edHed by J. DUDLEY HERRON Pvrdue University West Lafayene, Indiana 47907
Recycling Disposable Plastics for Laboratory Use
Simplified Boyle's Law Demonstration
William C. Penker Durand Unified Schools Durand, ~ i & o n s i n54736
Daniel W. Miller 1250 Highway Auenue Couington, Kentucky 41011
A local veterinarian and the area ambulance service have provided us with a source of plastic bottles and clear plastic tubing. The veterinarian obtains vitamin and antibiotic solutions in 500-ml hottles of conventional and linear nolvethvlene (CPE; LPE). Normally, the bottles are disposed bf kter being emptied. hut we have obtained a laree " number of them for use in our lab and stockroom. Fitted with a *1 solid rubber stopper. .. . the hottles serve well for liquid storage, especially as desk-top reagent hottles in dace of the conventional dass-stoppered bottles. Thoueh not ideal, they can serve as containers for free-flowing solids. Fitted with a #1 one-hole stopper and 5-mm OD glass tubing, the CPE hottles serve well as wash bottles. The tops of the bottles can be easily cut off and used as funnels for both solids and liquids; the bottoms can he used for beakers and storage containers. The area ambulance service uses disposable oxygen masks fitted with 2 m of clear plastic tubing. After each mask was used, the entire unit was-formerly disposed of. Now, we have the ambulance attendants remove the tubing before disposal of the mask. The tubing has an inside diameter of 4.5 mm and an outside diameter of 5.5 mm. This tubing works best a t temperatures from O°C to 55%
The "discovery" of Boyle's Law is a popular introductory chemistry experiment. In recent years, a plastic syringe has replaced the cumbersome J-tube apparatus, eliminating the hazard of mercury spills. In the CHEM Study and other modern texts, the student employs a special syringe which has a platform attached to the plunger . on which one or more books or bricks may be placed to increase the pressure on the air in the syringe. The student records the volume as one, two, three and more weights are added, and by plotting pressure (in "number of weights") versus volume of air, the characteristic hv~erbolic ". -eranh . is obtained. This experiment suffers, however, because the student must take into account the fact that the total pressure acting on the air in the syringe is actually the sum of the pressures due t o the weights of the platform, the plunger, the weights, and the atmosphere. The student is then told that the weight of the atmos~hereis "eauivalent" to 1.7 bricks. Even thoueh this equivaience is usuhly developed in the text, I have fouid that students have a difficult time making the intellectual leap and generally regard the 1.7 bricks as some sort of "fudge factor" included to "make Boyle's Law work out right." This difficulty can be avoided completely by using an ordinary syringe placed inside of a bell jar which has been fitted with a dial-type vacuum gauge. A small volume of air (about 1ml) is sealed in the syringe at atmospheric Dressure and the pressure on the syringe is then reduced by the vacuum pump to 600, 500,400, 300 and 200 Torr. The product of corresponding pressures and volumes is clearly a constant value when rounded to the proper number of significant figures. The experiment can be rapidly repeated using other initial quantities of air to show that the relationship holds for any fixed number of molecules. This set-up further simplifies the student's interpretation of the data because the pressure exerted on the air by the weight of the plastic plunger is insignificant without the wooden platform attached and can be disregarded. The author will supply anyone interested with a copy of the student handout for this demonstration experiment.
A Very Inexpensive Source of Atomic/Molecular Models Charles F. Beck, Jr. Mount Lebanon High School Pittsburgh, Penmyluania 15228 Do your thrifty ancestors turn over in their graves every time you throw away the plastic eggs in which your (or your wife's) "L'eggs" pantyhose had been packaged? Save them to make models of hybridized atomic orbitals. Use a hot nail to melt two holes in the tip of the more pointed half of such an egg. The "twistem" that you saved from a lnat of bread will serve tn hold two (or more) halves together. After you've fastened the two halves topether use Dupont cement to reassemhle each egg. Two pairs with overlapping twistems properly twisted to assume the tetrahedral angle make a good sp:' model. Since these eggs come in several colors, you can vary the model to illustrate unshared pairs in sp" sp3d, or s p V d " models.
A Simple Lab Demonstrating Energy Transformation Daniel W. Miller 1250 Highway Auenue Couington, Kentucky 41011 Introductory chemistry courses customarily include a discussion of energy somewhere near the beginning of the course. Seldom, however, is the student given the opportunity t o inVolume 54, Number 4, April 1977 / 245
An Experiment in the Characterization of Coordination Compounds Ihring the pa31 ten y r a n there have heen numerousexperiments \\hic,h :nwlve the synthesisand chnrnrteri~ntionof cwrdination compounds.' In the mam theseexperiments are performed w r r twuur thrcr lnh dnya. Ofren rttrntlons, rnuleuular weight and spectral data are used to elucidate the structure of the compound. In an attempt to produce a shorter experiment whsh employs more techniques, a new experiment was developed. The student is given an unknown coordination complex and asked to identify it, using both chemical and physical data. The student is given 500 mg of a sample that contains one of the following compounds:
Not all of these compounds were employed. Qualitative analysis is performed to determine which ions are inside and outside uf the coordination sphere of the complex. Care must be taken since some tests, such as thedetermination of NOr- with diphenylamine and sulfuric acid'destray the complex, and thus the test does not differentiate whether or not this ion is inside or outside the coordinate sphere. T o test for NHa or ethylene diamine in the coordination sphere, asodium hydroxide solution is added t o the solid, the mixture heated, and the gas tested with moist long-range pH paper. Other components inside the coordination sphere can be detected after the complex is destroyed by heating in the presence of dilute sulfuric acid. Next, a 35-mg sample of the unknown is dissolved in 40 ml water and the conductance of the resulting solutions measured. The student is expected to determine the number of ions present by comparison with a table of conductance data. The table is set up in such a manner that the student isgiven an estimate of the charge type but is not able to obtain an exact answer since the expected values are based upon an average conductance for 35 mg of sample for an average molecular weight of the possible unknowns. Finally, the spectrumof thesolution of the unknown is measured a t successive 50 nanometer intervals from 350 to550 nm. After plotting the spectrum, the student is expected to compare the spectral peaks with those of [Co(NH:MI]Clrand [Co(enhNO&I]NO:i. Other experiments have involved the matchingof spectra of known spectra with those of an unknown. Our expectation is to have the student interpret the spectral peaks in terms of the spectroscopic series. Students are asked to determine whether strong-field andlor weak-field ligands are present in the complex.Comparison with the two reference spectra gives the student a more specific indication of the ligands present. After all of the experimental work is completed, an identification of the compound is made based upon all data. One t o two 3-hr periodsshould be allowed for thecompletion of the work. A 4-hr lab would be ideal. We have one Spectronic-20 for 8-10 students and one conductance bridge for the entire section of 40-45 students. Copies of the directions given t o the students are available upon request. 'Creswell. C. J.. "Modular Laharaton Proeram SYNT-095." Willard Grant Press. Boston. 1972. Burmeister. J. L.. and Jovanovich, Inc., New York, pp. 105-113. 2Grotz, L. C., J. CHEM. EDUC., 50.63 (1973).
The College of Wooster Wooster, Ohio 44691
246 / Journal of Chemical Education
T. R. Williams L. W. Haynes
