good. Connect the syringe (plunger fully inserted) directly to the gas regulator with a short length of rubber tubing or equivalent. Adjust the pressure to 100 kPa (1 atm, 15 psi) using the gas-regulator knob. Use the flow valve to slowly discharge the desired amount of gas into the syringe. Natural gas can be used as a source of methane. Fill the syringe as described above, however, the pressure of the natural gas line is not enough to push the plunger outward without some assistance. All of the reagent gases in this article can be prepared by simple methods described in Chem13 News (10). These gas preparations are also available in two books (11) and at a Web site.2 Gases prepared in this method contain small amounts of air.

Journal of Chemical Education • Vol. 80 No. 7 July 2003 • JChemEd.chem.wisc.edu

In the Classroom

Toxicity Manipulating gases in syringes is generally safe, and unintentional discharges are not common. Nevertheless, such discharges are possible and it is important to read and understand the following information. Nitrogen dioxide has an irritating odor and is a poisonous gas. Concentrations of 100 ppm and higher are dangerous. To put this in perspective, if the contents of one entire syringe of NO2 (60 mL) were discharged into a volume of 1 m3, the concentration of NO2 would be 60 ppm. Ammonia has a pungent irritating odor and is highly poisonous. Although less toxic than ammonia and nitrogen dioxide, carbon monoxide is toxic but has no odor. Symptoms of carbon monoxide poisoning include headache, mental dullness, weakness, nausea, and vomiting. Exercise caution when working with poisonous gases; vacate areas that are contaminated with unintentional discharges of gas. The Apparatus

Setup The assembled apparatus is shown in Figure 1. Two short pieces (approximately 2-cm) of Latex tubing connect the catalyst tube to the two syringes. The syringe on the left contains the reagent gas mixture to be passed through the catalyst. The plunger of the receiver syringe (right) must be able to move freely in the syringe barrel because it should move outward on its own as the plunger of the reactant syringe is pushed inward. This is assured by lubricating the black rubber plunger diaphragm with silicone oil. The plunger of the receiver syringe should be pulled slightly outward so that the rubber diaphragm is not resting on the bottom of the barrel—this allows the initial outward movement of the plunger to commence at a lower positive pressure. Two ring stands and clamps hold the two syringes in the appropriate position so the gas catalyst reaction tube is positioned above the Bunsen burner’s flame. The clamps should not hold the syringes tightly and must allow free rotation of the syringes and catalyst tube for even heating. With some experience, it is easier to hand-hold the syringes instead of using ring stands. CAUTION! Explosion Risk! Always wear safety glasses! The use of a blast shield is also recommended. The oxidation of methane described in this article utilizes air as a source of oxygen. Do NOT attempt these catalysis reactions using oxygen instead of air: an explosion could result! When attempting reactions other than those described in this article, consider the possibility that the mixture may explode upon contact with heat or the catalyst. For example, both N2O and NO2 form explosive mixtures with H2. If attempting new reactions, start with gas mixtures that have been diluted with an inert gas such as argon or nitrogen and use a blast shield. Heating the Catalyst Tube Heat from a Bunsen burner flame is capable of softening the glass of the catalyst tube. When the glass is soft, it is susceptible to deformations and even “blow holes” if the pressure inside the system is increased by moving the plunger of the syringe. To prevent overheating the glass, use a gentle Bunsen burner flame: minimize the amount of air used so

that the flame has a soft, ill-defined blue inner cone. Position the catalyst tube at least 1 cm above the tip of the inner cone. Watch for traces of red, orange, or yellow in the flame above the catalyst tube. These colors indicate that the glass is softening. If softening should happen, remove the tube from the flame and make adjustments to the flame.

