Author(s): Michael S. Pritchard, Department of Philosophy, Western Michigan University & Theodore Goldfarb, Department of Chemistry, State University of New York at Stony Brook
NOTE: This contribution appeared as a featured resource in the online and printed issues of ENC Focus: A Magazine for Classroom Innovators Vol. 8 no.3, published by the Eisenhower National Clearinghouse for Mathematics and Science Education-ENC.
Heidi Gross, Oyster Bay High School, Oyster Bay, Long Island, NY
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In school science laboratories, students frequently will know what the expected correct result is before doing an experiment. In such cases, students who err in carrying out the experiment may realize that the data collected is not consistent with the expected result. This often leads students to alter their data, rather than report a result they know is wrong. This case study lesson is designed to teach students why altering data is not acceptable behavior on the part of scientists or science students. Give students the homework assignment of reading the case study Making the Data Fit the Result, and writing about their reactions to the behavior of Mike and Sarah. In class the teacher should lead a discussion using the following questions as a guide.
With the teacher's help the class should write a set of guidelines for proper behavior in conducting laboratory experiments and reporting the results.
Jon and Sarah are laboratory partners in Ms. Joule's physics course at Central High. The laboratory for the day is the determination of the identity of an unknown metal by measuring its specific heat. Ms. Joule has told the class that each pair of partners' unknown metal is either aluminum, lead or zinc. As instructed, Jon and Sarah use the top loading balance to weigh a styrofoam cup, which will serve as a simple calorimeter. They then fill the cup half-way with water and weigh it again, subtracting the weight of the cup to calculate the weight of the water added. In the meantime they have placed their unknown sample in a beaker of boiling water. They use a thermometer to verify that the temperature of their sample is now 1000C. At this point, thinking that they have plenty of time they get into a conversation with another pair of students in the class about a school basketball game that they all attended last weekend. They then measure the temperature of the water in the styrofoam cup and find that it is 270C.
Next they remove their metal sample from the boiling water and transfer it to the styrofoam cup and begin measuring the temperature of the water in the cup. After a few minutes the water temperature has stopped rising and they record this as the final temperature. Realizing that they forgot to measure the mass of their unknown sample and that they must now hurry to complete the lab before the end of the period they transfer the sample to the balance, but forget to dry it. Therefore the mass they record is significantly higher than the true mass of the sample. Not realizing their error, they proceed to calculate the specific heat. They note that Ms Joule has told them that they can ignore the very small amount of heat that will be absorbed by the styrofoam cup. They make use of the following formulas from their lab manual.
Heat Lost = Heat Gained(mcT)unknown(mcT)water(mc)unknown[212 - Tfinal] =(mc)water[Tfinal - 27]m = mass; c = specific heat; T = temperature change;cwater = 1.00 kcal/kg0C. The value of the specific heat they calculate for their unknown is 0.14 kcal/kg0C Using the Handbook of Physics and Chemistry they find the following values for the specific heats of aluminum, lead and zinc: caluminum=0.22, clead=0.035, czinc= 0.087.
From the appearance of their unknown they are certain it must be aluminum. It seems to be a light weight (low density) metal like aluminum, but unlike lead or zinc. However their result is closer to the specific heat of zinc than that of aluminum.
Mike and Jon discuss what to do. They could acknowledge that they realize they must have made some error in measurement and explain why they think their unknown is actually aluminum. Instead they decide to alter their data. Substituting the true value of the specific heat of aluminum in the equation, they solve for the value of Tfinal that would give the correct result, and change the value of the final temperature in their lab data to that value. They then hand in their lab report to Ms. Joule.
In the context of an informal classroom discussion students will usually admit that the changing of lab data to fit an expected outcome is a type of student behavior they have observed. If they know that there will be no negative personal consequences, many of them will also admit to having changed data themselves in the past. Although most of them will agree that what Mike and Sarah did was theoretically unethical, many will acknowledge that they would probably do the same thing if the odds of getting caught are low. Students will frequently try to justify this behavior by distinguishing between what goes on in a school laboratory and real science.
Convincing students that they should abide by the same ethical standards with regard to collecting and reporting data as is expected of professional scientists is not an easy task. Explaining that a key purpose of the classroom laboratory is for students to learn to model all aspects of proper experimental procedure becomes much more difficult if the laboratory exercise is structured in a way that focuses primarily on getting the correct result. For this reason considerable attention to question (d) is likely to be very profitable, particularly if the result is a restructuring of the laboratory lesson in a way that emphasizes good procedure, and removes the motivation to alter data by greatly decreasing the credit accorded to obtaining the correct result.
The final task of developing a set of class-generated guidelines for proper laboratory behavior will usually prove very valuable. Once having constructed their own guidelines, the students will tend to think of them as something they have ownership of rather than as a set rules externally imposed on them.
Return to Part 2 - Model Classroom Lessons
Return to Ethics in the Science Classroom: An Instructional Guide for Secondary School Science Teachers