Experiments with Ethene
Link to C2H4 data page including physical properties.
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.
Ethene has low toxicity. It is flammable and care must be taken to avoid unintentional contact with sparks or open flames. Ethene forms explosive mixtures with air between the ranges of 3 - 30% ethene. Concentrated sulfuric acid is used to prepare ethene; extreme care must be taken when handling concentrated sulfuric acid.
All of these experiments are suited for use as classroom demonstrations. Because the techniques described herein are more advanced than those used in the first ten parts of this series, individuals attempting these experiments should be experienced with the simpler syringe/gas techniques. These experiments are not generally advised for use as laboratory experiments conducted by typical high school students. Advanced students or students with special laboratory skills could be allowed to perform these experiments under close supervision by the instructor.
We recommend lubricating the black rubber diaphragm of the plunger with silicone spray (available from hardware stores) or medium-grade silicone oil (Educational Innovations, $5.95 Part #GAS-150; Fisher Catalog Number S159-500; $34/500 mL.)
Equipment. (This equipment can be ordered from a variety of vendors including Educational Innovations, Flinn Scientific (US sales only), Micro Mole, and Fisher Scientific. Part numbers and links to their websites are provided.)
- several 60-mL plastic syringes with a LuerLOK fitting
- Latex LuerLOK syringe cap fittings
- Small plastic weighing boats
- balance capable of measuring to 0.01 g
- two pieces, latex tubing, 1/8-inch (3.175 mm) ID, 5 cm lengths
- two 18 x 150 mm test tubes
- two-hole #1 stopper fitted with two short lengths (2 cm) of glass tubing
- pinch clamp or hemostat
- ring stand and three suitable clamps to hold test tube and syringes
- small Bunsen burner
- matches or a lighter
- ‘permanent’ marker pen
1 mL concentrated sulfuric acid 1 mL anhydrous alcohol 3 - 5 g polyethylene (for Method II; may be obtained from a plastic milk jug)
Preparation of Ethene. Method I. Dehydration of Ethanol.
The gaseous ethene (C2H4) samples used in these experiments are generated by the Thermal Method described here. The general idea for this method was first proposed by LeBlanc in the 18th century (LeBlanc, Dictionary of Chemistry, Wurtz, 1875). Our modification utilizes clean, dry 60-mL syringes. Multiple syringefuls of C2H4 can be collected during this procedure. Short lengths of glass tubing are inserted through a suitable (#0 or #1) two-hole stopper. Position the stopper snugly into a 120 x 15 mm test tube. The two syringes are connected via 3 - 5 cm pieces of latex tubing to the glass tubes. The assembled apparatus is shown in Figure 1.
Figure 1. C2H4 Generator
Syringe plungers should move easily in the barrels. This can be facilitated by applying a drop or two of silicone oil or spray to the groove in the plunger's rubber seal. A small burner is also needed. The left syringe, labeled 'C2H4' is used to collect relatively pure C2H4(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 'C2H4'. Place a boiling chip in the test tube. Add 1 mL concentrated H2SO4 and 1 mL (2.4 g; 51 mmol) anhydrous ethanol in the test tube. A few bubbles will start to form and the test tube will become too hot to handle near the bottom. Agitate the two liquids to assure they are thoroughly mixed — sulfuric acid is twice as dense as ethanol and the two liquids will tend to form layers. Insert the stopper firmly in order to form an tight seal. Caution: Do not crimp the latex tubing!
Ethene is generated by the following 3-step maneuver as shown in Figure 2.
As each ethene-filled syringe is removed from the apparatus, cap the syringe with a latex syringe cap. After several syringefuls of ethene have been collected, allow the apparatus to cool.
The ethene-filled syringes usually contain 30 - 40% diethyl ether vapors as a by-product of the reaction. Diethyl ether is conveniently removed by "washing" the gaseous products with water in which it is slightly soluble. To do this, suction 10 mL distilled water into the syringe without discharging any gas, cap the syringe and shake the water to dissolve the ether inside the syringe. Remove the cap and discharge the water but not any of the gas. The discharged water will smell like ether. Each syringe should now contain about 35 - 40 mL C2H4(g).
Ethene Generator. Heat has been removed at the time that this
picture was taken in order to control the rate of gas formation. In this photo, 3-mL of ethanol and 3-mL sulfuric acid were used in order to generate multiple syringefuls of ethene. Normally, 1-mL of each liquid is ample to generate two or more syringefuls.
of Ethene. Method II. Thermal Cracking of Polyethylene.
In this method, we will heat polyethylene until it melts and decomposes to smaller molecules including ethene. The apparatus is the same as shown in Figure 1. Obtain 3-g low-density polyethylene from a milk jug, food storage bags, disposable pipet, etc. Be certain that the plastic chosen is indeed polyethylene. Cut the sample into small pieces so they fit into the test tube. (Polyethylene is the 'reagent' shown in Figure 1.) Gently heat the polyethylene until it melts. Continue gentle heating and follow the 3-step procedure described above. Avoid excess heating. If the melted polyethylene becomes too hot, a dense white cloud will form above the liquid surface and the molten polyethylene will darken. If this cloud makes it into the syringe, it will condense to a butter-like liquid inside the syringe.
of Ethene. Method III. Use of a Microwave Oven.
