Microscale Gas Chemistry
Experiments with Ethene

Link to C2H4 data page including physical properties.

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.
    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.

Suitability.
    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.

Syringe Lubrication.
    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.)

Chemicals.
  • 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.

    Figure 2.  Three step procedure for generating ethene.

        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.





    Preparation 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.
     

    Preparation 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.)

     Disposal.
        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.
     
     


    Experiments with Ethene.

    Experiment 1. Reaction with Bromine.
    Equipment:

    Chemicals:     Use of a fume hood is recommended when working with bromine water.  Connect the latex tubing to a glass disposable pipet that will be used to bubble ethene through the bromine water solution.  Connect the other end of the latex tubing to an ethene-filled syringe.  Add 10-mL bromine water to the test tube.  Slowly discharge the ethene just above the surface of the bromine water. Stopper the test tube and shake. The reaction between aqueous bromine and ethane is:
     
     

    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 glass surface.
     
     

    Experiment 2. Reaction with KMnO4.
    Equipment:

    Chemicals:          Prepare a solution of KMnO4 by dissolving 0.25 g pulverized KMnO4 in 30-mL water.  Stir thoroughly because KMnO4 dissolves slowly.  The solution contains 1.6 mmol KMnO4 and is intensely deep purple.  Suction the KMnO4 into the syringe containing the ethene.  Cap the syringe and shake the syringe to mix reagents.  The volume of gaseous ethene will decrease as the reaction proceeds.  The reaction produces water-soluble ethanediol, commonly called ethylene glycol and sold as anti-freeze.  Permanganate is converted into insoluble brown MnO2.

    2 KMnO4 + 3 C2H4(g) + 4 H2O(l)  2 MnO2(s) + 3 CH2OHCH2OH(aq) + 2 KOH(aq)

        MnO2 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 of Ethene.
    Equipment:

    Chemicals:     Use water displacement to fill a large test tube (22 x 200 mm) with ethene from the syringe.  Stopper the test tube underwater.  Remove the test tube from the water and position with the open end up.  (You may hold the test tube with your hand, but avoid the top half which will become hot.) Darken the room and ignite the gas with a burning candle.  Ethene will burn down the test tube with an attractive blue flame that sometimes looks like a descending ring of fire.  Tilt the test tube back and forth.  This allows air to enter and the blue ring can be made to move up and down the test tube.  Unlike ethyne, ethene does not form soot as it burns.  After the flame goes out, inspect the test tube.  It will be hot to the touch.  Test the contents of the test tube for CO2(g) by adding 10-mL lime water to the test tube and shaking the contents.
     

    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.
    Equipment:

    Chemicals: Method I.
        Replace the syringe cap with a short length of latex tubing inserted into a disposable glass pipet.  Ignite a small candle.  Direct the pipet in the vicinity of the burning candle and slowly discharge ethene.  A yellow flame will burn from the pipet due to the sodium in the glass.  By quickly discharging the burning ethene, a 20-cm narrow flame will be produced!

    Method 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.
    Equipment:

    Chemicals:     Prepare several Beral pipet 'rockets' by removing all but 2-cm of the stem from several extra-large polyethylene (disposable) pipets.  Fill the pipet rockets completely with water and store them open-end down in test tubes filled with water.  Remove the cap from the syringe and slip the water-filled pipet rocket over the LuerLOK fitting.  Bubble the C2H4(g) into the rocket until it is half-filled.  Fill the rest of the pipet with O2(g), leaving some water in the stem.  Store rockets in the water-filled test tube until ready for use.  (See: General information on successfully filling and launching rockets.)
        Position the rocket over the wire leads of the sparker.  Water must remain in the stem because this serves as the propellant; however, the ends of the wire leads must be above the water in the gas-filled region of the rocket.  If the water leaks out of the stem while positioning the rocket over the wires, immediately fill the stem again by holding the wires plus rocket assembly in a cup of water and suctioning a very small amount of water into the stem.  Trigger the sparker and the rocket will fly 5 m or more.  A fireball is noticed in a darkened room as the gas mixture ignites.  The reaction is:

    C2H4(g) + O2(g)  2 CO2(g) + 2 H2O(g)







    Experiment 6. Solubility of Ethene in Alcohol and Henry's Law.
    Equipment:

    Chemicals:     Ethene is marginally soluble in water; one volume of C2H4 dissolves in nine volumes of water at 25 oC.  In alcohol, however, two volumes of C2H4 dissolve in one volume of alcohol.  In this experiment, we will dissolve an equal volume of ethene in ethanol.

        Draw 30-mL 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 with Chlorine.
    Equipment:

    Chemicals:     For each part of this experiment you will need 60-mL ethene in a single syringe. To do obtain this, combine ethene from two syringes by transferring the gas through a 2-cm length of latex tubing.

    Experiment 7.  Formation of 1,2-dichloroethane.
        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 of Soot.
        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 with Ethene!
    Equipment:

    Chemicals:     Ethene is used to ripen bananas and citrus fruits.  Many fruits emit ethene as they ripen naturally.  You will need gallon-sized sealable plastic bags, two pieces of each sort of fruit to be ripened and 30-mL ethene for each type of fruit.  Place each piece of fruit in a separate sealable bag and seal shut with plenty of air inside.  One piece of each fruit will serve as the control.  To the other bag, add 30-mL ethene by simply discharging the gas into the bag and resealing the bag.  Check the bags over the next hours and days.
     
     
    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.
    Equipment:

    Chemicals:


         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.

         The 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.

         Gas 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.


    Clean-up and Storage.

       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 barrel.



     
     
    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:

    • Bruce Mattson, faculty member, principal investigator
    • Martin Hulce, faculty member, co-principal investigator
    • Michael Anderson, faculty member, co-principal investigator
    • Jiro Fujita, professional staff member
    • Rebecca Catahan,* undergraduate chemistry major,  graduated May, 2000, currently in PhD program in chemistry at University of North Carolina
    • Paras Khandhar, undergraduate chemistry major, will graduate May, 2001, plans to go to medical school
    Also from Creighton University:
    • Maneesh Bansal, undergraduate student, currently a health administration major, will graduate May, 2001, plans to go to medical school
    • Andrew Mattson, undergraduate student, currently an English major with journalism concentration, plans to graduate in December, 2001
    • Anand Rajani, undergraduate student, currently a psychology major, plans to graduate in May, 2001 and go to medical school
    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, 1999

    from left:  Rebecca Catahan (senior), Bruce Mattson (PI), Paras Khandhar (junior)

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    (This page last updated 29 January 2002)