High School SMILE Meeting 1999-00 -- 05-06 Academic Years Combustion Chemistry

12 October 1999: Pat Riley [Lincoln Park HS]

1. Examples of physical and chemical changes are easy to find, but examples of sublimation that are inexpensive are harder to find. One example concerns room air fresheners [important products indeed!-PJ)].
2. Next we worked on balancing equations for chemical reactions.
   1. We first identified certain compounds that are easy to work with.
   2. Then we discussed what happens in combustion of natural gas: [CH₄ methane and 0₂ [air] combine to make CO₂[carbon dioxide] and H₂O [water] . ...the unbalanced reaction equation ...
      CH₄ + 0₂ ---> CO₂ + H₂O
   3. By using the large plastic balance we were able to balance the equation by placing more CH₄ icons or more H₂O icons on the left side, or more CO₂ or H₂0 on the right side, until the arms of the balance evened out. We then took the CH₄ and 0₂ icons from the left side, and put them on the board. Then we took the CO₂ and H₂0 icons out of the right hand side, and placed them on the board.
   4. We then counted how many C's and H's were on the left and right sides of the board, and tried to even them out with the number on the right side, since we must follow the law of conservation of atomic species [no cold nuclear fusion, please!-PJ],
   5. Once we had all atomic species balanced we put the icons back on their respective sides, and the scale balanced. We then placed the number for each compound before its symbol, getting 3 CH₄ + 6 0₂ ---> 3 CO₂ + 6 H₂0
   6. Then we tried the same thing with C₂H₆ [ethane], getting 2 C₂H₆ + 7 0₂ ---> 4 CO₂ + 6 H₂O
   7. The element icons were made of construction paper of the same color and size. Metal washers were placed on the back of the paper to make the weights proportional to the corresponding atomic weights. [mass, actually -PJ]

10 September 2002: Ken Schug
made several phenomenological presentations from his "shoeboxes he uses when teaching the general chemistry course at IIT. We also signed up for date to share phenomenological presentations with our colleagues. (see below)

He held up a gallon size clear kitchen bag and asked for advice on how to fill it with air. When there was agreement that swooshing it was preferable to exhaling into it because exhaled breath has a different composition from air (less oxygen and more carbon dioxide), he swooshed, closed the opening with a twist tie and hung the bag on a clamp on a ring stand. He then took another bag from the same roll, poured in about 30 mL of 3% hydrogen peroxide solution, added a package of dry yeast and applied a twist tie. We observed foam forming, the bag expanding in size, and (by three teachers in the front row) a report that heat was being given off and concluded that a chemical reaction was occurring. Ken pointed out that hydrogen peroxide, H₂O₂, is one of only two compounds containing only hydrogen and oxygen stable under normal conditions (the other, of course, is water) and that, although it contains more stored chemical energy than a mixture of water and oxygen gas, the rate of the reaction to form these products is very slow in the absence of a catalyst. Yeast is one of many chemical or biological substances that can serve as a catalyst for that reaction.

He then lit a cigarette and touched the glowing end against the bag containing air; we observed that the cigarette melted a hole in the bag. When he did applied the cigarette to the other bag, however, the bag burst into flame, which continued for several seconds, consuming about one third of the bag. Ken asked for hypotheses to explain this event and accepted the suggestion that the higher concentration of oxygen was responsible. The higher concentration resulted in a chemical reaction fast enough to keep the fire going. (Ken pointed out that if more hydrogen peroxide had been available for the reaction, the effect would have been much more dramatic.

Ken then held up a flat bottle containing a medicine dropper floating (vertically) near the surface which several teachers recognized as a Cartesian diver. He passed the bottle around and heard several comments that the bottle seemed to made of glass; not plastic. He confirmed the it was indeed a glass bottle and got several predictions that the dropper would not submerge when the bottle was squeezed because you need a plastic bottle for Cartesian divers.. He then gave everyone a chance to test that hypothesis phenomenologically by squeezing the bottle, discovering, amid oohs and aahs, that "it worked!" After an explanation that the "diving" occurs because squeezing the flat sides of the bottle slightly reduces the volume which results in an increase of pressure inside the bottle (which is completely filled with water and is tightly capped.