Activating the Catalyst The ceramic catalyst will appear tan or brown until it is activated. “Activation” simply involves purging the tube with 50 mL of air to remove gases present from previous experiments and then heating the catalyst tube in a cool flame until it starts to turn black owing to the presence of elemental palladium. (Catalyst tubes constructed from automotive catalysts will darken, but will not turn black.) Heat the catalyst tube evenly by rotating the syringes periodically in the flame. Using a thermocouple, we have estimated the temperature inside the catalyst tube to be 350–400 ⬚C when the color of the catalyst darkens. If nitrogen or argon is available, it is better to purge the catalyst tube with either of these gases during the activation step. In this case, purge the tube with the gas after the catalyst is hot. Activating the catalyst takes less than a minute and can be done as part of the experiment. Cleanup and Storage After completing the reactions, heat the catalyst for 30 seconds in the flame, remove the tube from the flame, and purge the catalyst with a syringe filled with an inert gas such as nitrogen or argon. Air may be used if inert gases are not available. Allow the catalyst to cool. Store the gas reaction catalyst tube in a sealed plastic bag. Clean the syringes with soap and water. Be sure to remove all of the silicone lubricant as it will deteriorate the plunger’s rubber seal. To improve the syringe’s lifetime, store the plunger out of the barrel. Catalyzed Gas Reactions

Empty Reaction Tube To Test the Role of the Catalyst To prove the role of the catalyst in these reactions, it may be desirable to perform these reactions with an empty reaction tube, similar in design to the gas reaction catalyst tube but without the catalyst. In each of the reactions below, we have established that the reactants pass through the empty control tube without reacting. Use extreme caution when attempting these reactions with an empty control tube! The catalyst provides a lower energy pathway by which a steady reaction occurs; without the catalyst present, the gases may undergo a thermal explosion if overheated. All of the reactions below were run with a empty reaction tube without incident, but it is still recommended that a blast shield be used when attempting any reaction with an empty reaction tube. Reaction 1. Catalytic Oxidation of Methane with Air CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

∆H = ᎑803 kJ

Fill the reagent syringe with 50 mL of air (0.4 mmol of O2) and 10 mL of methane (0.4 mmol). Connect both the reagent and receiver syringes to the catalyst tube and assemble the apparatus as shown in Figure 1. Pass about 10 mL of gas mixture through the catalyst tube to check for leaks, deter-

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mine that the plunger in the receiver flask moves freely, and displace air from the catalyst tube. (Option: Disconnect the receiver syringe from the catalyst tube, discharge the 10 mL of contents from the receiver syringe, and reconnect to the catalyst tube.) Heat the catalyst tube gently and evenly on all sides for a total of about 30 seconds. With continued heating in a cooler flame (move tube to the top of outer cone or use less make-up air), slowly pass about half of the methane兾air reagent gas mixture through the catalyst tube over the course of about 30 seconds. The volume of gases collected in the receiver syringe should approximately equal the volume decrease in the reagent syringe because the main component in the syringe is nitrogen from the air. After half of the gas mixture has been passed through the catalyst tube, remove the tube from the heat. Remove both syringes and cap them with Latex syringe caps. Label the syringes ‘reactants’ and ‘products’ with a marker pen. Perform one or more of the following tests, all described below, on the reagent gas mixture and product gas mixture: (a) limewater test for CO2, (b) flammability test, (c) gas chromatography, and (d) water test. More information about this experiment along with color photographs can be found at the gas chemistry Web site.2 This reaction has been described by Cooper and Wolf (7) and utilizes a Bunsen burner and a platinum wire.

Reaction 2. Catalytic Oxidation of Carbon Monoxide with Air or Oxygen 2CO(g) + O2(g) → 2CO2(g)

∆H = ᎑566 kJ

In this oxidation, either air or oxygen may be used as the oxidant. Follow the general procedure described in reaction 1 for methane. Use 45 mL of air (0.38 mmol of O2) and 15 mL of carbon monoxide (0.6 mmol) or 20 mL of O2 (0.8 mmol) and 40 mL of CO (1.6 mmol). The limewater test for CO2 or gas chromatography performed on the reagent gas mixture and the product gas mixture will help characterize the reaction. If O 2 is used rather than air, the flammability and glowing splint tests may be performed. If performing the reaction with a control (empty) tube, use air, not oxygen.

