High School Biology-Chemistry SMILE Meeting
25 September 2001
Notes Prepared by Porter Johnson

Biology/Chemistry

Lee Slick (Morgan Park)
Lee started up a rebus, actually a series of them, each being an element:  Sodium, Carbon, etc.  By the way, a rebus is a set of pictographs, symbols, and operations to represent a word or phrase.  For example

"picture of needle and thread" + D + "picture of a pack of gum" - G =  SODIUM

Get it?? A terrific way to engage kids as they learn about the chemical elements.

Chris Etapa (Gunsaulus School)
Chris began by outlining a presentation to emphasize the importance of  laboratory safety.  In her class she took a raw egg and put it into a petri dish placed on the overhead projector.  Then, she added 2 drops of dilute Hydrochloric Acid [HCl].  As the protein "denatures" it looked dark on the screen.  This graphically illustrates the need to wear safety glasses, since our eyes contain the same types of protein as egg proteins, with the same sensitivity to acids.

Next she presented two mini-labs, which are used to get kids into a "science fair" mode.

  1. Observations on a penny
    We answered a series of questions about a penny from memory only.  Then she repeated the questions while we were looking at the penny.  She had us clean the penny by dipping it into vinegar for a few seconds, coating it with salt, and then rubbing it, so that we could see detail on the coin much better.  This cleaning procedure works very well!  We compared our observations with the answers given from memory, to learn about memories as well as our observational skills.

  2. Testing a hypothesis
    Chris lit an ordinary candle.  She asked us to hypothesize whether the candle burns because of (a) a special chemical in the candle or (b) the air in the room.  She covered the candle with a translucent container, and we saw the flame slowly go out.  Because the candle appears the same as before we covered it, the experiment suggests (but does not prove) hypothesis (b).  Note:  Oxygen O2 in air is necessary for combustion.

Pat Riley (Lincoln Park HS)
Pat asked us how we might make a reaction --- such as dissolving sugar in water --- go faster.  Suggestions included the following:

heating, stirring, breaking sugar into smaller pieces

As to the effect of breaking sugar into smaller pieces, we suggested a refinement, since the surface area was increased and  the particle size was decreased.  [In this sense the "particle size" refer to the size of individual sugar molecules]. Which of these effects is more important?  She considered these two balls of the same size:

The Styrofoam™ ball has more surface area and should have more "sticking power".  Similarly, the increase in surface area, although it does not change the size of each sugar molecule, is the key parameter for speeding the reaction rate.

Therese Donatello (St Edwards School)
Therese presented the following three exercises.

  1. She simulated rock layers in the earth's crust using layers of paper, showing how they are deformed and changed under stress [force per unit area]. She took three sheets of construction paper (rectangles of size about  5 ´ 10 inches; or 12 ´ 25 cm), each of a different color, and made slight 1 inch or 2 cm cuts across the two long sides of each sheet at the same place. She held the stacks of paper by the short sides with both hands, and pushed [either equally or unequally] with her hands to show how the layers were deformed.

    Then she pulled on the papers, the cuts making it easier for the paper to start tearing.  We investigated finding how to tear the paper most easily; that is, was it better to pull slowly, quickly, from the sides, from opposite ends, etc.  If the tearing is uneven and not the same for each layer, it may be because of the different compositions of paper in the various layers.  This illustrates how movements in the earth's crust can lead to earthquakes.  Very nice, Therese!

  2. Each group received one large and one small paper clip.  We looked at the paper clips "edge on"; they were originally flat.  Then we repeated this observation after clipping on 2, 5, 20, and 50 pieces of paper.  As the paper stacks got larger, we could see that the paper clips got progressively more deformed, and their appearances changed as viewed edge on; they were no longer flat.

    The paper clips were made of different materials, such as metal or plastic. We noted that the smaller clips bent more than the larger ones, and even with clips of the same size there was variation in bending because of the different material composition. Also, with smaller stacks of paper the clips stretched, but rebounded when the paper was removed. By contrast, with sufficiently large stacks of paper the paper clips would stay deformed after the paper was removed. Evidently, the clips had reached their elastic limit, and their shape was irreversibly altered.

  3. Therese next passed out balloons and rubber bands, and we measured their relaxed length with rulers.  We then stretched the balloon / rubber band to 1.5 times its relaxed length, let it go, and re-measured its new relaxed length.  We continued the process, stretching by 2 times its original length, 2.5 times its original length, etc.  Here are the measurements for one of the balloons:
    Stretch Factor Measured Length
    1 ´ 9.5 cm
    1.5 ´ 9.5 cm
    2.0 ´ 9.5 cm
    2.5 ´ 9.5 cm
    3 ´ 9.5 cm
    Elastic Limit
    4 ´ 9.7 cm
    5 ´ 10.0 cm
    Note that the elastic limit is reached at somewhere between 3 and 4 times the original relaxed length of the balloon. The rubber band was somewhat more elastic, or more resistant to permanent deformation, than the balloon. The distinct behavior of different materials, or different arrangements configurations of similar materials, is interesting and significant.
Therese led a discussion about the behavior of "real rocks" in the earth's crust, introducing the relevant vocabulary used by geologists.

Notes taken by Ben Stark