High School Biology-Chemistry SMILE Meeting
01 May 2001
Notes Prepared by Porter Johnson

Shirley Cesair (Henderson School) Handout: The Peanut Wizard; Electrical Charges
described an activity in which kindergarten students put 8 peanuts inside a plastic "baggy" for an exercise in math / counting.  We examined the peanuts, and developed a description of them.

Shirley then led an exercise in which she blew up a balloon and rubbed it against felt.  Then, she put the balloon over small pieces of paper, which became attached (stuck) to the balloon because of the static charge produced on the balloon by rubbing.  She repeated the same thing with granulated sugar, which also became attached to the balloon, for the same reason.  Interesting!

Sarah Brennan (Robeson HS)  Handout:  Properties Common to all Gases
Sarah gave 35 cc syringes and balloons to each of us.

• Gases have mass:  We used 2 balloons, one inflated with air and tied them with string to form each side of a balance.  From the fact that that balance tilted toward the inflated balloon, we concluded that the inflated balloon has more mass, because of the air inside.  Question:  But does this really prove anything, because of the effect of buoyancy?
• It is easy to compress a gas:  We took a syringe with plunger and stopper, removed  the plunger, and placed the stopper on the small end of the syringe.  We pushed the plunger back into the syringe, and compressed the air inside quite easily.
• Gases fill their containers completely:  We simply blew up a balloon to illustrate this point.
• Different gases can move through each other rapidly (diffusion):  Sarah described spraying perfume through an atomizer in one part of the room, and the students raising their hands when they smelled  it.  Those who were closer to the spray would smell it first, etc.
• Gases exert pressure.  We squeezed an inflated balloon, and could feel the pressure exerted by it.
• The pressure of a gas depends on its temperature: (thought-experiment suggested by Pat Riley)  Submerge the balloon in hot water, and then put it into an ice bath.  You could actually see the balloon expanding and contracting.
Very interesting, Sarah!

Karlene Joseph (Lane Tech HS) Handout: Radioactive Decay
The half-life of a radioactive element is defined as the time required for half of the atoms in question to decay.  For example, the unstable isotope Carbon 14 decays into the stable isotope Carbon 12 with a half-life of 5500 years.  [This feature is used for "carbon dating" of wood and wood products, since the fraction of Carbon 14 in the earth's atmosphere is being kept roughly constant by background cosmic rays.]  We modeled radioactive decay using red licorice [unstable, radioactive] and black licorice [stable], made by Twizzlers™.  We took a full piece of the red licorice, and cut another one successively in halves, which we glued to the paper to indicate the number of atoms present after various half-lives.  The graph looked something like this:

```        Number Left
|
|
|
|
|     |
|     |
|     |     |
|_____|_____|_____|_____.

0     1     2     3     4

Time:  Half-lives
```
We cut the black licorice into pieces to fill in the rest of the column, indicating the number of the new atoms created.
```     |: Number Left       X: Number New
|     X     X     X     X
|     X     X     X     X
|     X     X     X     X
|     X     X     X     X
|     |     X     X     X
|     |     X     X     X
|     |     |     X     X
|_____|_____|_____|_____X

0     1     2     3     4

Time:  Half-lives
```
Good, Karlene!

Notes taken by Ben Stark