Reaction 3. Hydrogenation of Ethene C2H4(g) + H2(g) → C2H6(g)

∆H = ᎑137 kJ

Fill the reagent syringe with 30 mL of ethene (1.2 mmol) and 30 mL of hydrogen (1.2 mmol). Connect the reagent and receiver syringes to the catalyst tube as shown in Figure 1. Pass about 10 mL of the gas mixture through the catalyst tube to purge it of air. Remove the receiver syringe, discharge the air, and then reconnect it as quickly as possible in order to minimize H2 loss. Heat the catalyst tube evenly on all sides for about 30 seconds, then slowly pass about half of the C2H4兾H2 reagent gas mixture through the catalyst tube over the course of about 30 seconds. The volume of gases collected in the receiver syringe should be less than the volume decrease in the reagent syringe; 2 mol of gaseous reactants become 1 mol of gaseous products if the reaction efficiency is 100%. In our experience, these experimental conditions cause hy-

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drogenation with about 50% efficiency. Nearly complete hydrogenation can be achieved by activating the catalyst tube in a gentle flame with pure hydrogen (60 mL) prior to passing the mixture through the catalyst tube. After half of the gas mixture has been passed through the catalyst tube, remove the tube from the heat. Remove both syringes and cap them with Latex syringe caps. Label the syringes ‘reactants’ and ‘products’ with a marker pen. The bromine–water test for C2H4 should confirm that there is less ethene in the product syringe than in the reactant syringe. Gas chromatography allows for a quantitative estimation of the extent of hydrogenation.

Reaction 4. Catalytic Oxidation of Ammonia with Oxygen 4NH3(g) + 3O2(g) → 2N2(g) + 6H2O(g)

∆H = ᎑1268 kJ

This reaction has been the subject of numerous demonstrations involving glowing platinum (3–5) or copper (5). In each case, ammonia and air react at the surface of the metal that has been preheated to redness in a flame. The exothermic nature of the reaction sustains the red glow of the catalyst. In the reaction described here, the palladium catalyst operating at a lower temperature yields nitrogen rather than nitric oxide. Fill the reagent syringe with 30 mL of ammonia (1.2 mmol) and 30 mL of oxygen (1.2 mmol). In this proportion, NH3(g) is the limiting reagent. Connect the reagent and receiver syringes to the catalyst tube as shown in Figure 1. For this reaction, do not pass any of the gas mixture through the catalyst tube to displace air from the tube. Heat the catalyst tube evenly on all sides for a total of about 30 seconds. Slowly pass about half of the ammonia兾oxygen reagent gas mixture through the catalyst tube over the course of about 30 seconds. A cloud or fog of condensing water vapor should be noticed in the receiver syringe. After half of the gas mixture has been passed through the catalyst tube, remove the tube from the heat. Remove both syringes and cap them with Latex syringe caps. Label the syringes ‘reactants’ and ‘products’ with a marker pen. The relative amount of ammonia in each syringe is determined as follows. Note the volume of gas in each syringe. Remove the syringe cap and place each syringe in a 250-mL beaker filled with water. Draw at least 20 mL of water into each syringe; ammonia will quickly dissolve. After a minute, note the new volume of the gas in the syringe. The product syringe will contain little or no ammonia, so the volume of gas will be about the same as its original value. The reactant syringe had contained 50% ammonia so that the volume of gas remaining should be half of its original amount. Add some universal indicator to the discharged water from each syringe in order to estimate the pH. The unreacted ammonia will increase the pH substantially, while the product syringe should remain neutral. If nitric oxide were produced instead of the nitrogen gas, as occurs with the reactions described in the literature (3–5), it would immediately react with oxygen present to form red NO2, an acid anhydride. The red color of NO2 and the low pH of an aqueous solution of the gas would be observed.

Journal of Chemical Education • Vol. 80 No. 7 July 2003 • JChemEd.chem.wisc.edu

In the Classroom

Reaction 5. Catalytic Reaction between Methane and Nitrogen Dioxide CH4(g) + 2NO2(g) → N2(g) + CO2(g) + 2H2O(g) ∆H = ᎑869 kJ

Fill the reagent syringe with 30 mL of methane (1.2 mmol) and 30 mL of nitrogen dioxide (1.2 mmol). This proportion ensures that NO2 is the limiting reagent. The mixture is red-brown owing to the nitrogen dioxide. Connect the reagent syringe to the catalyst tube and assemble the apparatus as shown in Figure 1. Do not pass any of the gas mixture through the catalyst tube to displace air from the tube. Heat the catalyst tube evenly on all sides for a total of about 30 seconds. Slowly pass all of the CH4兾NO2 reagent gas mixture through the catalyst tube over the course of about 30 seconds. The gases collected in the receiver syringe should not be red. Rather, a ‘fog’ of water vapor should be noted. It is possible that the red color will not completely disappear on the first pass. If this occurs, simply reverse directions and pass the gas mixture back through the catalyst in the other direction. In addition to detecting that the reaction has taken place as a result of the disappearance of the red-brown color, the product gases can be tested by the limewater test or the water test. More information about this experiment along with color photographs can be found at the gas chemistry Web site.2 This reaction is highly suited for a lecture demonstration because the red-brown color of the reactants can be seen to disappear while a fog of water forms in the product syringe. (See the cover of this issue for pictures of this reaction.)

