edited by
tested demonstrcitions
GEORGE L. GILBERT Denison Univerrity Granville, OH 43023
Entertaining Chemistry John F. Elsworth University of Cape Town, Rondebosch, South Africa 7700
Part 1. A Volcanic Serpent Checked bv:
George ~ o l l a s t o n Car on U n vcrsty Caron. PA 16214 Have you ever watched a n egg hatch into a chicken? Here is a n opportunity to demonstrate the emergence of a snake from an "egg" in a n amusing way to a n audience of any size. This demonstration also illustrates the necessity of heat to induce the hatching process! I t combines both the well-known "volcano" and the "Pharaoh's serpent" reactions (I,2). Materials To Produce the Egg ammonium dichromate (ca.30 g) mercury(I1)thiocyanate (10 g) dextrin (1.0 g) distilled water (about4 drops) To Perform the Demonstration
Demonstration In the demonstration itself, the "egg" is laid on the asbestos sheet and covered with a pile of ammonium dichromate. This is "the nest"! To start the reaction, a small depression is made on top of the pile into which a spatula tip heaped with the powdered potassium permanganate is added followed by a few drops of glycerine. The ignition time can be shortened by warming the glycerine a little beforehand. The permanganate ignites after 10 to 30 s, depending upon the temperature. At this point the lights may be switched off to render the appearance of the resulting "volcano" more dramatic. As this dies down, the lights are switched on. After a brief period, a one-meter long serpent will crawl out of the mound of "ash". This spectacle will take about a minute to complete. Equations The "volcano" reaction is a thermal decomposition of ammonium dichromate ( I ) to form a pile of chromium(II1) oxide:
+ Cr207(s)+ N2(g)+ H20 (NH4)2Cr207(s)
(1)
The delayed combustion of glycerine by permanganate to start the volcano is reported (2) to proceed according to the following equation:
The "Egg"
powdered potassium permanganate (ca. 1g) glycerine (a few drops) asbestos sheet (or other fire-resistant sheet) Caution M e r c u r y compounds are toxic. Wear gloves when preparing the "egg". Wash the hands well after the preparation. The chemistry teacher should perform this demonstration i n a well-ventilated room because some smoke is produced. The writer usually performs this demonstration at the end of a chemistry lesson or show in order to minimize audience exposure to the fumes. Do not allow observers to handle the "serpent" hecause of its toxic nature. Wash hands thoroughly after the experiment.
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The writer did not locate information in the literature on the structure of the "serpent". I t appears to be carbonaceous. I t is highly likely, however, that a mercury sulfide complex contributes to the structure. General This entertaining reaction demonstrates spontaneous delayed combustion and exothermic reactions, and it is a good analogy for crystal growth. Literature Cited I. &*a. H.N.:Dutton. F. B. nsid Demonstmlions in Chemistry, 6th ad.: 1969, pp 5 and 29. 2. Humphrey~.D. Demonsfmfion Chemistry 1983.33.
Part 2. A Homemade Hydrogen Rocket Procedure Prepare the "egg" a few days before the demonstration. Thoroughly mix together the mercury(I1) thiocyanate and dextrin in a crucible. Add distilled water carefully dropwise while mixing with a spatula. Four to six drops of water usually are sufficient. Too much water produces a runny paste. Roll the mixture between gloved hands to form a round ball. Allow the ball to dry out. Leave it on top of a drying oven for a day or two. 1128
Journal of Chemical Education
Checked by: George Wollaston Car on U n verslly Caron. PA16214 Afavorite demonstration a t anv chemistrv lecture is the "pop" produced when a mixture of hydrogen and oxygen in a 2:lvolume ratio in a 350-mL bottle is e x ~ o s e dto a candle (or other) flame (1,2). Here is an opportunity to extend this
reaction by making a hottle lift-off! Moreover the reaction can be done easily a t home, providing certain precautions are taken. Materials About 30 to 40 g of aluminum will be needed. Aluminum foil and other sources of aluminum of suitable quality are some "pie" dishes, milk bottle tops, and aluminum wrappings from foods. (Avoid using aluminum beer or cold drink cans because they have protective coatings that make them impervious to attack by sodium hydroxide). A tablespoonful of sodium hydroxide is the only &her reagent required. Caution: Caustic soda available commercially must be handled with great care! A "auart-sized" heer bottle is used to generate the hvdrogen, and a plast~cbucker with ca. 10 ern water 1s necessan Ibr cooiine the reaction. A2-L oolvthene "coke" bottle and " a large empty coffee can are used for the "rocket" and its launching pad. Finally, have a pair of safety glasses or other form of eye protection a t hand. Following a modification of the Battino orocedure (2).the outside cover of the base of the coke bottle is first removed and, using a sharp knife. a hole of ca. 5-cm diameter is cut in the bottom. The original plastic cap must be replaced with a metal one. Many 'soft drink" bottles have metal caps that are suitable. Make a small hole in the center of the cap with a 2mm diameter nail. With a large screwdriver (or other device), punch some wide holes in the base of the coffee can so that air may enter readily. The rocket and its launching pad are now ready for count-down.
