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JOHN H. WOODBURN. PhD 9208 Le Vslle Drive Chew Chase. Maryland 20015
Another Look at Our Teaching Methods Should we pay more attention to the everyday mechanics of teaching chemistry? Are there things we can do to help students get more out of our lectures, demonstrations, lab exercises, films, and other instructional formats?To look into these questions, this column is being "test-marketed."
Pros and Cons of the Silent Demonstration The following example of this format might he used to introduce the concept of solubility product and lead up to the question: When do precipitates form? The format assumes that the students enter the classroom and the instructor hegins the demonstration with a hare minimum of "sound track." Step. 1. Prepare half liter quantitiesof0.1 Msolutions of lead nitrate and potassium iodide. Step. 2. Combine 200-ml portions of these two solutions. Step. 3. Dilute 20-ml portions of the two solutions to 0.01 M and then combine these two solutions. Step. 4. Shake thoroughly the combined solutions f r o m S p 2 and transfer a 50-ml portion of the suspension to a 500-ml flask. Add 450 ml of water with constant shaking. Step 5. Offerto carry out any additional procedures requested by the students. "Coax" the suggestion to dilute only one of the two0.1 M solutions before combining them. Step 6. Offer to answer any questions dealing with procedures, adding- oerhaos to imorove observations. However. insist . . suaaestions -on postponing all questions or comments involving explanations of anv of the observations. Step 7. To encourage each student to become involved in the demonstration, postpone further discussion until each student has turned in a written answer to such a question as: When do precipitates form? To provide an evaluation of the effectiveness of this "silent demonstration'' fnmlnt, srwral groups of students were asked to civr rensons why their oeiahhm mnv have failed to ohtinn theinformation needed to a
