BOX 3-6 Sample 2: STEPHANIE

Describe your first experiment:

P.R. + B.S. → cold

What happened?

P.R. + B.S. stayed cold. Changed hot pink.

What can you conclude?

This mixture has nothing to do with the production of heat.

Describe your second experiment:

C.C. + H2O → hot

What happened?

The C.C. + H2O became hot.

What can you conclude?

This mixture provided the heat.

What do you think causes the heat?

The C.C. and H2O make heat for sure. It's possible that the P.R. when mixed with C.C. would cause heat, but we know that P.R. is not really a heat maker all by itself or without C.C. because of the first experiment we did. And P.R. is really a solution with water so that's another reason why water is probably what's needed, along with C.C. to make heat. We'd have to try mixing P.R. with C.C. to see if that gets hot. I think it would, but I still think that just means that water or a liquid like water is needed with C.C. to make heat.

Areas for Additional Practice

√ designing controlled experiments

√ using scientific notation to record experiments and results

Stephanie first decides to omit the calcium chloride and combine phenol red and baking soda. When the reaction's results are cold, she correctly concludes that this mixture has nothing to do with the production of heat. However, she does not control variables in her next experiment, when she combines calcium chloride and water. Her decision is based on the following logical, though faulty reasoning: If phenol red and baking soda do not produce heat, perhaps the other two reactants will! Technically, she should conduct another experiment so all variables are controlled. However, she considers this in her final conclusion when she discusses the possibility that mixing phenol red and calcium chloride (which she didn't try) would result in heat. She speculates on the results of this reaction, and goes on to share reasoning for her ultimate conclusion—that water, or a liquid like water, is needed with calcium chloride to make heat. Given the limitation of the two experiments, the combination she first chose, and the fact that she is aware of the weakness of her experimental design, hers is a good handling of the results. She implies that she would explore the unanswered questions if given an opportunity to conduct a third experiment. Like Jonathan, Stephanie uses chemical notation of some of her own abbreviations.

SOURCE: Barber et al. (1995).

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