Since the dropper is partially filled with air (the liquid-gas interface was just visible below the bulb) the increased pressure forces more liquid into the dropper as the volume of air decreases slightly (Boyles' Law in action!), which makes it heavier, so it sinks. [Submarines use the same principle] Instead of taking a bow, Ken said, "wait a minute, I'm not finished" and, with the aide of an assistant, extended the experiment. As the assistant pushed steadily on the front and back flat sides of the bottle to keep the diver submerged, Ken pushed on other two sides (perpendicular to the aide). We observed the diver return to the top of the battle, We decided that pushing on the edges cause a slight outward bulge of the flat sides, resulting in an increase in the internal volume, expansion of the gas in the diver (making it lighter) and causing it to rise to the surface.

Ken then opened another shoebox, took out a jar of all purpose flour and poured some on the top surface of an inverted (empty) tuna can, saying He was going to see if flour could be used as a renewable source of energy. When he held a match against the flour, there was a little charring but not a sustained flame, a necessary requirement for a successful energy-producing combustion. He then poured some flour into a plastic funnel with a long piece of rubber tubing attached to the exit, turned out the light, struck a match and led it above the funnel as he blew forcefully into the tubing. When the flour cloud reached the burning match we saw a ball of flame shooting up toward the ceiling.

After some discussion, we concluded that the difference in behavior of the flour in the two parts of the experiment was due to the fact that as a "cloud" each particle of flour has many oxygen molecules from the air surrounding it but in a pile most of the space around each flour particle is occupied by other flour particles so the reaction is slower and does not proceed fast enough to keep the combustion going,

In retrospect, the first and third experiments demonstrate the four major factors that can affect the rate of a chemical reaction:

• concentration of a reactant,
• presence of a catalyst
• increased temperature
• a larger surface area of a reactant (for solids and liquids)

04 November 2003: Lilla Green [Hartigan School, retired]       Energy
After recounting her 35 year career at Hartigan School which included 10 years running a multi-grade "lab" (sounds phenomenological!), Lilla  led us through a broad-ranging activity on ENERGY. She first asked for words related to energy which she wrote on the board; our list included: food, heat, electricity, sound, potential, kinetic, and others (think we missed nuclear). She then struck a match and lit a candle while we called out related energy terms, heat, light, friction, sound, chemical; then pulled a variety of toys out of her "energy bag" and asked individuals to supply related words. Toys included a Slinky, wind up action toys, remote controlled car which Ben got working by actually reading the directions, a last resort for many of us when dealing with life's little problems. Small groups of us then examined one of three sets of five pictures and attempted to arrange them in a logical chronological order (ball rolling down a hill and striking a stationary object, candle being lit with a match, a tree growing under a sun), then described the different types of energy represented.

Ken Schug asked "Since we are told that energy is conserved where did the energy go?" and got several answers that it is changed from one form to another, though often not easily detected; e.g. if we drop a rock on the ground the loss in potential energy of the rock is transferred to the (kinetic) molecular motion at the site of impact (resulting in a very small increase in temperature). Because the car ran on batteries, Ben suggested that Ken provide an explanation of how batteries work. His non-phenomenological explanation was that a battery (really cell) is a way of tricking two chemical reactants to send electrons being transferred between them through an external circuit, where it can do useful things as an electric current, rather than directly where only heat is produced. [Ken promised to do phenomenological presentation next time if somebody reminds him!] Great way to share your years of teaching with us beginners Lil!!

10 February 2004: Ron Tuinstra [Illiana Christian High School, Chemistry]        The Concept of the Mole
Ron  brought in a roughly square piece of galvanized iron (iron with a zinc coating) about 2.5 cm on a side and 1 mm thick.  He weighed and measured the piece, and then removed the zinc from it by soaking it in hydrochloric acid: Zn + 2 HCl ® ZnCl₂ + H₂ (bubbles)   After the chemical reaction had ceased, he thoroughly washed the piece in water, and then dried it.  The metallic piece was visibly thinner than it had been.. Our objective was to determine the approximate number of zinc atoms on the piece of galvanized iron, and the approximate thickness -- in atoms -- of the zinc coating.  The procedure involves measuring the mass and size of the galvanized iron, before and after the zinc coating is removed.  From the masses of zinc and iron, we can calculate the number of moles and atoms of each metal.  By using the known radius of the zinc atom and assuming that the atoms of zinc are stacked directly on top of each other in the coating, we can estimate the thickness of the coating.

