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in the Chemical laboratory Edited by NORMAN V. STEERE, 140 Melbourne Ave., S.E. Minneapolis, Minn. 5541 4
LVIII. Science Experiment Safety in the Elementary School CHARLES A. MANN, College of Education, University of Arizona, Tucson, Arirono 8572 1
The Editor of this column bolieves t,he ant,hor points up some of the teaching methods which may lead to a disregard for safety in the laboratory. Since readers of this column may wish to express their opinion to Mr. Mann, the twenty-two experiments to be evaluated in his survey are heing published here.
How safe are some of the science experiments being recommended for the elementary school? Twenty-two experiments recommended for the fourth, fifth and sixth grades are being evaluated by a group of shfet,y specialists in a survey now heing conducted. The survey analysis whieh will be reported later is part of a thesis which is in preparation. Safet,y specialists heing surveyed were recommended by the American Chemical Society, the American Society of Safety Engineem, the National Commission on Safeby Education of the National Edncation Association, the National Safety Council, and the National Science Teachers Association. The specialists were s k e d to judge the elementary school science experiments on the following criteria: EXTREMELY DANGEROUS: Activity too hazardous to be carried out in an average element,ary classroom wit,hant imperiling the health of persons present. VERY DANGEROUS: Activity so hazardous the teacher is required to have special undersiandings and to take proper precautions to execute the aet,ivit.y without jeopardiaing those present. AcMODERATELY DANGEROUS: tivit,y hazardous enough to eliminate student participation, but performed without risk by classroom teacher. LITTLE DANGER: Aetiviby with little hazard for the students when performed under teacher's supervision. SAFE: Activity snfficiently free of hasards so that students may proceed on their own with security. 1. Killing Jars. A simple killing jar for an insect can he made by using widemouth peanut-butter jars. Place a wad of cotton in the hotiom of each and cover the cotton with a round piece of cardboard or blotting papepel.. Saturate the cott,on with carbon tetrachloride or some
available insecticide containi!lg DDT. Nonpoisonous insect killing jars may also be purcha-ed from commercial scientific companies. The insect is killed instanily by placing it in the bottle and closing the top t,ightly. 2. Volatile Solids-naphtha crystals and moth flakes. Place some crystals, flakes, or mothballs in an open dish or box, after a few days, a reduction in size and amount is noticeable. Some children may have watched their mothers replace the moth killers whieh have gradually become volat,ilised. If a. pyrex tuhe is available, heat some naphtha. crystals over a st,erno or candle flame (CAUTION: these materials are inflsmmahle). Hold t,he tuhe with kitchen tongs or forceps and rotate slowly t,o keep the glass from becoming overheated in one spot and cracking. Watch how large, shining fern-like crystals are deposited upon the cooler parts of the tube.
3. Make charcoal. Punch a small hole in the cover of a coffee can with a nail. Obtain some soft pine wood and chop or cut i t up in small strips or pieces. Place t,he wood in the coflee can and cover the can tightly with the cover. Heat the can on a hot plate. smoke and gas will soon come through the nail hole. Wait a short while until all air has been driven from the can, and then try to light the gas coming through the hole. After a few trials, the gay will burn with a flickering flame. Continue heating the can for a t least '/* hour, and then remove the can from t,he hot plate and allow it to cool. Pull off the cover and examine the charcoal that has been formed. Repeat the learning activity, using either small pieces of soft coal or same paper toweling.
4. The carburetor. Place some alcohol or lighter fluid in an at,omizer and spray t,he fluid int,o the air once or t,wice to show how quickly the liquid becomes vapor when it is broken np into tiny droplets. Now spray the fluid over B candle flame located ahout 6 inches away, and note the vigorous, almost explosive flame produced by the rapid-burning fluid. (CAUTION: keep the children well away from the candle!) Point, ont that t,he esrhuret,or in an automobile also changes the gasoline into a vapor and mixes it with air t,o make a rapid-burning mixture.
