James M. Thorne Brighom Young Un~versity Provo, utoh 84601
Condensed Laboratory Experiences for Nonmaiors
A number of chemistrv courses for nonmaiors do not offer any laboratory experience to the students. The resultine loss of touch with realitv can he a serious deticiency. F& instance, students whishow considerable skill in balancing equations sometimes have no concept of an equivalence point or the possibility of a reactant being present in excess. One could cite numerous other examples which could be readily corrected in proper laboratory setting (1). But laboratories are expensive, time consuming, and often paced too slowly to maintain student interest. This article suggests a compromise which gives the nonmajor what he needs in a short time with low cost in terms of teaching facilities and personnel. The approach is to have students in small groups spend an hour in the laboratory a few times during the term. While there, they do not perform traditional laboratory experiments, hut rather are guided through a carefully chosen series of hands-on demonstrations. These demonstrations require far less student and professorial time than traditional exoeriments and so allow much more efficient instruction. They are not as fast as lecture demonstration, hut have the advantage of providing the student with a more personalized experience with the physical materials of chemistrv. In addition, they demand individual, self-paced responses of each student at each step in the analvsis of the demonstration. Such responses are difficult to elicit in a large lecture section. Objectives The objectives of the hands-on demonstrations are 1) To pmvide the student with fint-hand experience with the laboratory materials of chemistry. 2) To provide physical reference for the concepts discussed in
lecture (mole. concentration. reaction rate. etc.).
3) To reinforcelecture information and calcuiatio~s. 4) To awaken students' curiosity in chemistry.
Hands-on demonstrations lend themselves well to the implementation of behavioral objectives of the type described by Wolke (2). That is, they make it evident when the student has correctly extrapolated, classified, asked the next significant question, etc. Because of their standalone nature, they should also fit well where the Keller Plan is heing used. Students could go through the hands-on demonstrations before the topics were discussed in class so they would have a physical system in mind to help them understand abstract concepts. Or, the students could go to the laboratory after lecture when they are better prepared to appreciate the quantitative aspects of the demonstrations. Or, the same concepts could be demonstrated in two different ways andgiven both before and after the lecture on the corresponding topic. There is a very strong temptation for the teacher to choose his favorite, impressive demonstrations and force the objectives to fit them. Better results are ohtained by planning the objectives first and then facing up to the tnsk of finding (or developing) the demonstrations which adequately fulfill the objectives. However, most of the demonstrations can be extended for the optional use of 114
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the curious or advanced student. The favoiite flashy demonstration canoften find an appropriate place here. Helpful information regarding the sequence of topics which may be covered by demonstrations can he obtained from the order of topics in textbooks or from articles on integrated laboratory programs (3, 4). Most lecture demonstrations can he scaled up, and many traditional laboratory experiments can be scaled down to become effective hands-on demonstrations. An annotated bibliography of such experiments will he sent on request. Sealed tube experiments (5) and tested demonstrations (6) are especially useful. Very often, a piece of unused apparatus can become the heart of a demonstration which can have considerable impact upon the senses. For instance, a surplus, handcranked electrical generator was wired to a light bulb to demonstrate conversion of mechanical energy to light. Even the football players in the class had difficulty generating much light. This was contrasted with the impressive brilliance of burning magnesium ribbon which led to an appreciation of the energetics of chemical bonds. Discussion then moved to the topics of efficiency and non-renewable resources. Hands-on Demonstrations The demonstrations are designed to reinforce the concepts covered in lecture with emphasis on maximizing the sense content (sight, smell, hearing) to improve retention by the student. The demonstrations are alieady set up as the students enter the laboratory. While setting-up is an experience which should definitely not be missed by those majoring in chemistry, i t can distract nonmajors from the main points of the demonstration. In the hands-on demonstrations, the student is given written instructions in the manipulation of the system (e.g., how to perform a crude titration with an automatic-filling buret). Dispersed among the instructions are questions which are to be answered (as in programmed learning texts) and turned in for grading a t the end of the period. The demonstrations are designed to cover the main concepts of chemistry auicklv and svstematicallv. The followine is a verv brief description o f t h e demons&ations in a sequence which has been found to require aoproximatelv one hour of the stu.. dent's time 1) Samples of
elements and compounds for observation of color, smell, density, and physical appearance. These serve as an introduction to the materials used in chemistry and help to correct the "silver-chloride-is-a-pale-green-gas"syndrome. 2) A weighing exercise which introduces the need for the mole concept. 3) A comparison of dyes in solution to provide a visual insight into concentration differences. 4) A titration to demonstrate ciiemical reaction and the equivalence point. 5) A time-lapse tape recording of radioactive decay as manitored by a Geiger tube. This gives an audible record of reaetion rate decrease as a function of time. 6) An iodine clock reaction with instructions for students to perform a series of dilutions to show the effect of concentration on reaction rate.
Details of these demonstrations will he sent on request. The titration will be described in detail to show how the objectives of this condensed laboratory experience are met. In this reaction, 0.01 mole of CaC03 is titrated with 1.0 M HCI. The demonstration is already set up, including the weighing out of the CaCOs. Congo red indicator is added to the acid in the flask that feeds the buret. The student is told that the violet color indicates an Hi concentration of more than 10-5 M. After adding a few ml to the dry powder in an Erlenmeyer nask, he is asked to observe the color and comment on the H+ eoncentration. Both the red color and the remaining CaC08 powder make it evident that the H+ is not yet in excess. The student then calculates how many ml are required to deliver 0.01 mole of HCI, and adds this volume to the flask. Vigorous bubbling occurs as COa is released, but powder remains and the color is still red. He is then instructed to add acid until the color changes. This, of course, turns out to be 20 ml (0.02 moles). All of the CaC08 has dissolved at this point, providing added evidence that the equivalence point has been passed. The student can now give evidence that a chemical reaction has taken place, and can halanee the corresponding equation with the full realization that excess CaCOs existed up to the equivalence point, and the H+ was in excess thereafter. The extension of this demonstration can pmceed in any one of anumher of directions. A few possibilities are listed below 1) The questron of reversing the reaction could be raised, bringing the student to realize that the Con gas had escaped. He could then go on to show the Cat+ had not escaped by precipitating some of it with a NaaC03 solution. The return to red indicator could also be discussed. 2) A solution containing a dissolved base could he titrated to
show the technique was not restricted to visible powders and to provide more practice in calculations involving concentrations. 3) The normality or equivalent weight of an unknown could be measured. Conclusion
Student comments indicated enjoyment of the demonstrations, and no boredom was detected in this fast moving laboratory. Many students were frankly delighted with the chemical phenomena under their personal control. It was noted t h a t there was a modest improvement in the final exam scores of those who went through the demonstrations. In conclusion, it appears t h a t in t h e ecosystem of chemistry teaching, there is a niche for hands-on demonstrations for nonmajors. T h e demonstrations discussed here are inexpensive in terms of teacher supervision, laboratory space, and equipment. Students enjoy them because they move fast and appeal t o t h e senses. These demonstrations have been a valuable addition t o our chemistry course for nonmajors. Literature Cited 11) Momll, W.E.,J.CHEM.EDUC.. 30,8011953). 12) Wo1ke.R.L.. J.CHEMEDUC.50,101(1973). 13) Coehran,J.C., Lewis, D. K.,Sfagg. W. R., and Wolf,
W.A,, J. CHEM. EDUC.,
Volume 52, Number 2, February 1975
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