Experiments with Nitrous Oxide
Patrick Sullivan, Jiro Fujita, Kayla Pound, Wes Cheng and Scot Eskestrand
Department of Chemistry, Creighton University
Omaha, Nebraska 68178 USA
Bundesoberstufenrealgymnasium Feldbach, Austria
Our series on microscale gas chemistry published in Chem13 News began in October, 1996. To date we have published simple methods for the safe generation of seventeen different gases with the use of plastic syringes. Each article also contains up to ten microscale experiments for the topic gas. Many of these can be directly used in the high school or college classroom as demonstration experiments or laboratory activities. The entire series is also available at our website2 in edited form along with color photographs of many of the experiments.
Nitrous oxide Background
The official IUPAC name for nitrous oxide, N2O, is dinitrogen oxide. Like many substances, N2O has a common name, ‘nitrous oxide’ which is so widely used that most people refer to the gas by its common name. The gas was discovered by Joseph Priestley and described in his 1772 paper titled “Observations on Different Kinds of Air.” In this paper, he called the gas ‘nitrous air diminished.’ It is also referred to as simply ‘nitrous’ or 'laughing gas' and is the chemical subject of the famous cartoon of a program at the Royal Society in the early 19th century.
Figure 1. James Gillray's 1802 caricature of a lecture on at the Royal Institution titled, "New Discoveries in Pneumaticks: or, an Experimental Lecture on the Power of Air."3
(Reproduced courtesy of the Library and Information Centre, Royal Society of Chemistry.)
Nitrous oxide is a colorless gas with a slightly sweet odor. It is the least reactive of all the nitrogen oxides at normal temperatures — it does not even react with the halogens. At higher temperatures it functions as an oxidant. Nitrous oxide is fairly soluble in a wide variety of solvents including water, alcohols and sulfuric acid. The gas is also soluble in fats/oils, which coupled with the fact that N2O is a condensable gas, makes the gas an ideal propellant for whipping cream. Nitrous oxide is used as an inhalation anesthetic and analgesic.
Physical Properties of Nitrous Oxide, N2O
Molar mass: 44.0128 g/mol
Odor: slightly sweet
melting point -90.81 oC
boiling point -88.46 oC
density: 1.799 g/L at 25 oC and standard pressure
density of N2O : density of air = 1.52 : 1.00
solubility: 56.7 mL/100 mL at 25 oC and standard pressure;
very soluble in alcohols, ether, oils and sulfuric acid
DHf = +82 kJ
General Safety Precautions. Always wear safety glasses. Gases in syringes may be under pressure and could spray liquid chemicals. Follow the instructions and only use the quantities suggested.
Toxicity. Nitrous oxide has relatively low toxicity, nevertheless it is an asphyxiant. Its anesthetic and analgesic effects are not noticed when working with small quantities of the gas.
Suitability. All of these experiments are suited for use as classroom demonstrations and laboratory activities. Individuals attempting these experiments should be experienced with the simpler syringe/gas techniques.
Equipment Required.4 The following equipment can be ordered from a variety of vendors. The following equipment is referred to in this article
• several 60-mL plastic syringes with a LuerLOK fitting
• syringe cap fittings, latex LuerLOK
• latex tubing: 1/8-inch (3.175 mm) ID, 2-cm and 15-cm lengths
• hemostat, plastic
•test tube, 18 x 150 mm, equipped with a two-hole #1 rubber stopper; the holes of the rubber stopper are each equipped with a 4-cm length of glass tubing (5 mm OD)5
• silicone oil or spray (silicone spray is sold in hardware stores; Educational Innovations, $5.95 Part #GAS-150)
• ring stands (2) and three-prong clamps (2)
• Bunsen burner
• Gas Reaction Catalyst Tube6
Preparation of Nitrous Oxide.
Traditionally, nitrous oxide is made by the thermal decomposition of ammonium nitrate at temperatures between 170 - 260 oC.7 This method was developed by the French chemist Claude Louis Berthollet in 1785 and has been widely used ever since. Unfortunately, the method poses a potential explosion risk from overheating ammonium nitrate. Here we follow a less familiar method that gives excellent results and poses no risk of explosion. Gently heating a dilute nitric acid solution of ammonium nitrate in the presence of small amounts of chloride gives almost pure N2O.8 The reaction is:
NH4NO3(aq) N2O(g) + 2 H2O(l)
The heating can be done in a test tube or a hot
water bath. Both methods are described here.