Reaction 6. Catalytic Reaction between Carbon Monoxide and Nitrogen Dioxide 4CO(g) + 2NO2(g) → N2(g) + 4CO2(g)

∆H = ᎑1198 kJ

Fill the reagent syringe with 40 mL of carbon monoxide (1.6 mmol) and 15 mL of nitrogen dioxide (0.6 mmol). This proportion ensures that NO2 is the limiting reagent. The mixture is red-brown owing to the nitrogen dioxide. Connect the reagent syringe to the catalyst tube and assemble the apparatus as shown in Figure 1. Do not purge the catalyst tube with the gas mixture before heating. Heat the catalyst tube evenly with a gentle flame on all sides for a total of about 30 seconds. Slowly pass all of the CO兾NO2 reagent gas mixture through the catalyst tube over the course of about 30 seconds. The gases collected in the receiver syringe should not be red-brown. Unlike reaction 5, no ‘fog’ of water vapor will be observed. In addition to detecting the reaction has taken place owing to the disappearance of the red-brown color, the product gases can be tested by the limewater test. This reaction will take place without the catalyst present if high temperatures are used; this can be demonstrated by performing the reaction with a control (empty) tube. Heat the control tube with a larger, hotter flame until the flame begin to take on an orange-yellow color, which results from the sodium in the glass: this is the maximum temperature that the glass can withstand without softening or melting. Slowly pass all of the CO兾NO2 reagent gas mixture through the tube over the course of about 30 seconds. The gases collected in the receiver syringe should not be red-brown.

Reaction 7. Thermal Decomposition of Nitrous Oxide The thermal decomposition of nitrous oxide occurs above 300 ⬚C. The reaction is 2N2O(g) → 2N2(g) + O2(g)

∆H = ᎑164 kJ

Fill the reagent syringe with 60 mL of N2O (2.4 mmol). Connect both the reagent and receiver syringes to the catalyst tube and assemble the apparatus as shown in Figure 1. Pass about 10 mL of N2O through the catalyst tube to displace the air present. Disconnect the receiver syringe from the catalyst tube, discharge the 10 mL of gas from the receiver syringe, and reconnect to the catalyst tube. Heat the catalyst tube evenly on all sides for a total of about 45 seconds. Slowly pass about half of the N2O(g) through the catalyst tube over the course of about 30 seconds. The catalyst may turn slightly tan as a result of oxidation caused by the oxygen produced in this reaction. After half of the gas mixture has been passed through the catalyst tube, remove the tube from the heat. Remove both syringes and cap them with Latex syringe caps. Label the syringes ‘reactants’ and ‘products’ with a marker pen. Test the reagent gas mixture and product gas mixture by the glowing splint test or gas chromatography.

Reaction 8. Catalytic Reaction between Nitrous Oxide and Ammonia 3N2O(g) + 2NH3(g) → 3H2O(g) + 4N2(g)

∆H = ᎑880 kJ

Fill the reagent syringe with 15 mL of ammonia (0.6 mmol) and 45 mL of nitrous oxide (1.8 mmol). In this proportion, NH3 is the limiting reagent. Connect the reagent and receiver syringes to the catalyst tube as shown in Figure 1. Do not purge the catalyst tube with the reaction mixture. Heat the catalyst tube evenly on all sides for a total of about 30 seconds. Slowly pass about half of the NH3兾N2O reagent gas mixture through the catalyst tube over the course of about 30 seconds. After half of the gas mixture has been passed through the catalyst tube, remove the tube from the heat. Remove both syringes and cap them with Latex syringe caps. Label the syringes ‘reactants’ and ‘products’ with a marker pen. Perform the acidity test, ammonia test, or the water test on the reagent gas mixture and product gas mixture.