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Procedure Tear or break the aluminum foil into pieces which can be nushed throush the neck of the heer hottle. Carefullv oour In the sodiukhydroxide flakes, add a half cupful o g a t e r (ca. 100 mL) and sentlv swirl the mixture in a horizontal plane. immerse tLe bottle in the water in the hucket to minimize overheating. After one to two minutes, the reactlon bcg~nswith a r a p ~ dnse in temperature and thc evolution ot'hvdroeen. Thr nrck of the generating bottle is then inserted"intoUthe hole in the base-of the "rocket" to allow entry of the hydrogen. Close the aperture in the lid of the rocket to prevent escape of the gas, with a piece of masking tape. After about a half minute, all the air should have been displaced. The rocket, with the top aperture closed, is transferred vertically into the launching can, which has been placed on a brick, or some other support to allow free access of air through the punched holes. Open the small aperture and immediately apply a flame to the issuing gas. Stand clear! The time for "lift-off' depends upon the size of the aperture ( I ) .Try to catch the rocket as it falls! Precautions The chemistry teacher, in fact, should first demonstrate this experiment a s a scientific exercise. The science teacher should point out the hazards of the experiment steo hv steo. Students should be warned of the ootential da&e;s when working with hydrogen with special stress on the explosive properties of hydrogenlair mixtures. (Refer to the Hindenburg disaster.) One should stand clear when igniting the hydrogen a t the top of the bottle. Eye protwtion is essential. Wear safety glasses. Never look lnro n rencrmn bortl~r u st c. ~fsornrthlng;1. happemng That's when things do happen! Caustic soda must he handled with great care. If any is spilled on the hands o r any part of the body, wash immediately with plenty of water.
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Cooling of the reaction bottle is essential because the reaction is exothermic. It may be necessary to add even more water into the cooling hucket. Thoroughly rinse the hottle with water and destroy the bottle, at the conclusion of the experiment. The bottle should not he used as a drinking receptacle.
Equations 2AI(s)+ 2NaOH(aq)+ 6H20+ 2NaAl(OH),(aq)+ 3H2(g) (1) or, iouically, 2A1(4 + 20H- + 6H20+ 2AI(OH),-(aq) + 3H2(g) followed by: 2H2 + O2+ 2H20
(2)
Notes The reason for the delay in lift-off has been studied and reported in a n unpublished paper ( 2 ) .As the hydrogen burns, air enters via the bottom of the rocket. Only when the composition of the mixture falls to below 74% hydrogen (vIv)(3)will ignition occur. This experiment is more suitable than the 'jumping can" using "coal gas" a s a better "lift-off' results. I n a laboratory, it is simpler to use "hottled" hydrogen. Coal gas (methane) also can he used, hut there is a longer time delay before lift-off. "LPG" gases such a s propane and butane are unsuitable because being denser than air, they tend to drain out a t the bottom of the bottle. One can adapt the procedure easily to fill balloons. Choose a balloon that will fit across the mouth of the hydrogen-generating hottle. Here, however, it is essential to keep the reaction reasonably cool to avoid caustic soda entering the halloon via the vapor. Remove the balloon when filled. and tie with stringin the usual wav. I t is imoortant to note that these balloons should be usedbut-of-dohrs only because they contain hydrogen. Morcovcr, kecp all flames away. Agood exercise is to calculate the number of 2-L size balloons that can be filled using 27 g ( i.e., l mole) of aluminum, based upon the above equation. Assume a temperature of 20 "C and a pressure in the balloon of ca. 2 atm. Literature Cited 1. &a. H. N.; Dutton, F B. TPsfPdD~monstrolions in Ch~mlslry.6th ad., 1969,p 59. 2. Battino. R.;Bsttino. B. S.; Li, Y.:Llsguno, C. DdqvrdErpiosions, personal communication. 3. Handbook ofChemistry andPhysics, 51st ed,; Chemical Rubber Co., p 0-82.
Johnny's Saga in Chemistry Checked by:
David Speckhard Loras College Dubuque, IA 52001 The following poem was the winner among many entries in a competition many years ago,' and it adds entertainment to a lighthearted chemical show or even to a class of students who have completed a course of study on acids and bases. While reciting the poem, the writer performs the appropriate reaction from those listed helow. Johnny finding life a bore, drank some H2S0, (a). Johnny's father, an MD, gave him CaC03 (h). Now he's neutralized, 'tis true, hut he's full of C02. From the gas to free the lad, what a brainwave father had. He just told his son, with glee, "Go and breathe some NH3. C02and NH3 come to sol uolatile." -
'Tne wr ler s mab c lo trace tne autnor of me poem b ~ oe t .eves !hat tne compel l on was organ zea by Chemnsrty and indusrty (Bnrain) in the early 1950's. Volume 72 Number 12 December 1995
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Johnny, who'd no school certif. took a much too hefty sniff. He took more than was his due (c). Soon he turned red litmus blue! Johnny, basic to the care, drank more HzSO4(dl. Father gave him chalk galore (el. Now he's where he was before! Where t h e audience understands chemical equations, I show these on a n overhead projector. The equations for t h e different steps follow. H2S04+ CaCO, + CaS04 + H20 + C02(g) (1) C02 + NH, H2S04+ NH,
+ H20 + NH4HC0,
(2)
+ NH4HC0, + (NH4),S04 + C02 + H20 (3)
Repeat e q 1.
Materials Required A tall, wide gas jar, preferably 2-3-L capacity - 3 M H2S04 a mixture of calcium carbonate (5 g) and sodium hydrogen carbonate (15 el [Thebicarbonate is added because it reacts more eficientl; than the calcium carbonate.]
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Journal
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5 M NH3aq, freshly prepared litmus solution teepol
The Demonstration Into t h e gas jar pour 200 m L water, 1to 2 m L teepol, a n d sufficient litmus t o color t h e solution. Explain t h a t this represents Johnny's stomach. To highlight t h e effect of t h e added sulfuric acid, add a drop of t h e ammonia solution before starting, t o i m p a r t a slight blue color.
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At (a) add ea. 10 mL of the sulfuric acid and swirl. At (b) add ca. 4 g of the carbonate powder. The mixture froths up and is stabilized by the teepol. At (c) begin tc add the ammonia solution while swirling the contents of the flask until the mixture turns blue. At (dl add sufficient sulfuric acid while swirling the flask to restore the red color. Finally, a t (4 add the remainder of the mixture of the carbonates.
