GEORGEL. GILBERT Denison University Granville. Ohio 43023
A Fluorescence Lecture Demonstration SUBMITTED W Joseph W. Bozzelli Department of Chemical Engineering and Chemistry, New Jersey Institute of Technology. 323 High Street. Newark. NJ 07102 CHECKED BY
Marwin Kemp C/O Amom Production Company Tulsa Research Center Tulsa, OK Figure 1. Detailed diagram for electraniG changes during fluorescence. There are many lecture demonstrations available1 for the general chemistry course, and, in fact, there is not enough time to perform all the demonstrations one might wish to and still cover the material in the course. There is, however, a relative nnucitv of lecture demonstrations available and = - ~ ~in~the - ~number ~ " relevant to the illustration of atomic and molecular theory-a tonic which has been included in the eeneral chemical curricula over the past several decades. fluorescence demonstration can be easily related to several aspects of molecular theory and quantized energy levels. The brightly colored glows readilv attract the student's interest. A selection of fluorescent chemical solutions which have luminescence properties spanning the visible spectrum are used for a series of demonstrations. The demonstrations use 4-6 different solutions each of which fluoresce a t a significantly different wavelength (color)2 (see table). For the first ~
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Fluorescent Dye Solutions *
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COIW
Fluorescein Rhodarnine B Rhodamine 6G Eosin yellow Nile Blue A b Coumarinr Bis MSB (pbis(o-methylqryi)benzene Phorwited
G-een-Yellow Red
Orange Yellow Red
Green BlueViolet BlueWhite
0.2 10 2.0% in 50150 e ~ ~ l l w a tsolvent. er Available from J. T. W w . 'Obtain& horn MCB Reagents Go. a obtainedtmm mbsychemical, Sbln mision, sayonns,N.J.
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demonstration, the dye solutions in 500-mlErlenmeyer flasks are lined un on a table in front of the lecture class. The room i$ darkeneh and the students are asked to note the dark solutions on the bench. A lone-wave ultraviolet lamp3 is turned nn, and its faint violet glow is demonstrated for a few seconds. The uv lamp is not aimed directly at the students. The lamp is then placed alongside each flask for several seconds, and the strone fluorescence (elow) at different wavelengths from the variez solutions is observed. An explanation on absorption of the uv radiation from the lamp, vibrational decay in the excited state, and final reemmision (fluoresence)* a t longer wavelengths, lower energy (visible light in this case), is then presented to the student as illustrated in Figure 1.A somewhat less detailed explanation can be given should it be desired, using a three-level diagram of a molecule's energy states, as shown in Figure 2. The instructor might, in addition, explain that this uv absorption and fluorescence (emission) are the first several steps in ob-
Figwe 2. A simpler diagram for iliusbatbnsflus-ce. The phnms emitted by the excited species are lower in energy (longer in wavelength)than those absorbed, because some energy of the excited species is transferred to the solvent molecules through coliisional processes tainii the stimulated emission (lasing) of a dye laser,&should
he be familiar with this material. . An additional fluorescing demonstration is now performed in the same manner as above. This one uses two additional solutions: one of Alconox, a wmmercial chemistry laboratory glawware cleaning detergentQnd the second of any common household type laundry detergent? containing brighteners or whiteners. Both of these solutions will fluoresce with a hluewhite lominescence: .~ ~ ~ . . , the Alconox will be cousiderablv weaker, illustrating the large scale use of fluorescent materids in home consumer products. Tbii point is further amplified by getting the students to discuss and identify fluorescence with the bright emission from clothing on some of the patrons at a disco they may have attended where ultraviolet or black lighting is utilized. The concept of why clothes which have brightners added are perceived as being whiter can be explained to the studenta from this demonstration. In essence a white object merely reflects all (almost) the visible lieht that is illuminating it, while a brightened white ohject reflects this visible ill"minatine lirht d u s it emits additional liaht from the hrightner mole&& conversion process (uv to visible), as long as there ~~
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Alyea, H. N.. and Dutton, F. 6.. "Tested Demonseations in ChemEDUC., Easton. PA., 1985. istry." 6th Ed.. J. CHEM. A Number of differentdyes and the wavelengths at which they fluoresce can be obtained from companies which sell dyes andlor dye lasers, or the fluorescent section of the MCB Reagent Catalog. MCB ManufacturingChemists Inc., Cincinnati. Ohio. A long-wave, uv Black Lamp is utilized. Streitweiser, A,. and Heathcock, C. H.. "Introduction to Organic Chemirtrv." .. ,. Macmillan. New York. 1976. Oshea, D. C., Callen, W. R.. and Rhodes, W. T.. "An lntroductlon to Lasers and Their Applications," Addison Wesley, Reading. MA.
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" Alconox Detergent. Alconox Corporation, New York, NY 10003. Distributed by SGA ScientificCorp., Bloomfield. NJ. 'Any household laundry soap solution such as ERA@,CheeP, or a
bleach with brightners such as Borax', will fluoresce. Volume 59
Number 9
September 1982
787
is some uv light present in the illuminating source. More photons. therefore. emanate from the briehtened ohiect than the nonbrightened, making it appear whkw. The difference in enerrv hetween the uv lieht ahsorhed and the visihle lieht emittezis converted into (eat within the object and is tipically too small to notice.
into the chlorine in one of the cylinders. Observe a vigorous reaction and a phosphorus chloride cloud develop in the cylinder. Cover, take the spent reactants to an efficient hood, and leave uncovered until excess chlorine is gone. Attach the steel wool to the length of wire and lower into the chlorine in the other cylinder. Spontaneous comhustion with copious brown FeC13 smoke is observed. Dispose of excess chlorine as before.
Spontaneous Combustion of Familiar Substances in Chlorine
Remarks These are simple, inexpensive ways of demonstrating spontaneous comhustion in chlorine that can he used in addition to the well-known sprinkling of tin or antimony powder. Note that the products of antimony combustion a r e toxic. These reactions are visible to a large audience and release a minimum of chlorine. The reaction of phosphorus with chlorine can produce two phosphorus chloride^.^ (Note that the striking strip, not the match head, contains red phosphorus.)
SUBM-D
BY
Thomas S. Briggs Lowell High School 1101 Eucalyptus Drive Sm Francisco. CA 94132 CHECKED BY
Erwin Boschmann lndlana University-Purdue
Indianapolis, IN 46202
Unlverslty
Preparation Obtain 5%NaOCl (liquid bleach), 6 M HCl(40 ml), moist red phosphorus (0.1 g) or a large match hook, grade 00 very fine1 steel wool (3 cu. in.), two 2-L graduated cylinders with Petri dish covers or glass plates, and a 2-ft length of wire (#22). Demonstration Add 50 ml of 5% NaOCl to the graduated cylinder. On a demonstration bench n e a r a hood o r ventilated a r e a add 40 ml of 6 M HCI. Cover the cylinder, shake, and note the chlorine that fills the lower half of the volume. Repeat the above in a second 2-L cylinder. Fasten the match book or paste some moist red phosphorus on the end of the wire and lower
788
Journal of Chemical Education
Reaction of steel wool with chlorine is known to produce ferric chloride.3
'American Steel Wool Mfg. Co. Inc., Long Island City, New York 11101.
Mellor, J. W., "A Comprehensive Treatise on Inorganic and Thewetical Chemishy," Volume VIII, Longmans, Green and Co.,New Y&. 1928, p. 785. Ref. (2).Volume XIII. 1934, p. 314.
