High School SMILE Meeting
13 February 2001
Notes Prepared by Porter Johnson

Glenda Ellis (Williams School)
Handout: Layers in a Glass

Glenda explored the concept of density (lower density liquids float on those of higher density) using oil, isopropyl (or rubbing) alcohol, and water, using food coloring to distinguish the liquids, so that their layers could be seen more easily.  Before doing the experiment, we made guesses as to which of the liquids would be least dense, most dense, and intermediate in density.  She put food coloring only in water and alcohol, since the water-based food coloring would not dissolve in oil.

The material first formed three layers from bottom to top, corresponding to water, oil, and alcohol, in decreasing order of density.  After mixing and settling, there were only two layers, rather than 3, since the alcohol and water mixed in each other, and the color was a "mixture" of those for alcohol and water.  The oil layer, which still did not mix with the other two, went to the top.

For additional information, check the website http://library.thinkquest.org/2690/exper/exp25.htm.

Erma Lee (Williams School)
Estimation

Erma had three containers, each containing a different kind of dried beans [or peas]; the sizes were "small", "regular", and "large".

• We took a spoonful of each kind, and put them into separate compartments of a Styrofoam™ food tray, and we put an orange into the fourth compartment.
• We peeled the orange, saving the peelings, and separated one section from the orange.
• We then quickly estimated the number of each kind of bean that was on our plates., as well as the number of sections left on the orange, from which we had just removed a segment, and the number of pieces of orange peel.
• The estimates were then collected.
• Next we put the section back into the orange, and re-covered the top half of the orange with pieces of peeling.  Then, we estimated how many pieces of orange peel were required for this.
• Then, we removed this segment again, and estimated the number of seeds inside the segment.
• Next, we bit the orange, and estimated how much was left.
• Then, we counted and recovered the number of beans, the number of orange sections, and the number of pieces of orange peeling.
• We compared and recorded our estimates of the number of each type of bean, and the total numbers.
• We traced our hand on a sheet of paper, and on a second sheet we traced our foot.
• For one of the three types of beans, we estimated how many (placed end-to-end) would be needed to go around the tracing.  Then, we covered the perimeter with beans, and compared our estimates with the actual numbers.

At some point in the experiment we ran out of beans. [Be sure to get a plentiful supply when you do this experiment.]

Pat Riley (Lincoln Park HS) Conservation of Mass in Chemical Reactions
used a large 2-pan balance.

• On one pan she put a small (about 200 ml) bottle of Hydrochloric Acid (HCl), and a bottle partially filled with Zinc metal (Zn).  On the other pan she put two empty bottles of the same size, and added small plastic chips to increase the mass on that side to obtain a balance.
• Then she poured the Zn into the HCl, and put in the stopper.  A chemical reaction was seen to occur, but the balance remained in equilibrium, so that no mass was "lost' in the reaction.  A bit of hydrogen gas (H2) escaped when the stopper on the reaction bottle popped out, but this did not materially affect the beam balance.
• Pat correlated the phenomenological demonstration of conservation of mass with the balanced equation
2 HCl  +  Zn  ®  ZnCl2  +  H2
• Pat repeated the experiment with Magnesium metal (Mg) in HCl:
2 HCl  +  Mg ®  MgCl2  +  H2
Notes taken by Ben Stark.