A General Chemistry Demonstration: Student Observations and Explanations Robert G. Silberman State University College, Cortland, NY 13045 Recently in my second semester general chemistry lecture, I conducted a teaching experiment that had results which are interesting and disturbing for anyone who teaches general chemistrv. I Derformed a demonstration. listed all the chemicals inv&eb, and offered an exam bonus to anyone in the class who described and correctlv exolained the chemistrv involved in the demonstration. 0;t of'the 70 answers turnei in. one was correct and about 10 were ~artiallvcorrect. The remainder of the answerssuhmitted weie eithe;totally wrong or showed maior errors in understanding. ". com~rehension. andlor reason&. The demonstration I used has been called the oranee tornado and was developed by R. S. Ramette.' I used only one half of the demonstration, i.e., mercuric iodide and mercuric iodide complex formation. The Demonstration A 4-L beaker containing 3.5 L of distilled water and large magnetic stirring bar was stirred at the rate that caused a smooth vortex to form. Next, 35 ml of 0.1 M mercuric nitrate was added with enough 0.01 M nitric acid to prevent the formation of hydroxide andlor carbonate precipitates. Small portions of 2 M potassium iodide solution were added in the center vortex causing a precipitate of HgIz in the form of an "orange tornado'' that gradually dissipated as stirring continued. The tornado can be formed or dispersed a few times until there is enoueh iodide in the svstem to cause a mercuric iod~dcprecipitatt: todisperse throughout the sptem. At tllis ooinl. KI is add14 at the ~crirneterof the beaker. Eventuallv the ~ g 1 2will dissolve, wi'th its tornado disappearing last, as the I- concentration increases enough to form amercuric iodide complex which is soluble and almost colorless. In mv class. as I carried out the demonstration. each chemicni and p w e of equipment was listed on the blackboard alnnr with order in which i t was added or used.Thestudents werenked t u drxribe the phys:cal demonstration and explain the cht.mistrv of t he ohenornenon. Th6,students were allowcd to use textbooks or iihrary sources but were asked to pledge that they had neither given nor received help. The demons t r a t i t i w a s periormed after the follming t&,its had been discused: acid-hase equilibrium, soluhilily ~ r o d ~and s t K.., redox equilibrium, and a reasonable amount of descripti& chemistry. The class was three-quarters of the way through a one-year general chemistry course. The quality of the answers handed in by students was disturbing and very disappointing. The answers showed the students' inability to research a topic or generate a new approach to a puzzling situation. Some of the student answers are reproduced a t the end of this paper. The students' explanations were characterized by five kinds of difficulties. Concept names of various hinds were invoked with little aooarent understandins of the conceot. "Jarmn" ran wild. he concepts included ambhoteric, di~proport&nation,redox reactions, acid base ionization. acid base hvdrolvsis. cation. anion interaction, pH indicators, buffer action, buffer hydrolysis, polyprotic acid behavior, and LeChatlier's Principle. In short, almost all the words and phrases we regularly use and define in our lecture appeared in the student answers. The students have easily adopted the terminology but have only the vaguest understanding of the concept described by the 996
Journal of Chemical Education
term, or how the term is used in chemistry. Contradictory statements abounded in the explanations. The first statements in the explanation were often contradicted by the last few statements in the same explanation. The students seemed unaware of the contradiction. The extreme case: "HN03 acts as an acid." A few sentences later in thesame paper stating that "HN03 is basic." The exolanations showed a n inabilitv to consider a new approach or to explain o phenomenon that tlwy had not seen brlore. Almost all the students invuked ideas in chemistrv that thpy had aeen before. i . t , , acid-bast, hehawor, redox reaciions, hutfer am~hoterlsm.etr. 'The students seemed to hend anv concept tdexplain what they had seen and then made up ne& and seeMinalv stranee (to us) chemical eauations to s u.~.o o r t their hypot&es. F& example,
+ 2Hg0 + HIO
-
Hp(H30)2++ KI
-
41-
HgO + HgIn + 2HOI
Hg(Hp0)1+~+ KI-