5. Electroplating.
Put a heaping table-
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spoon of copper sulfate into a glass tumbler of warm water and stir vigorously until the copper sulfate dissolves. Then add a few drops of the solfnrie acid. Obtain bwo pieces of copper bell wire (No. 181, each piece ahont 24 inches long. Itemove quite a bit of the insulation from the end of one piece of wire and wrap n few turns of bare wire around one end of the copper strip, making s r m you have a good contact between the strip and the w~re. Bend the copper strip so it will hang over a pencil placed across t,he rim of the tumbler. Wrap the bare end of the second piece of wire around a house key and suspend the key in the copper sulfate solut,ion by wrapping the wire around the pencil. Now connect the other bare ends of both wires to two dry cells connected in series, making sure that the key is connected to a negative terminal and the copper strip is connected to s positive terminal. Allow tho current t,o flow for 15 minutes, and t,hen disconnect the wires and remove the key. The key will he coated with copper. 6. Electrolysis. Using the diagram of electrolysis setup; xdd as much sodium sulfate as will dissolve in a glass of cold water. (Sodiom salfate is much snfer than the sulfuric acid usually rccommended for this experiment.) If possible, secore stainless steel knife blades as suhstitnt,es for the carbon rods. With the current on, yon will notice that gm bubbles up twice as fast in the t,uhe connected to the minus hattery terminal (edge of battery) as it rises in t,he t,uhe connect,ed to the posit,ive terminal (center of battery). The electrode connected to the negative terminal generates hydrogen, while that connected to the positive terminal generates oxygen. To test for o y g e n , light one end of a slender wooden stlck or swab stick; then blow out t,he flame. While the tip is still glowing, put it into the tnbe where oxygen has been collected. Pore oxygen will make the n t flame. glowing tip b ~ ~int,o To test for hydrogen, plug the mouth of the tuhe under water with y o w t,homh. Remove the inverted tnbe. Hold a match near the t,uhe mouth as you remove your thumb. The small "pop" is the t,ypical hydrogen explosion. There is no hazard involved.
7. Gas and air. Punch a hole in the lower side of a coffee can which has a, tight,-fitting cover. The hole should be large enough for a rubber tuhe to fit in snugly. Now pnnch a. smaller hole in the cover of t,he can. Connect one end of the rubber t,nhing to a gas supply. Place the d h e r end of the tuhing inside the hole a t the side of the can. Turn on the ga? and let tho gas come into the can until yon are sure gas has displaced the air inside the can; (Conlinurd on pagr A348)
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then light the gas escaping through the h d e in t,he can cover. Now turn off the gas and remove the tubing. The escaping gas hums quietly a t first while fresh air is coming in the hole a t t,he side of the can. Soon the combination of gas and air reaches t,he proportions of an explosive mixture. At this point there is an explosion and the cover blows off. (CAUTION: This experiment should he shielded with fish net, screening, or wire gauze, and the children should stand well away.) 8. Examine blood. Wash your hands thoroughly and then rub a piece of cotton dipped in alcohol over one fingertip. Prick the fingertip with a sterilized needle and squeeze out a drop of blood. Press the blood against a clean microscope slide and cover with a cover glass. Observe t,he blood under the high power of a. micrascope. 9. Volcano. Invert a flower pot and cover i t with modeling clay to make a volcanic cone. In the crater insert a small porcelain evaporation dish or a small frozen fruit-juice can, 'whose sides have been cut down with tin snips so that the can is only 1'/* to 2 inches high. Surround the can completely with clay. Pour 1 tablespoon of ammonium dichromate into the crater. Cut a strip of magnesium ribbon 3 inches long and place i t upright into the ammonium dichromate so that one end is in the chemical and the other end extends above the crater. Now apply lighted wooden matches repeatedly (and patiently) until the magnesium ribhon catches an fire. If the magnesium ribbon is unavailable, put 10 drops of lighter fluid or alcohol on the ammonium dichromrtte crystals and apply a lighted match. The magnesium burns with a. hot, white flame and sets off a rapid chemical reaction in which the ammonium dichromate decomposes. The "volcano" erupts, sparks shoot up into the air, and a green fluffy material (representing lave) is formed. If the room is shaded or in semidarkness, the effect will he more pronounced.
10. Two gases form a solid. Fasten a small wad of cotton or paper toweling to one end of each of two paper clips or pipe cleaners. Dip one wad in dilute hydrochloric acid, the other wad in ammonia (ammonium hydroxide). Hang the clips on wires on opposite sides of a glass. A white cloud of ammonil~mchloride should form and eventually deposit a visible salt on the inside of the glass. 11. Chlorophyll.