We took data and made calculations concerning the piece of galvanized iron, as given in this table:

10 February 2004: Chris Etapa  [Gunsaulas Academy]         Energy Ball!
Chris brought in an Energy Ball [http://www.stevespanglerscience.com/product/1406], which she uses for teaching about electrical circuits.  The Energy Ball resembles a ping-ping ball, with two metallic contacts on its surface, as well as a battery, a  light bulb, and a "beeper"  hidden inside.  When the contacts are connected,  the light goes on  and the beeper sounds, signaling that a circuit has been completed!  When one of us put our thumb on one of the contacts and our forefinger on the other one, the light and sound again were produced.  Next one person touched one contact and another person touched the other contact.  Nothing happened -- until the two people touched their hands together -- again! -- light and sound!. We then formed a "human chain" with several people holding hands When the two people at the ends of the chain each touched the contacts as before -- sound and light!  When the human chain was broken, the signal stopped abruptly.  Remarkable, but how come?  Pat Riley and Ben Stark pointed out that there is saltwater on our skins, and electrolyte solutions throughout our bodies, which are fairly good conductors of electricity.  A small amount of electricity is conducted by our bodies, completing the circuit and triggering the sound and light from the ball.  These human circuits are similar, in principle, to circuits involving metallic wires.

Fascinating stuff, Chris!

24 February 2004: Bradley Wright [Eisenhower HS Blue Island, Chemistry]         Fuel Cell Football ©
Brad recently attended a workshop sponsored by Flinn Scientific Foundation.   One of the exercises, called Fuel Cell Football ©, used combustion of a small volume of a hydrogen-oxygen mixture to propel a plastic projectile across the room --- about 4 meters --- and through the goal posts --- a "chemical field goal"!

Note:  Rocket launch experiments such as this one should be done only under the supervision of an experienced expert!

The device is prepared using the following reactions:
• Zinc metal reacts with hydrochloric acid to produce hydrogen gas: Zn + 2 H Cl ® Zn Cl₂ + H₂.
• Yeast is used to catalyze the production of oxygen from hydrogen peroxide: 2 H₂O₂ ® 2H₂O + O₂
• The rocket (small plastic vial) is filled with a mixture of H₂ and O₂ , which we then placed over the end of a piezoelectric igniter.  The spark from the igniter provides activation for reaction 2H₂ + O₂ ® 2H₂O, which launches the vial (most of the time!) through a scale model of goal posts.

Proprietary details for constructing and launching this projectile may be obtained from Flinn Scientific Foundation [http://www.flinnsci.com/].

Great phenomenological chemistry, Brad! Excellent!

28 September 2004: Ken Schug [IIT Chemistry]     Ken's "Chemistry Road Show"

• First, Ken showed two 10 oz (300 ml) pop bottles that were  both about 2/3  filled with a reddish liquid. They looked the same, but were they? How could we decide this? Density? pH? Smell? Open the bottles and mix them together was Ken's idea. When we mixed them, they appeared to be the same, as there was no separation of the two into different layers, etc. Ken confirmed that they were the same, a solution of CoCl₂. The color comes from the Co²⁺ ion.

  We investigated further. One bottle was warmed (in a warm water bath) and the other was chilled (in an ice bath).  The chilled one became redder, but the warmed bottle turned blue! Co²⁺ ions hydrated with 6 waters (pink) and (CoCl₄)^2- (blue) were in equilibrium with each other, and this equilibrium point was shifted by the temperature. The different colors of the two species are due to the different electron energy levels between the two.  A  Co²⁺ ion in "cobalt glass" that is structured similarly to the (CoCl₄)^2-  gives cobalt glass its distinctive blue color.
  

• Ken suggested that flour could be a renewable fuel! He poured out some flour (the flour had been pre-dried in an oven) into a metal dish and tried to light it with a match (without success). He then poured out some flour into a small plastic funnel attached to about 2 feet of rubber tubing. With the lights out, Ken blew gently on the tubing to make an aerosol of the flour above the funnel while he put a lighted match in. We got a great flame! The greater oxygen to flour ratio of the aerosol allowed the flour to burn.  This is the same principle that sometimes leads to grain elevator explosions!
  
• Into one baggie (sealable with a tie) Ken put hydrogen peroxide solution and dry yeast. Peroxidase in the yeast converts the peroxide into water and oxygen; the oxygen collects in the baggie when it is tied off. We could see the results of the reaction as a foaming (the reaction gave off heat as well, and Ken could feel the baggie get warmer). A baggie just filled with air was pierced with a lighted cigarette, but nothing happened. The yeast-peroxide baggie pierced the same way resulted in a bright glow when the cigarette pierced the baggie; this was due to the greater concentration of oxygen inside this baggie than in ordinary air, which supported a greater amount of combustion. 

