High School Biology-Chemistry SMILE Meeting
06 April 2004
Notes Prepared by Porter Johnson

Jane Shields  [Calumet HSl]         Chemical Indicators, Homemade Litmus Paper, Acids & Bases
passed around a sheet of instructions on making your own pH Indicator from red cabbage juice [Water What IFs -- pH Indicators: http://www.ncsu.edu/sciencejunction/depot/experiments/water/lessons/pH/pHindicator.html]. Jane showed us some litmus paper that she had made by soaking filter paper discs (about 80 mm in diameter) in Petri plates containing red cabbage juice, drawing off the excess liquid, and letting them dry in air.  When drops of different liquids were placed on the indicator paper, the following color changes were produced:  acids -- pink; bases -- green.  Unfortunately, this was a demo only, so that we didn't get to make our own sheets.

To prepare cabbage juice, slice a purple cabbage into slices, and cut into small pieces with ribbon shears.  Simmer the cabbage in water for 30 minutes.  Then strain the mixture to separate the purple cabbage juice from the remaining insoluble fiber.  The juice is usually quite purple at this stage.  [Distilled water may be necessary, if local water supply is too basic, for whatever reason.  However, most classmates who have done this report that there are no problems in using tap water.]  Ken Schug mentioned that adding baking power to the juice produces a pH near 7 --- a neutral solution.

Colorful Chemistry.  Wonderful, Jane!

Ben Stark  [IIT Biology]         The Can Crusher
brought in a supply of Aluminum pop cans.  He added water to a can to a depth of about 1 cm, placed the can on a hot plate, and turned on the heat.  He waited until the can was filled with steam, but with some of the liquid water still present.  It took about 10 minutes to reach this stage with his setup.  He then grasped the can with tongs, and quickly inserted the inverted can into a large container of cold (even ice) water.  Pow! The can imploded. Why?

Explanation:  As liquid water in the can is heated, some of it turns into steam, which pushes air out of the can.  The (steam +air) inside the can is equal to the atmospheric pressure outside the can --- about 14.7 pounds per square inch or 105 Pascals (Newtons per square meter). When the inverted mouth of the can is put into the large bath of water, the trapped steam in the can cools and rapidly condenses.  Thus, the total pressure inside the can becomes less than atmospheric pressure outside the can, and the outside pressure crushes the can.  The can is not strong enough to withstand the force of the pressure difference.  It takes very little time for steam inside the can to condense rapidly into liquid water, and for the pressure inside the can to decrease.  Why doesn't water rush into the can?

This experiment also works very well with an old rectangular can (gallon -- 4 liter) that once contained ditto fluid, etc, and which has a screw top.  After heating it to form steam (as with the pop can), we carefully and tightly screw the cap on, and remove the can from the hot plate.  As the can cools, it will gradually collapse in a series of sudden deformations.

Good show, Ben!

Terry Donatello [ST Edwards: Elmwood Park]         Identification and Chemical Properties of Minerals
showed us how to use 3D "Viewmaster" Glasses to view paired stereoptic pictures of crystals. She also had molecular models for various crystal structures.  We compared the pictures of the crystals to the models that Terry's students had made with wooden sticks, toothpicks, twist ties, pipe cleaners, and wire. The key parameters included the number of axes, their relative lengths, and the angles between them.

We also looked at stereo pictures of various biological macromolecules (proteins) that were in a Biochemistry textbook.  Terry then  passed out several baggies containing small pieces of minerals (about 2 cm in size).  We ran the following tests in our attempts to identify them. 

Finally, Terry revealed the identities of the various minerals.  

For a set of crystal images from Alan Guisewite's Mineral Collection see the website http://www-2.cs.cmu.edu/~adg/adg-piimages.html .

Sherlock Holmes, Super Chemist! Very good, Terry!

Notes taken by Benjamin Stark and Pat Riley.