Nitrous oxide is produced by the general thermal method used in previous parts of this series. The assembled apparatus is shown in Figure 2.
Figure 2. Apparatus
Nitrous oxide by the traditional thermal method.
To assure that the syringe plunger can move easily in the barrel, a thin film of silicone oil or spray is applied to the groove in the plunger's rubber seal. A small burner is also needed. The left syringe, labeled 'N2O' is used to collect relatively pure N2O(g) and the syringe labeled 'Waste' is used to collect impure samples of gas and unwanted air. A pinch clamp or hemostat is used to pinch closed one of the latex tubes.
Start by pinching closed the syringe labeled ' N2O'. Place 5 mL 6 M HNO3, 1 g NH4NO3 and 0.05 g NaCl into the medium (18 x 150 mm) test tube. Insert the stopper firmly in order to form an air-tight seal. Caution: Do not crimp the latex tubing!
Nitrous oxide is generated by the following 3-step maneuver.
It is possible (and probably desirable) to replace the N2O(g) syringe with a clean, dry syringe, and repeat Steps 2 and 3; numerous syringefuls of N2O can be collected in this fashion. As each N2O-filled syringe is removed from the apparatus, cap the syringe with a latex syringe cap. After several syringefuls of N2O have been collected, allow the apparatus to cool.
|Boiling Water Bath Method.
Before starting, prepare a hot water bath at a continuous boil. In a small clean test tube, measure out 0.05 g NaCl and 1.0 g NH4NO3. Measure out 5 mL of 6 M HNO3 and add to the test tube. Gently swirl the mixture until all of solid is completely dissolved. Transfer mixture to a small weighing boat. Lubricate a 60 mL syringe and draw the liquid mixture from the weighing boat. Cap the syringe and place in boiling hot water bath. It will take about 20 - 30 minutes to completely fill a syringe with N2O by this method.
Nitrous oxide being made in a boiling water bath.
• Nitrous oxide cartridges, available from restaurant supply houses9
• CO2-bicycle tire pump10
• a glass marble (15 mm dia)
• 5 washers (18 mm dia washers)
• Dremel tool
• latex tubing, 3 cm length
• 1-mL plastic disposable syringe
The cartridge method requires a little more initial effort, but provides for a very inexpensive and reliable method for quickly dispensing N2O. One dispenser is adequate for an entire laboratory class of students. Nitrous oxide is sold as a propellant for whipping cream. Each nitrous cartridge contains approximately 7 g (160 mmol) N2O — enough to fill over 60 syringes with 60-mL N2O. The ‘nitrous’ cartridges are shaped similar to CO2 cartridges used for inflating bicycle tires, however, they are a bit shorter and the connection tip is a bit wider. For those two reasons, the bicycle tire pump must be modified slightly in order to accept nitrous cartridges. Because the overall length of the CO2 cartridge is longer than the N2O cartridge, a glass marble plus a few washers (we use several washers with a combined thickness of 8 mm) are placed in the pump body as shown in Figure 3. Next, the inner threads of the brass head piece need to be removed with a Dremel tool so that the wider nitrous connection top will fit into the head. Use caution not to damage either the piercing cannula or the O-ring at the base of the threads during the thread-removal procedure. This work area is shown in Figure 4.
Figure 3. Bicycle tire pump modified to dispense N2O(g).
Figure 4. Bottom of head piece of bicycle tire pump. The threads on the inside of the brass fitting must be removed.
Nitrous Oxide being collected by modified bicycle tire pump
When installing the cartridge, use care to not over-tighten the dispenser head which could damage the rubber O-ring. Using the modified dispenser is easy. A 3-cm length of a plastic 1-mL syringe barrel is inserted into the tire-valve fitting of the dispenser forming a gas-tight fit. A short length of latex tubing is slipped over the cut-off syringe and the dispenser is ready for use. This tubing can connect directly to the LuerLOK fitting of a syringe to be filled with the gas. Pulling back on the handle for just a brief instant is enough to fill a syringe with 60-mL N2O. Figure 5 shows comparative gas chromatograms of N2O produced by the three methods described above.
Disposal. Unwanted samples of N2O(g) may be discharged into the room or outdoors.