Reaction 9. Catalytic Reaction between Nitrous Oxide and Carbon Monoxide N2O(g) + CO(g) → CO2(g) + N2(g)

∆H = ᎑365 kJ

Fill the reagent syringe with 30 mL of carbon monoxide (1.2 mmol) and 30 mL of nitrous oxide (1.2 mmol). Connect the reagent and receiver syringes to the catalyst tube as shown in Figure 1. Pass about 10 mL of the gas mixture through the catalyst tube to displace air from the tube. Remove the receiver syringe from the catalyst tube, discharge the contents, and reconnect as before. Heat the catalyst tube evenly on all sides for a total of about 30 seconds. Slowly pass about half of the N2O兾CO reagent gas mixture through the catalyst tube over the course of about 30 seconds. Remove the tube from the heat. Remove both syringes and cap them with Latex syringe caps. Label the syringes ‘reactants’

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and ‘products’ with a marker pen. Perform the limewater and flammability tests or gas chromatography on the reagent gas mixture and product gas mixture. Do not perform the glowing splint test on unreacted N2O兾CO mixture; this mixture of gases reacts explosively.

Trying Other Catalytic Reactions Use caution when attempting other reactions with the catalyst tube. Explosive mixtures, even on the millimole scale are dangerous. When trying reactions for the first time, dilute the gas mixture with an inert gas such as argon or nitrogen. For example, NO2 and H2 react explosively unless diluted. The catalyst glows red and then the explosion occurs. In our case, the plunger shot out of the syringe, but the glass catalyst tube could have just as easily exploded. When new reactions are being explored, they should be done with considerable dilution (perhaps 90% argon and 10% reagents) until the nature of the reaction has been worked out. Never use pure oxygen as an oxidant unless you have determined it is safe to do so. This is done by a series of experiments in which the proportion of O2 is incrementally increased. This approach was used in working with reactions 2 and 4. Generally air can be used as ‘diluted oxygen’; it is approximately 21% O2 and the rest is inert N2 and Ar. Confirmatory Tests for Various Gases

Acidity Test Prepare a universal indicator stock solution by dissolving 5 mL of universal indicator in 50 mL of distilled water. The concentration of the indicator must be fairly high so that the color is readily seen. For each test, transfer 5 mL of the indicator solution into a 15-mm × 180-mm test tube. Equip the reagent and receiver syringe with a 15-cm length of tubing. Discharge 10–20 mL of the gas above the surface of the indicator solution in the test tube. Remove the syringe and tubing. Stopper the test tube and shake the contents to mix gas with solution. Notice color changes. Ammonia Tests Ammonia can be detected by odor. Discharge 3 mL of the gas into an inverted plastic cup (such as a 9-oz or 250mL beverage cup). With a cupped hand, waft the gas from the cup towards your nose. Ammonia can also be detected by the Cu2+ test. Place 5 mL of a 0.10 M CuSO4 solution in a 15-mm × 180-mm test tube. The solution should be a pale blue color. Equip the reagent and receiver syringe with a 15-cm length of tubing. Discharge 10–20 mL of the gas near the surface of the Cu2+ solution. Remove the syringe and tubing. Stopper the test tube and shake to mix the gas with the Cu2+ solution. A deep blue solution indicates the presence of NH3 as a result of the reaction Cu2+(aq) + 4NH3(g) → [Cu(NH3)4]2+(aq)

Bromine–Water Test Prepare a bromine–water solution by mixing chlorine bleach and potassium bromide or sodium bromide (for detailed instructions, see the gas chemistry Web site2). Transfer

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5 mL of dilute bromine–water solution (yellow, not orange) into a 15-mm × 180-mm test tube. Equip the syringe with a 15-cm length of tubing. Bubble 10–20 mL of the gas through the bromine–water solution. Remove the syringe and tubing. Stopper the test tube and shake to mix gaseous layer with bromine–water solution. If alkenes are present, such as ethene, the yellow solution will turn colorless. The reaction is C2H4(g) + Br2(aq) → CH2OHCH2Br(l) + HBr(aq) Other gases, including ethane, CO2, and H2 do not react with the bromine–water solution, so the solution will not discolor.