Samples of C2H4(g) also can be prepared conveniently in a microwave oven. (See Generating Gases in a Microwave Oven.)
Unwanted samples of C2H4(g) including the contents of the Waste syringe can be discarded in a fume hood or out of doors. While ethene has a low toxicity, its odor is unpleasant so discharging the gas into the room is not recommended. Method I Wastes: The liquid remaining in the test tube is partially hydrated H2SO4 which can be dissolved by adding about 10-mL water to the test tube and discarded as acidic wastes. Method II Wastes: Allow the polyethylene to solidify. Dispose of the test tube in the trash.
Experiment 1. Reaction
C2H4(g) + Br2(aq) +H2O(l) CH2BrCH2OH(aq) + HBr(aq)
Add 5 ? 10 drops of universal
indicator to the solution. The pH of the reaction mixture decreases
by over two pH. The reaction can be slow and is catalyzed by the
Experiment 2. Reaction
2 KMnO4 + 3 C2H4(g) + 4 H2O(l) 2 MnO2(s) + 3 CH2OHCH2OH(aq) + 2 KOH(aq)
is a mineral (pyrolusite) commonly found in nature and is an important
ore of manganese. Ethylene glycol is poisonous and has a sweet flavor
that dogs like. (For that reason, safer antifreezes, such as propylene
glycol, are now available.) Disposal of syringe contents (MnO2
and ethylene glycol) down the drain with plenty of water is recommended.
Discoloration of the syringe can be removed with 1 M HCl(aq).
Experiment 3. Flammability
Initially ethene burns with a flame from mouth of test tube.
After a few seconds, the flame moves into the test tube where there is still fuel. Note the blue 'ring of fire' inside the test tube.
Experiment 4. Flammability
of Ethene II.
This experiment must be performed in a fume hood. Remove the two syringes and two pieces of latex tubing from the ethene-generating apparatus shown in Figure 1. With a small flame, heat the mixture until the generation of ethene is robust. Allow the gas to be generated for 30 seconds in order to purge the test tube of air. Ignite the gases issuing from the glass tubes. Continue to heat the ethanol/acid. The size of the flame is in proportion to the rate of ethene/ether generation. Blow out the two flame jets and allow the generator to cool.
Experiment 5. Ethene Rockets:
Explosive Mixtures of Ethene with Air and Oxygen.
C2H4(g) + O2(g) 2 CO2(g) + 2 H2O(g)
Experiment 6. Solubility
of Ethene in Alcohol and Henry's Law.
ethanol into the syringe containing 30-mL ethene. Cap the syringe
and push the plunger inward. The ethene will slowly dissolve into
the alcohol. In order to get all of the ethene to dissolve, the plunger
must be pushed inward with considerable force. Once dissolved, the
plunger can be pulled outward and the solution will de-gas — ethene will
be released in a profusion of bubbles. The process can be repeated.
Experiments 7 and 8. Reactions
Experiment 7. Formation
1,2-Dichloroethane is a solvent used to dissolve fats, oils, greases, gums, and even rubber. Equip both the Cl2-filled syringe and the C2H4-filled syringe with separate pieces of latex tubing. Position both tubes into the bottom of the test tube. Simultaneously discharge both gases into the test tube. This provides for maximum mixing of the two gases. Equip the top of the test tube with the balloon. Clamp the test tube in a vertical position with balloon up. Within a few minutes the balloon will begin to inflate inside the test tube (you may need to guide the balloon into the test tube with a blunt object such as a stirring rod). Within the first few seconds of the reaction you should notice the formation of a cloudy aerosol due to C2H4Cl2. This aerosol condenses to a few drops of liquid on the sides and bottom of the test tube. The reaction is:
C2H4(g) + Cl2(g) C2H4Cl2(l)
Next, remove the balloon and lay the test tube on its side in a fume hood for a few minutes. This allows any unreacted chlorine to dissipate. Waft your hand past the mouth of the test tube and towards your nose. Dichloroethane has a characteristic sweet smell. (Alternatively, if you leave the balloon in place overnight, it will 'inflate' inside with test tube with impressive results. The rubber will be tight against the glass and most of the way to the bottom of the test tube.)
Shortly after ethene and chlorine were mixed in test tube and capped with balloon.
Experiment 8. Formation
Equip both the Cl2-filled syringe and the C2H4-filled syringe with separate pieces of latex tubing. Position both tubes into the bottom of the test tube. Simultaneously discharge both gases into the test tube. Without delay, ignite the magnesium ribbon with the burner and hold it inside the test tube. It will initiate a quite different reaction between ethene and chlorine, this one producing soot and HCl:
C2H4(g) + 2 Cl2(g) 4 HCl(g) + 2 C(s)
Various amounts of soot will
be produced. Add water to the test tube and test the pH using Universal
indicator solution. Finally, test for chloride with Ag+(aq).