(1) Use a coleus leaf. (2) Note the coloration. (3) Place t h e leaf in boiling water. In a few minutes, the red pigment will be extracted from the leaf. Now the green areas of the leaf previously hidden by the red pigment are revealed. Notice the nongreen, or white, area of the leaf. This white area does not contain chlorophyll.
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(4) Bail some alcohol on a hot plate. Drop the leaf from which the red pigment, has been previously extracted into the boiling alcohol. Chlorophyll is soh~hlein boiling slcohol, and in a few minntes the chlorophyll will be extracted from the leaf. Note that the leaf has become completely white. Remove it from the alcohol. ( 5 ) Now test for the presence of starch in t,he completely white d e n s leaf. Use a n iodine solution. Ilrop the iodine solotion all over the leaf. Note that the leaf toms black only in bhe areas in which the chlorophyll originally occurred. The black w e a indicates the presence of starch. 12. Volatile liquids-Solvents. With a medicine dropper place the same number of drops of such solvents as kerosene, torpentiue, nail polish remover, alcohol, and white gas in the centers of squares of blotting paper. Compare the speeds of evaporation of various chemicals. Be sure to have windows open and no flame in the roam (relate speed of evaporation to danger of explosive mixtures). The question of safety in the choice of cleaning solvents may arise. Place a. teaspoon of carbon tetrachloride cleaner in a metd jar top or paint,ing dish. Try igniting with a match. Taking necessary precaut,ions, repeat using only a. drop or two of a flammable naptha-type cleaner. Such experiments may mot,ivate careful reading and comparison of labels of many other chemicals used aromd the house, for example, insecticides which, because of their base, should not he sprayed nem open fires or hot snrfaces.
13. Equilibrium. Materials needed: water glass, 3 X 5 card, mercury, string. Cover the water glass with the card. Place a drop of mercury on the eard in a position near the center of the glass. Tap the card with enough force to quickly move i t off the glass. Ohserve the effect on the mercury. Does a change in t,he speed a t which you move the card change the effect on t,he mercury? Attach a strillg to the eard. Place the merenry on a hlack dot near the center of the card. P i d the card across a long table increasing its speed as yon pull, hut, keeping the mercury in its position. Stop the card snddenly. Observe the effect on t,he mercury. How do you explain the results y o u observed? 14. Flash explosion. Put some kerosene in an st,omiser and spray the kerosene across a exndlc flame. (Exercise cxntion.) The atomizer breaks the kerosene int.0 many tiny particles which burn wit,h an explorivo Rash. Keep children hack.
15. Soluble or insoluble. Add a few drops of oil to a. test tube containing water.. The oil will float on top of the water. Shake the test t,nhe vigol.ously. Although the oil may break ~ t pinto small drops, the drops will reassemble and the oil will contimle to float undissolved on top of the water. Repeat the experiment, (Conlinued a pagr A350) Volume
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- - 11si11g carbon tetrachloride inst,ead of water. This t,ime the oil will he dissolved. 16. Preparing
oxygen.
Using common
370 peroxide from the drr~gstmeprovides a safe and enyy way to separate the element oxygen from some of its compounds. The formula of peroxide, H 2 0 2 indicates that each molecule contains one more atom of oxygen than does s molecule of wate!., H 2 0 . T o extract this ext,ra oxygen, drop iron mst into a test tnbe or pill bottle of peroxide. Lower the container into hot water. Oxygen hohhles should he relensed from peroxide. P o ~ wperoxide on n cookie sheet or othor sheet of metal. Watch oxygen huhhlcs form. To lest. (agnio) for oxygen, lower a glowing, not flaming, match or splint, into ihe air space above the warmed peroxide in a t,uhe. The glowing wood sho~lld rekindle into a flame.