Flammability Test Prepare a 3% dish soap solution by dissolving 3 g of dish soap in 100 g of water. Fill a small weighing boat with the 3% dish soap solution. Equip the gas syringe with a 15-cm length of tubing. Discharge 10–20 mL gas through the soap solution to produce a mound of large bubbles. Try to ignite the bubbles with a match. If the bubbles contain flammable gas such as hydrogen or hydrocarbons, they should burn or pop rather than simply break. Gas Chromatography Gas chromatography is used to separate and detect gases. A Porapak N 80兾100, 6-ft (180-cm) column3 with an inside diameter of 0.085 in. (2.2 mm) is used with a thermoconductivity detector. The GC is run at room temperature with helium, 30 mL兾min, as the carrier gas. Glowing Splint A traditional test for oxygen is the glowing splint test. Only one other common gas, N2O, is capable of re-igniting a glowing splint. In the traditional test, a wooden splint is ignited, the flame is blown out, and the glowing red end of the splint is thrust into a test tube filled with the gas. The test has been modified to require far less gas: simply discharge 10–15 mL of the gas directly from the syringe onto the glowing splint. The discharge should be done quickly and as close to the glowing splint as possible. Pure O2 and N2O will reignite the splint into an open flame. Mixtures of these gases with other gases may prevent the splint from being re-ignited, however the splint will glow brightly while the gas is being discharged. Limewater Test for CO2 Limewater is a clear, colorless, saturated aqueous solution of Ca(OH) 2 . It is prepared by mixing 1.5 g of Ca(OH)2(s) per liter of water. Stir or shake vigorously and allow the solid to settle overnight. When using limewater, decant carefully to avoid transferring any solid or suspended Ca(OH)2(s). A convenient ‘limewater dispenser’ is described at the microscale gas Web site.2 Place 3–4-mL clear limewater in a 15-mm × 180-mm test tube. Equip the syringe with a 15-cm length of tubing. Discharge 10–20 mL of the gas above the surface of the limewater solution. Remove the syringe and tubing. Stopper the test tube and shake to mix the gas with the limewater solution. A cloudy solution indicates the presence of CO2 as a result of the reaction Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)

Journal of Chemical Education • Vol. 80 No. 7 July 2003 • JChemEd.chem.wisc.edu

In the Classroom

Water Test When water is formed, the product syringe often appears ‘cloudy’ from the aerosol of water. After a few minutes, the aerosol condenses into minuscule drops of water lining the inside of the syringe. By pushing the plunger inward about 5–10 mL and then retracting it back outward by the same amount, the water droplets are pushed along ahead of the plunger. This greatly assists in seeing the droplets. For a chemical confirmation, remove the syringe cap and then the plunger just long enough to add a piece of blue-colored Drierite4 to the syringe. Re-insert the plunger (to the 60-mL mark only) or stopper the syringe barrel. Cap the syringe. The presence of water is confirmed if the blue granule turns pink-purple within a few minutes. Acknowledgments We thank Stan Gross of Creighton University for glassblowing services in the preparation of the catalyst tubes. JG and TH acknowledge support from the Clare Boothe Luce Scholarship Program for Women in Science. TH acknowledges additional support from the Creighton University College of Arts and Sciences Summer Research Stipend for Undergraduate Students. W

Supplemental Material

Information for the construction of the catalyst tube device from a used automobile catalyst and photographs of an automotive catalyst cut in half and segmented is available in this issue of JCE Online. Notes 1. (a) Syringes and related equipment can be ordered from a variety of vendors including Educational Innovations, Flinn Scientific (U.S.-sales only), MicroMole Scientific, and Fisher Scientific. Part numbers and links to Web sites are provided at the microscale gas Web site: http://mattson.creighton.edu/OrderingGasStuff.html (accessed Apr 2003). (b) The Gas Reaction Catalyst Tube Kit can be ordered from Educational Innovations (available worldwide), part number # GAS-100, e-mail: [email protected]; Web site: http://www.teachersource.com (accessed Apr 2003). (c) Silicone oil must be used because it is one of the few lubricants that is not absorbed into the rubber; silicone oil is readily available and is included with the gas reaction catalyst kit sold by Educational Innovations. 2. Microscale Gas Chemistry. http://mattson.creighton.edu/ Microscale_Gas_Chemistry.html (accessed Apr 2003). 3. Available from Alltech, Part Number 2716, http:// www.alltechweb.com/US/Home.asp (accessed Apr 2003). 4. Drierite is an anhydrous CaCl2 granule coated with blue indicator that turns pink in the presence of water. This is available from Fisher Scientific (07-578-3A).

