GARYE. DUNKLEBERGER Carroll County Public Schools
Student Preparation for Prelab Sessions Judy Smith 11627 River Oaks, Austin, TX 78753
The lab instructor's dream: Students arrive for the prelah session having read the background information and procedure for the experiment; their questions about the experiment shaoe the orelab session and involve each student. T o accomplish thisgoal with high school chemistry students, I begin two days before the experiment with a prelab homework assignment, followed the next day by a class discussion based on that homework. Below are the details of this prelab sequence. Two Days before Lab: Homework (1) Read
the experiment, focusing on background information and procedure. (2) Write five "lab questions" related to the background information andlor procedure of the experiment. The key to the homework assignment is the writing of questions. In reading the experiment, the student will he puzzled by an unfamiliar word or concept, a new procedure, or an unclear lab instruction. Through his or her lab questions, the student asks for clarification of those aspects of the experiment that are puzzling. The student is forced to read the experiment in order to write the questions. Examples of lab questions submitted for the determination of the molar volume of hydrogen gas by reacting hydrochloric acid with magnesium include: (1) What is an eudiometer? (2) Why should the acid and the water not be mixed together in the eudiometer before adding the magnesium? (3) Why does the hydrogen made in this experiment stay inside the tube and not escape into the air? (4) Would the results of the experiment change if I used too much acid? (5) Why do we use HCI and not some other acid? As these examples show, students request information ranging from simple definitions (question I), to clarification of lab procedures (questions 2-4), to more probing inquiry into the design of the experiment (question 5). Day before the Lab: Prelab Sesslon
At the beeinnine of class I collect the lah auestions and read aloud one question from each paper. A single question from each paper doesn't usually cover all the good questions nor does it allow for reinforcement of important concepts. Thus, I usuallv. exnect . and receive two to three rounds of questions. The Woes of questions I look for in the first round concern essenti~ldefinitions,concepts, and lab manipulations. After reading an individual question, I encourage the students to respond with what they think are likel; answers to that
question. Often students will respond to a question of lab procedure by suggesting several workable solutions. In discussing the alternatives, the students begin to realize that choices of specific procedures are more open-ended than might he suggested by typical high school lab manuals. T o help them choose among the alternatives, I guide the students in trying to foresee the advantages and disadvantages of their suggested methods. Although students tend to have ready answers to simple lab questions, guidance from me is usually required in the more complex cases. One round of questions usually covers every important lab idea a t least once. In the second round, I include questions that probe more deeply into both the design of the experiment and the chemical principles involved. Students may ask why a particular sample size is used or why an evaporation is done overnight rather than during the lab period. Such questions bring up matters of economy, precision, and reaction times-ideas that seldom occur to beginning students. However, so that concern for these less obvious matters dnrs not distract their attention t'rom [he main ideas of theexperiment. :n thesecond round 1 altrrnatr"dt.ep"questions k i t h basic questions already discussed in the first round. Repeating the basic questions in the second round allows the student to hear different ways of asking the same questions, and, hy the second round, gives the student a chance to answer these auestions in his or her own words. The prelah questiousmust be graded to be effective. T o receive full credit, their questions must also be appropriate. Students do not receive credit for trivial questions, but what counts as a trivial question depends on the level of the class. To clarify for the students what is acceptable, during each prelab session I call attention to particularly good questions and also cite a few unsuitable examples. The main value of using lab questions to prepare for an experiment is specificity: T h e questions cover information that this particular class needs to know right now in order to understand and nerform the exneriment successfullv. Lab questions remind me that information that I take for granted is indeed new to a beginning chemistry student. Such a reminder is important, because I would not include in a prelah session information that I considered common knowledge. To the student, however, alack in his or her "common" knowledee makes incom~rehensiblean otherwise simple procedure. Lab questions generate interest. Students enjoy hearing their questions read and answered, and they like being able to answer each others' questions. Since I never know exactly what will he asked, their questions interest and challenge me as well. This unpredictable character of lab questions appeals to the students also, since they cannot foresee the Volume 64
Number 7
July 1987
621
questions their classmates will ask. They learn to recognize insightful questions and occasionally salute them with comments like, "How did he ever think of that?!" Such a response can lead to a discussion of how to ask good questions in science, how to analyze a lab procedure critically, how to do creative scientific thinking.
622
Journal of Chemical Education
The lab question technique has given my prelah sessions both immediacy and interest. Best of all, in the same time as a conventional prelab discussion, I not only cover the usual concepts and techniques hut also teach students how to ask the probing questions that get to the heart of experimental design and scientific thinking.