Experiment 9. Going Bananas
|Two identical green bananas and two identical green pears were allowed to ripen overnight. The left-sided banana and pear were placed in plastic bags containing some ethene and the banana and pear on the right were placed in plastic bags filled with air. By the next day, the treated banana was 'black' and the treated pear was very soft.|
Experiments 10 and 11.
Catalysis Reactions Involving Ethene.
These two experiments require the Gas Reaction Catalyst Tube which is sold by Educational Innovations has specifically designed a for these microscale gas chemistry experiments.1 The catalyst is housed in a glass tube. The assembled apparatus is shown in Figure 3.
syringe on the left contains the reagent gas mixture ready to be passed
though the catalyst. A 2-cm length of latex tubing connects the syringe
to the tubing. To the right of the catalyst tube is the receiver
syringe, also connected by latex tubing. The plunger of the receiver
syringe must be able to move freely in the syringe barrel. This is
assured by lubricating the black rubber plunger diaphragm. Two ring
stands and clamps, not shown, hold the two syringes in the appropriate
position above the burner's flame. The clamps should not hold the
syringes too tightly, and should allow for free rotation of the syringes
and catalyst tube for even heating.
Figure 3. Gas Reaction Catalyst Tube
Gas Reaction Catalyst Tube, available from
Educational Innovations, shown attached to two syringes.
Experiment 10. Catalytic
Oxidation of Ethene.
Fill the reagent syringe with 50 mL air (0.43 mmol O2) and 10 mL ethene (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 3. Pass about 10 mL of gas mixture through the catalyst tube to (a) check for leaks, (b) determine that the plunger in the receiver flask moves freely; and (c) 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.) Heat the catalyst tube evenly on all sides for a total of about 30 seconds. (CAUTION: Heat from a Bunsen burner flame is capable of softening the glass portion 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 only a cool Bunsen burner flame. 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 this should happen, remove the flame and adjust the flame.)
Slowly pass about half of the C2H4/air reagent gas mixture through the catalyst tube over the course of about 30 seconds. Be alert for problems — the volume of gases collected in the receiver syringe should almost equal the volume decrease in the reagent 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. Air is only 21% O2 and the reaction stoichiometry requires 3 volumes of O2 for every volume of C2H4:
C2H4(g) + 3 O2(g) 2 H2O(g) + 2 CO2(g)
Test the product gases collected
with lime water: Add 5 mL lime water to a medium sized test tube.
Discharge 10 - 20 mL the gas collected above the surface of the lime water.
Periodically stopper the test tube and shake the mixture. A cloud
of CaCO3(s) will confirm the presence of CO2(g).
Experiment 11. Catalytic
Hydrogenation of Ethene.
Fill the reagent syringe with 30 mL ethene (1.2 mmol) and 30 mL hydrogen (1.2 mmol.) Connect the reagent and receiver syringes to the catalyst tube as shown in Figure 3. Heat the catalyst tube while pass about 10 mL of gas mixture through the catalyst tube to purge it of air. Remove the receiver, discharge the air and then reconnect 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/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 gaseous reactants become 1 mol of gaseous products if the reaction efficiency is 100%. In our experience, these experimental conditions cause hydrogenation with about 50% efficiency.) 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. The reaction is:
C2H4(g) + H2(g) C2H6(g) DH = -137 kJ
The hydrogenation under these conditions is not 100% efficient. In order to test that hydrogenation has occurred, simultaneously react 10-mL of the unreacted mixture and 10-mL of the product gases with separate bromine water solutions (2.0-mL Br2(aq) aliquots in medium test tubes). Stopper and shake the mixtures. The unreacted gas mixture contains more ethene and will react with more Br2(aq) producing a colorless solution. The product gas mixture contains less ethene and may not react with all of the Br2(aq) present — and will stay red. If both solutions turn colorless, add 1.0-mL more of Br2(aq) to each test tube.
chromatography can also be used to analyze the reaction mixture. (Column:
Porapak N 80/100, 6-ft (180 cm), inside diameter = 0.085 inches (2.2 mm);
helium flow: 30-mL/minute; room temperature; Alltech Part Number 2716;
telephone: 847-948-8600) Typical results are given in Figure 6. Note
that the ethane peak is larger than the (unreacted) ethene peak indicating
that over 50% conversion has taken place.
Figure 6. Gas Chromatogram of the Product Gases from the Hydrogenation of Ethene.
At the end of the experiments, wipe excess lubricant off of rubber diaphragm.
Clean all syringe parts (including the diaphragm), 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
|This article first appeared
in Chem13 News in September, 1999. The authors of the original
Chem13 article are:
From the Department of Chemistry, Creighton University, Omaha, Nebraska 68178 USA:
Also from Creighton University:
Viktor Obendrauf, Bundesoberstufenrealgymnasium Feldbach, Austria
*RC gratefully acknowledges financial support from the Betty A. and Donald J. Baumann Family Scholarship
St. Albert's Day November,
from left: Rebecca Catahan (senior), Bruce Mattson (PI), Paras Khandhar (junior)
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(This page last updated 29 January 2002)