08 February 2005: Pat Riley [Lincoln Park HS, chemisty]       Conservation of Matter
Pat brought in some portable, top-loading digital balances. Each group had three small, stoppered bottles labeled A, B, and C. A and B each contained a few grams or so of a white powder, and bottle C was empty.  First weigh each bottle with stopper. (Note: it is important to keep the cork stoppers with their respective bottles, because of the variation in mass among stoppers.)  Then pour the contents of bottles A and B into bottle C, replace the stoppers, and reweigh all three bottles. Then continue by shaking bottle C . We saw the white powder change to a creamy color. Then the bottle got cold, and there was an ammonia smell  that was detectable despite the stopper. A contained Ba(OH)₂, and B contained NH₄Cl, which reacted to make ammonia (NH₃), Barium Chloride (BaCl₂), and water (H₂0). We reweighed the bottle C (at least before a great deal of the ammonia had escaped through the cork). Its mass was more or less unchanged from when A and B were added together.  The comparison of total masses demonstrates (within experimental error) that everything we put in bottle C remained there.  This occurred even though the various atoms were rearranged in the chemical reaction that occurred. ... Eventually, of course, most of the ammonia would escape, decreasing the total mass of bottle C. 

Great!!

01 November 2005: Walter Kondratko (Steinmetz HS, chemistry)      Lemon Batteries and Burning Pennies
Walter had taken lemons and placed two electrodes (one Zinc and one Copper) into each lemon. The Zn-Cu pair has a difference of standard reduction potential of 1.1 Volt. A Voltmeter held across the two electrodes will test this, as the acids in the lemon will drive an oxidation-reduction of the couple where they are inside the lemon. By putting such "lemon cells" in parallel and series they can investigate various properties/phenomena pertaining to electrical circuits.

Walter also scratched a penny (minted after 1982, with a Zinc center). He then held the penny in the flame of a portable torch to melt the Zinc so that it would flow out of the scratch. This works because the melting point for Zinc is much lower than that for the Copper "veneer" on the outside of the penny.

Then Walter heated pre-1982 penny and suspended it from a rod. He heated the penny to red hot and then suspended it over a bit of acetone in a beaker. The heat from the penny caused oxidation of the acetone vapor, which produces ketone and methane. The methane burned near the hot metal and this combustion could be seen as a glow around the penny. In other words the glow on the penny persisted as long as the penny was still hot enough to oxidize the acetone vapor and to ignite the methane. Walter made an even better glowing apparatus using a copper strip of about 2 by 10 cm.  For additional details see the Purdue University webpage on Catalytic Oxidation Demonstration: http://chemed.chem.purdue.edu/demos/moviesheets/19.5.html.

Terrific! Thanks, Walter.

04 April 2006: Walter O. MacDonald (VA Hospital and CPS)                The EnergyCel
Walter brought a video describing the Energy Cel:  http://www.myenergycel.com/. It claims to increase the efficiency of internal combustion engines when placed around the fuel line. The theory is that the magnetic field produced by the magnets in the device breaks up clusters of fuel molecules, resulting in more complete combustion. One dynanometer test overseen by a news team showed a 10 % increase in gas mileage and a road test (overseen by the same news team) showed a 27 % increase in gas mileage. The cost of  the device plus installation is about  $300. Despite the reported results our group was skeptical! Walter, however, put one on his car and his anecdotal report is that his car seemed to run better (although he did not calculate fuel efficiency before and after). Porter also pointed out that if the EnergyCel results in a leaner mix of gas to air, it might cause too hot a temperature in the cylinder, which might result in burned valves. A spirited discussion of modern internal combustion engines, modern gasoline, etc. ensued!  Let us know how your gas mileage goes!  Thanks, Walter.

18 April 2006: Carl Martikean (Proviso Science Academy)                        Alternative Fuels
Carl passed out copies of a Fuel Comparison Chart, which he obtained from the Department of Energy website:  http://www.eere.energy.gov/afdc/pdfs/afv_info.pdf.  Carl pointed out that E-85 (85 % ethanol-15 % gasoline) produces only  80,000 BTU of energy per gallon, as opposed to 109,000-125,000 BTU per gallon for gasoline. Despite this, tests have apparently shown that cars run on E-85 get  about 90% of the mileage obtained with gasoline. How can this be? It was suggested that E-85, a partially oxidized fuel, should behave more like (more completely hydrogenated) bio-diesel material --  and similar to the non-oxidized hydrocarbons in gasoline. It might then have nearly the same amount of energy per gallon as gasoline. However, the issue was unclear to us.  Does anybody know?
An interesting and provocative question.  Thanks, Carl.