Other gases. In
several of these experiments, other gases are called for. Instructions
for the preparation of these gases is available at our website2
or in our books.11
Experiment 1. Wooden Splint
test for Nitrous Oxide.
|Nitrous oxide is the only common gas, other than oxygen, that will ignite a glowing splint. Remove the latex syringe cap and set it aside. Connect the syringe to a glass pipet with a short length of latex tubing as shown in Figure 6. Ignite and then blow out the wooden splint. While the splint is still glowing, discharge a few mL of N2O directly onto the red embers. The splint will re-ignite.||
Nitrous Oxide re-ignites a glowing splint.
Experiment 2. Nitrous Oxide
forms explosive mixtures with hydrogen.
Prepare a mixture of 50% H2 and 50% N2O in a single syringe. Bubble some of the mixture through a 3% soap solution12 in a plastic weighting boat. Ignite the mixture with a match, which should produce a loud bang. The reaction is:
N2O(g) + H2(g) N2(g) + H2O(g) DH = -324 kJ
Experiment 3. Nitrous Oxide
This experiment is similar to numerous ‘pipet rocket’ experiments we have described throughout this series. For full instructions on the assembly of the piezoelectric sparker and the fueling procedue for the rockets, see our website2 or Experiment 7 in our CHEM13 News article on chlorine.13
Experiment 3A. CH4/N2O
Prepare a mixture of 10-mL CH4 and 40-mL N2O in a single syringe. Displace water in a water-filled cut-off disposable pipet. Slip the pipet over a piezoelectric sparker, replace some water into the stem and ignite the gas mixture with a spark. The rocket will fly over 5 m. An especially bright light accompanies the detonation. The reaction is:
4 N2O(g) + CH4(g) 4 N2(g) + 2 H2O(g) + 2 CO2(g) DH = -1131 kJ
Experiment 3B. H2/N2O
Prepare a mixture of 20-mL H2 and 20-mL N2O in a single syringe. Displace water in a water-filled cut-off disposable pipet. Slip the pipet over a piezoelectric sparker, replace some water into the stem and ignite the gas mixture with a spark. The rocket will fly over 10 m. The detonation is louder than the analogous reaction between methane and nitrous oxide. The reaction is given in Experiment 2.
Experiment 4. Solubility in Water and Oil.
Experiment 4A. Solubility
Nitrous oxide is reasonably soluble in water. Almost 60 mL N2O will dissolve in 100 mL water. Fill a syringe with 20 mL N2O. While the cap is still removed, draw in 40 mL water. This is more than enough water to dissolve all of the gas at 25 oC. Allow the syringe to stand overnight. By morning, almost all (>90%) of the N2O will have dissolved. The solution process can be considerably hastened by positioning the syringe with its Latex cap resting on the countertop and pressing firmly downward. Over the course of several minutes much of the gas will go into solution. Next, remove the gas from solution by pulling the plunger outward to the 60-mL mark. Tap on the syringe and bubbles of N2O will swirl out of solution.
Experiment 4B. Solubility
Repeat Experiment 4A but with vegetable oil instead of water as the solvent. N2O is even more soluble in vegetable oil than it is in water.
This picture shows N20 'degassing' from a solution with vegetable oil. The plunger is being held outward to create a reduced pressure inside the syringe. This picture was taken seconds after the solution was tapped against the countertop in order to initiate bubble formation. The viscosity of the oil provides for a spectacular effect.
|Experiment 5. Magnesium
Burns in Nitrous Oxide.
Support a large (25 x 200 mm) test tube in a vertical position with the aid of a ring stand. Add sand to a depth of 1 - 2 cm in order to protect the bottom of the test tube from the hot burning magnesium. Generate a syringeful of N2O(g). Equip the syringe with a 15-cm length of latex tubing and slowly discharge all 60-mL of the gas just above the surface of the sand as shown in Figure 7. The gas is 37% heavier than air and will displace air upward.
Form a 3-cm length of magnesium ribbon into a loose coil. Using tongs to hold the magnesium, ignite the magnesium with the flame of a Bunsen burner and immediately drop the burning magnesium into the test tube. The Mg ribbon will burn brightly white at first and then turned orange as the N2O nears depletion. A white cloud of MgO(s) will form in the test tube. Allow the test tube to cool, then dump out the sand and unreacted Mg into a beaker. Add 30-mL water and a few drops of phenolphthalein indicator solution to the test tube. Stopper and shake the contents of the test tube. The white suspension of MgO will slowly turn to a pink suspension as MgO slowly hydrolyses to form Mg(OH)2.