(orange)
There was apparently an almost total unwillingness or inability I'm not sure which) to attempt to discover what occurred by sorting out the relevant material in a textbook or other reference in the library. It all seemed to be made up in the students' heads. A lack of familiarity with properties of common chemicals was shown, as evidenced by the statements such as HN03 can he a base in aqueous solution, KI is an indicator that turns yellow in base, KI is a strong base, iodine is bright yellow, etc. I t is difficult to decide what to make of the results of this experiment. Clearly beginning chemistry students have difficulty integrating what they have seen and what they have studied. Some of these difficulties can be traced to poor reasoning skills, some to poor backgrounds in descriptive chemistrv. some to unskilled teachine. and oerhaos some to p w r attitudes toward the intellect~~al'~halleI;ge of>hemistry. Studies haveshown th:it 70%ofthcstudents takine- frrshman chemistry are not at a formal reasoning level in Piaget's framework of reasoning levels. The contradictorv statements. incorrect use of ana~dgy,and selected use of bbservations found in the answers represent the kinds of erroneous thinkine strategies used by those individuals who have not reached the highest levels of reasoning ability. It is difficult to say exactly what a lecturer can do to improve student reasoning levels, although a number of individuals are developing new programs with this aim.'-4 One area that we
' Ramette, R. W. in "New Ideas and Exhortations for Using Demonstrations in Teaching Chemistry." Shakhashiri. B. and Dirreen. G. E. (Editors)Presented in part at the 6th Biennial Conference in Chemical Education. Rochester. NY in Auaust. 1980. ~uller;R. G. (~diior)"~iageiian~rograms in Higher Education." ADAPT. Lincoln, NE. 1980. Ryan, M. A., Robinson, D., Carmichael. J. W., J. CHEM. EDUC.,57, fid? - .- l l.9-R-O-I,. 'Silberman. R. G.."Cognitive Labs in Chemistry," presented at the 2nd Annual Conference on Reasoning. Piaget. and Higher Education. Metropolitan State College, Denver, CO. 1981. \
may he able to do something about is the use of incorrect names and phrases in student descriptions. In part we are educating our students to use, and rewarding them for using, short descriptive words or phrases by giving multiple choice tests and short answer exams. Students learn when to use a phrase to answer an exam question, hut they may never understand the concept the phrase describes. We accept such answers because we understand the meaning of them and assume, incorrectly, that our students understand the same meaning. We seldom ask our students to explain anything in simple terms. If we do ask them to explain, the students become tongue-tied and frustrated, or else cloud the air with a dense fog of undefined or poorly understood phrases as the students' answers below demonstrate," I believe we can improve things by asking students questions that cannot he answered by a single term or phrase hut require an explanation. By restructuring our lecturers, laboratories, and recitations we can ask and encourage students to explain observations and discuss experiments or demonstrations rather than simply solve a numerical problem, supply a missing phrase, or obtain a numerical value. The observation that students do not seem to understand demonstrations should not be used to justify eliminating demonstrations. Rather, it points out the need to do more and better demonstrations and to question students' understanding in order to improve student observational and interpretive skills. Selected Incorrect Student Answers Example # 1 Problem. Explain what is happening chemically and physically in this demonstration. Physically. Three and a half liters of water are on a rotating platform, causing a whirlpool to appear in the middle. Next, 35 ml of 1M Hg(NO3)zsolution is added, causing the solution to turn orange. To make the solution turn clear again, some HN03 is added. Now a few drops of 2M KI are added. As this is added, the tornado turns orange at the bottom and then the orange color disappears. Add more KI. and eventuallv the whole solution turns lieht mmgr. tlr:u~gp.;,ranre-red. ;mil :ilm~,-trnl. Suddenly it turn> clear uram ;~ddinc I. \\'t.:~ret d d thi~tYOU a n n o t r e r ~ r " tncm I< this demonstration. Chem~callv.Water with He(NO9)9causes it to ionize. The ionized ~ g +
