Super Ball

Engaging in Exploration, Part 1 Super Ball!

Begin by creating a plain gelatin sample for comparison.

1) Mix the gelatin and hot water (5 ml each as in the first exploration)

2) Pour out the composite on an aluminum foil “mold” as shown at right.  This will make the size and shape of each composite the same.

3) Allow  a few minutes to gel and then hang the test composite on the close line.

This will be the sample from which comparisons of other composites can be made. For example, is the composite stickier, stronger, more rubbery, etc, that the original.  We can truly see the action of the additive on the composite with this comparison.

While the control is dried,  create the first composite:

1) Mix the gelatin and hot water (5 ml each as in the first exploration)

2) Add  2.5 ml Borax to the mixture and stir well.

3) Pour out the composite on an aluminum foil “mold”.

4) Allow  a few minutes to gel and then hang the test composite on the close line.

Facilitating the Exploration: Part 1, Super Ball!

Allow students some time to examine each of the samples and do a quick comparison.  It would be appropriate to set these aside for a time and reconvene class.

With material set aside, ask students how the material compared.  How might we be more precise in comparing the qualities of these two samples?  Suggest that chemists and chemical engineers use tests on materials as a way to make accurate comparisons.  Give students the following array of tests by modeling how each is conducted: 

Notes:  A “control” is a concept we use in science experimentation as a way to compare any changes with a known.  For example, if we want to test fertilizers effect on the growth of a tomato plant we should have at least two plants, one which we put the fertilizer on (the experimental plant) and one we leave alone (the control).  We should otherwise treat the plants in exactly the same way:  the same amount of water, the same sunlight, pot, soil, etc.   In this experiment we need a control gelatin polymer to see how it compares to our composites.

Science Concepts: Borax provides borate ions to cross-link the gelatin polymer chains.  Citric acid (and other acidic compounds) do not provide cross-links but instead, break the polymer chains.  The resulting citric acid/gelatin composite will be runny and slow to solidify, if it solidifies at all.   At this point, share the polymer mini lesson.  End the mini lesson with the visual polymer example of a paper clip chain, making borax cross-links and simulating acids breaking polymer chains.