Magnesium Burning in Nitrous Oxide
|Experiment 6. The Enlarged
Candle Flame of Nitrous Oxide.
Joseph Priestley described the combustion of a candle in nitrous oxide as enabling the candle to burn with an “enlarged flame.” As the discoverer of oxygen, he was familiar with the dazzling combustion of a candle in the presence of oxygen. These were the only two gases known to Priestley that could facilitate combustion. In this experiment, we shall compare air, oxygen and nitrous oxide as oxidants for a candle.
Tape a birthday
candle to a long glass stir rod as shown in Figure 8. Support a large
(25 x 200 mm) test tube in a vertical position with the aid of a ring stand.
Ignite the candle and lower it into the test tube. It will burn for
a few seconds and then go out due to lack of oxygen.
syringeful of N2O(g) and with the aid of a 15-cm length
of latex tubing and slowly discharge all 60-mL of the gas just above the
bottom of the test tube as was done in the previous experiment.
Ignite the candle and lower it to the bottom of the test tube into the
N2O(g). It will burn much longer than in air
and will burn with an enlarged flame as described by Priestley. Next,
generate a syringeful of O2(g) as described at our
website.2 Repeat the candle experiment and notice
the differences in the abilities of the two gases to support combustion.
Candle burning in air-filled test tube.
Candle burning in N2O-filled test tube.
Candle burning in O2-filled test tube.
Experiment 7. Catalytic
Oxidation of Methane with Nitrous Oxide.
The oxidation of methane with N2O does not occur under standard conditions. However, at elevated temperatures and in the presence of a palladium catalyst, the reaction proceeds as given in Experiment 3A.
This reaction is accomplished with a Gas Reaction Catalyst Tube shown in Figure 9. The catalyst tube 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.
Figure 9. Gas Reaction Catalyst Tube
(available from Educational Innovations6)
Lubricate both syringes. Fill the reagent syringe with 40 mL N2O (0.34 mmol O2) and 10 mL methane (0.41 mmol.) Cap the syringe and allow the gases to mix for several minutes. Connect the reagent syringe to the catalyst tube and assemble the apparatus as shown in Figure 9. Both syringes are supported 30-cm above the bench top with the aid of two ring stands and two 3-prong clamps. Pass about 10 mL of gas mixture through the catalyst tube. This will check for leaks, determine that the plunger in the receiver flask moves freely and displace air (or previous gas mixtures) from the catalyst tube. (Option: Remove the receiver syringe from the catalyst tube, discharge the 10-mL air from the receiver syringe and reconnect to the catalyst tube.) With a Bunsen burner on low heat (no sharp inner cone), heat the catalyst tube evenly on all sides for a total of about 30 seconds. The catalyst will become dark, almost black in color when it is ready for use. Remove the heat; it is NOT necessary to continue to heat the catalyst. Slowly pass about half of the CH4/N2O reagent gas mixture through the catalyst tube over the course of about 30 seconds. The catalyst inside the tube may become red hot, in which case you should slow down the flow of gas. Small droplets of water may form on the glass near the receiver syringe. A cloud of condensing water vapor may also be noted in the receiver syringe. After half of the gas mixture has been passed through the catalyst tube, remove the heat. Remove both syringes and cap them with latex syringe caps. Label the syringes with a marker pen.
One or more of the following tests may be performed on the reagent gas mixture and product gas mixture:
(a) Limewater test for CO2: Place 10 mL limewater in a 15 x 180 mm test tube. Equip the syringe with a 15 cm length of latex tubing. Bubble 10 - 20 mL of the gas through the limewater solution. Remove the syringe and tubing. Stopper the solution and shake to mix gaseous layer with limewater solution.
(b) Flammability test: Fill a small weighing boat with 3% dish soap solution.12 Equip the gas syringe with the 15-cm length of latex tubing. Discharge 10-mL gas into the soap solution in order to produce a mound of several large bubbles. Try to ignite the bubbles with a match. If the bubbles contain hydrocarbons, they may burn or pop rather than simply break.
(c) Gas chromatography. We use gas chromatography to separate and detect syringe gases.14 We use a thermoconductivity detector and run the GC at room temperature. Carrier gas is helium, 30-mL/minute.
