Summer Research Program for Science Teachers

Valentine O. Edobor-Osula, Jr.

Developing a theory about the nature of the contents of a sealed box

INTRODUCTION: Chemistry deals with the changes that matter undergoes. Since the changes are on a molecular level, we cannot observe how they occur. What we usually observe are the difference between the properties of the initial matter (reactants) and the properties of the final matter (products). In the laboratory, experiments are conducted in which the initial and final properties of matter are studied. The chemist attempts to develop a model to explain his or her observations of the changes that take place. [Content Standard Unifying Concepts- Evidence, models, and explanation]

A sealed box containing one or more unknown solid objects will serve as our model of a closed chemical system. A system represents any specific portion material that we are interested in. The system may be isolated (neither energy nor matter can enter or leave). The box is manipulated (shaken, tilted, etc.), and the movements produced inside are recorded. Conclusions are drawn about each observation. Then all the conclusions are combined into a model about the nature of the unknown objects. It is not important that the object or objects be correctly identified. What is important is that the theory can account for all the observations that were made.

EQUIPMENT:

cardboard box (shoe box)

unknown objects

ruler

platform balance

magnet.

PROCEDURE AND OBSERVATION:

Examine the unsealed box assigned to you. Determine its dimensions to the nearest centimeter. Weigh the box to the nearest 0.1 gram. Write your name on the box and give it to your teacher. When you receive the sealed box, weigh it to the nearest 0.1 gram.

TABULATION OF RESULTS:

1. Length of box = ____________ cm.

2. Width of box = ____________ cm.

3. Height of box = ____________ cm.

4. Weight of unsealed box = ____________ g.

5. Weight of sealed box = ____________ g.

6. Difference in weight = (5) -(4) = ____________ g.

7. Is there something inside the sealed box? Shake it gently. What do you hear? _______________________________________________________________________________________________________________________________________________________________________________________________________________

8. What do the sounds inside the box suggest about the nature of the contents? _______________________________________________________________________________________________________________________________________________________________________________________________________________

9. Gently tilt the box so that the contents slide. What do you hear? __________________________________________________________________________________________________________________________________________

10. Hold a magnet against the box and note its effect upon the contents. _____________________________________________________________________________________________________________________________________________________________________________________________________________

11. Compile a list of other ways that the box can be handled to produce motion inside. Compare your ideas with those of the class. _______________________________________________________________________________________________________________________________________________________________________________________________________________

12. For each additional manipulation of the box, listen carefully to the sound inside. Try to feel the object by pressing gently on the underside of the box. Try to draw conclusions about the shape of the object. Record your results in the following table: [5-8 Content Standard A- Use evidence to describe and explain]

OPERATION:

(MANIPULATION) EVIDENCE OF CHANGE CONCLUSION

CONCLUSION AND REVIEW QUESTION:

1. What do you think your unknown looks like? State your reasons.

2. A student performed the sealed box experiment and came to the following conclusions: "My unknown is green and rectangle in shape. It is 15 cm long, 1.25 cm wide, and is flat. It has rounded ends and weighs about 10 g. There seem to be bristles at one end. No odor is apparent.

I think my unknown is a toothbrush. Evaluate his conclusion.

3. The sealed box is supposed to represent a chemical system. After this experiment

has been performed, do you think a student should be told what his unknown

was? Explain_________________________________________________________

____________________________________________________________________

_____________________________________________________________________

[Teaching Standard B- Orchestrate scientific discourse]