17. Making soap. It, is generally very easv for a class to collect enough bacon grease and other Eats to make a batch of soap. T o wash the grease, melt and strain into a kettle with 2-3 quarts of water. Bring to a boil, stirring frequently, cool unt,il you can lift off the fat. Repeat once or twice more. This removes salt and other sediments. Select only enamel ware, crockery, or iron vessels of shout 2 gallons capacity. Aluminum is not recommended. Use a wooden or stainless steel tablespoon or stick for stirring. Place the container on the gronnd and let the children watch the process from s standing position. This obviates any risk of their being splattered by t,he lye as you pour the contents of a can oery slow/?, into 2 pints of cold water. Stir until all is dissolved. Yon may wish to use njhher gloves and apron for extra safet,y. The solution becomes very hot became of the reaction between the sodium hydroxide and water. 18. Wet cell. Connect a strip of capper and a strip of zinc to a campnss-galvanometer. Place t,he metal strips (they should not touch) into s solution of dilute mdfwic acid. Will your electric cell light n flashlight h d h ? 19. States of matter. Materials needed: s,llfnr, 4 test, t,nhes, 4 corks for test tuhes, water, patassirm permanpanate, copper sulfate, or food coloring. Bum a very nmall a m m n t of solftrr i n a test tnbe. Close the tube with a cork. Breathe as few of these fumes as possible. Place s cork in mother of the test tubes. Fill the othor two test lubes with water. T o one, add food coloring or other mateT ~ I meh , as named ahovc, to produce a. h ~ i g h t l ycolored solution. Place a cork in each of these completely filled test tubes. Observe each lest t,nbe enrefr~lly.
20. The effect of the amount of oxygen on burning. Prepare some pure oxygen by pouring some hydrogen peroxide into a large tnmhler or glass jar. Add about a (Conlinurd on page ,4353) . .
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teaspoon of manganese dioxide and then cover the top of the jar with a n index card or piece of cardhoard. T h e hydrogen peroxide will decompose, bubbling vigorously, t o produce oxygen. (If manganese dioxide is unavailable, use sodium bicarbonate inst,ead. However, i t will now take longer for t h e peroxide to decompose.) Untwist one end of a piece of picture wire and hold this untwisted end in a flame until the wire begins t o glow. Then quickly insert the glowing wire into the jar of pnre oxygen. The wire will burn like a. Fourth of July sparkler in the pure oxygen. 21. Components. Materials needed: sodium peroxide, test tubes, wood splints, and water. With your teacher's help, prepare oxygen and observe some of its properties. Add 8. small amount of water t o a half teaspoonful of sodium peroxide. Observe the reaction. Insert a glowing splint into the tube. W h s t happens? What color is the oxygen? Is i t more dense or less dense than air? (CAUTION: Do not touch sodium perozide.)
22. Fine powder can. C u t or punch a round hole a t one end of a large metal can t h a t has a tight fitting cover. P o t a funnel into the hole from the inside. Attach a rubber tube t o the end of the funnel where i t comes out of the can. Set a candle a t t h e other side of the e m . Tilt the funnel so t h a t i t is aimed a t the candle wick. Place a. small wad of cotton in the bottom of the funnel and then add a teaspoon of lycopodium powder (or fine dry cornstarch). Now attach the other end of the rubber tube to a bicycle pump or use your breath. Light the candle and put the can cover on securely. Blow a blast of air sharply into the can. The powder, now a cloud of dust, is kindled b y the candle flame, hurning explosively. The resultant, sudden heating of the air, and production of gases blow t h e cover up into the air. (CAUTION: W h e n doing this ezpwimenl, be sure to have Ue children sland back.) The tin cover flies straight up, and i t is therefore wise not t o perform the demonstration under a light fixture.
The aotivities have been reproduced from the following textbooks with the permissions of the publishers: Aotivities 1 and 11 are from: Navarra, John Gabriel and Zafforoni, Joseph, Science Today for the Elementary School Teacher, Harper & Row. Put.lishers, Ino. New York, 1960. Activities 2, 6, 7. 10. 12. 14, 16, 17 and 22 are from: Hone. Elizabeth B.. Joseph, Alexander. Victor. Edward, and Brandwein. Paul F., "Teaching Elementary Scienoe: A Sourcebook for Elementary Soience," Harcourt. Braoe & World, Ino.. New York, copyright 1962 by Harcourt, Braoe & World. Ino. Activities 3. 4, 5. 8, 9. 15 and 20 are from: Victor. Edward, "Scienoe for the Elementary School," The Macmillan Co., NewYork. 1965. Activities 13, 19 and 21 are from: Smith, Herbert A,. Blecha. Milo K.. Sternig, John. "Science 5 (The Laidlaw Series)," Laidlaw Brothen, River Forest, Ill,, 1966.
Activity 18 is from: Sund, Trowbridge. Tillery and Olson. "Elementary Science Teaching Activities," Charles E. Merrill Publishing Co.. Columbus. Ohio, 1967.