(d) Test for the presence of water. The inside of the syringe may be coated with minuscule drops of water. These are difficult to see because the syringe is translucent. 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. As chemical confirmation, remove the plunger just long enough to add a piece of blue-colored Drierite15 to the syringe. Return the plunger or stopper the syringe barrel. The presence of water is confirmed if the blue granule turns pink-purple within a few minutes.
Activating the catalyst by heating for 30 seconds.
The catalyst darkens.
The catalyst glows red from this reaction!
Clean-up and Storage.
At the end of the experiments, clean the syringe parts, caps and tubing with soap and water. Use plenty of soap to remove oil from the rubber seal. This extends the life of the plunger. It may be necessary to use a 3-cm diameter brush to clean the inside of the barrel. Rinse all parts with distilled water. Be careful with the small parts because they can easily be lost down the drain. Important: Store plunger out of barrel.
We gratefully acknowledge
Rick Swanson (History of Science and Technology, University of Minnesota)
and Dr. Frank A. J. L. James (Reader in History of Science, The Royal Institution,
London) for their assistance in many of the historical details relating
to Figure 1, including information provided in Footnote 3.
1. Author to whom correspondence should be addressed. E-Mail: email@example.com
2. Website: http://mattson.creighton.edu/Microscale_Gas_Chemistry.html
3. This caricature is discussed in Science as Public Culture by Jan Golinski (Cambridge University Press, 1992). Lecturer is Dr. Thomas Garnett (the Royal Institution's first professor of chemistry) and Sir Humphrey Davy (with the bellows) is the assistant. Count Rumford is standing by the door. Thomas Garnett, as well as several other Edinburgh-educated physicians were followers of Thomas Beddoes and the 'pneumatic medicine movement,' which seemed to be based on chemical research. The medical use of the gas was viewed as radical and distasteful by the established medical community. In fact, Samuel Latham Mitchill (also an Edinburgh-educated physician who studied with Beddoes) claimed the gas was the chemical source of much disease, including the yellow fever that was plaguing Philadelphia and New York. Nevertheless, the use of nitrous oxide remained quite the rage in social circles.
4. Syringes and related equipment can be ordered from a variety of vendors including Educational Innovations, Flinn Scientific (US sales only), Micromole and Fisher Scientific. Part numbers and links to their websites are provided at our microscale gas website (Endnote 2)
5. Insert the glass tubing to a depth of about 1 cm into the stopper; wet the stopper with alcohol, not mineral oil, before inserting the glass tubing.
6. The Gas Reaction Catalyst Tube Kit (includes syringes and tubing) can be ordered from Educational Innovations (sells worldwide); part number # GAS-100, e-mail: firstname.lastname@example.org, website: www.teachersource.com
7. Archibald, E. H., The Preparation of Pure Inorganic Substances, pg 246, Wiley, New York, 1932.
8. Cotton, F. A., Wilkinson, G., Advanced Inorganic Chemistry, Fourth Edition, pg.,423, Wiley, New York, 1980.
9 “Cream Charger” cartridges (UPC 85355 00088) are available from iSi North America, Inc., Telephone 1-800-211-9608
10 The carbon dioxide cartridge bicycle tire pump (sold as ‘Ultraflate’) is available from bicycle supply stores for about $20. You may purchase the Untraflate (UPC 08162 02410) from Innovations in Cycling, Inc., Tucson, AZ, 1-520-295-3936.
11 (a)The Chemistry of Gases, A Microscale Approach, Mattson, B. M., Anderson, M. P., Schwennsen, Cece, Flinn Scientific, 1999, ISBN #1-877991-54-6 (This book is also available from Mircomole 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.
12 Dish soap solution, 3%, is prepared by dissolving 3 g dish soap per 100 g distilled water.
13 “Microscale Gas Chemistry, Part 10. Experiments with Chlorine” Mattson, B. M.; Harrison, B.; Lannan, J., Chem13 News, Number 260, October, 1997.
14 Our choice of column is a Porapak N 80/100, 6-ft (180 cm), inside diameter = 0.085 inches (2.2 mm) available from Alltech Part Number 2716; telephone: 847-948-8600
15 anhydrous CaCl2 granule coated with
blue indicator that turns pink in the presence of water; Fisher 07-578-3A
Pat Sullivan presenting the Gas Reaction Catalyst Tube at Creighton's St. Albert's Day, November, 2000.
(last updated 24 January 2002)