Literature Cited 1. Battino, Rubin; Letcher, Trevor M.; Rivett, Douglas E. A. J. Chem. Educ. 1993, 70, 1029. Gross, G. R.; Bilash, B., III; Koob, J. K. A Demo A Day, A Year of Chemical Demonstrations; Flinn Scientific: Batavia, IL, 1995; pp 190–191. 2. Gross, G. R.; Bilash, B., III; Koob, J. K. A Demo A Day, A Year of Chemical Demonstrations; Flinn Scientific: Batavia, IL, 1995; p 210. 3. Gross, G. R.; Bilash, B., III; Koob, J. K. A Demo A Day, A Year of Chemical Demonstrations; Flinn Scientific: Batavia, IL, 1995; p 224. 4. Shakhashiri, B. Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry; University of Wisconsin Press: Madison, WI, 1985; Vol. 2, pp 214–215. 5. Gilbert, G. L.; Alyea, H. N.; Dutton, D.; Dreisbach, D. Tested Demonstrations in Chemistry and Selected Demonstrations from the Journal of Chemical Education; Division of Chemical Education: Easton, PA, 1994, Vol. I, pp I34–35. 6. Volkovich, Vladimir A.; Griffiths, Trevor R. J. Chem. Educ. 2000, 77, 177. 7. Gilbert, G. L.; Alyea, H. N.; Dutton, D.; Dreisbach, D. Tested Demonstrations in Chemistry and Selected Demonstrations from the Journal of Chemical Education; Division of Chemical Education: Easton, PA, 1994, Vol. I, pp I3 –35, I37. 8. Raymundo-Piñero, E.; Cazorla-Amorós, Diego; Morallón, E. J. Chem. Educ. 1999, 76, 958. 9. Gilbert, G. L.; Alyea, H. N.; Dutton, D.; Dreisbach, D. Tested Demonstrations in Chemistry and Selected Demonstrations from the Journal of Chemical Education; Division of Chemical Education: Easton, PA, 1994; Vol. II, p M64. 10. Preparation of gases: (a) Mattson, B. M. Chem13 News, 1996, 253, 9–12 (hydrogen). (b) Mattson, B. M.; Lannan, J. Chem13 News, 1997, 254, 6–8 (oxygen). (c) Mattson, B. M.; Lannan, J. Chem13 News, 1997, 255, 6–8 (nitrogen dioxide). (d) Mattson, B. M. Chem13 News, 1997, 256, 4–5 (ammonia). (e) Mattson, B. M.; Anderson, M. P.; Catahan, R.; Bansal, M.; Khandhar, P.; Mattson, A.; Rajani, A.; Obendrauf, V.; Vaitkus, R. Chem13 News, 1999, 274, 10–15 (carbon monoxide). (f ) Mattson, B. M.; Hulce, M.; Fujita, J.; Anderson, M. P.; Catahan, R.; Bansal, M.; Khandhar, P.; Mattson, A.; Rajani, A.; Worth, L.; Obendrauf, V. Chem13 News, 1999, 277, 6–11 (ethane). (g) Mattson, B. M.; Catahan, R.; Nguyen, J.; Patel, A.; Khandhar, P.; Mattson, A.; Anand Rajani, A. Chem13 News, 2000, 284, 12–18 (methane). (h) Mattson, B.; Sullivan, P.; Fujita, J.; Pound, K.; Cheng, W.; Eskestrand, S.; Obendrauf, V. Chem13 News, 2002, 299, 15–19 (nitrous oxide). 11. (a) Mattson, B. M.; Anderson, M. P.; Schwennsen, Cece.The Chemistry of Gases, A Microscale Approach; Flinn Scientific: Batavia, IL, 1999, ISBN #1-877991-54-6 (This book is also available from Micromole and is the only source for customers outside the USA). (b) Microscale Gas Chemistry; Educational Innovations, 2000, catalog #BK-590, ISBN #0-9701077-0-6.

JChemEd.chem.wisc.edu • Vol. 80 No. 7 July 2003 • Journal of Chemical Education

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