Announcement

Rolling Meadows High School (District 214) is actively looking for a chemistry teacher for the 2002-2003 school year.  Responsibilities will include 1 AP Chemistry Class and 3 additional classes of chemistry or physical science.  Rolling Meadows has an eight-block AB schedule.  Classes meet for 90 minutes every other day, except for AP Chemistry, which meets every day for 90 minutes.  Interested parties should contact Susan Illingworth at (847) 718-5724.

Karlene Joseph (Lane Tech HS): Eggs and Diffusion
Karlene put some raw eggs in a container and covered them with vinegar (H⁺) for about 4 days.  The shells (Ca CO₃) dissolved, and we were left with "rubbery  eggs"; ie, the raw egg surfaces were covered by remaining membranes.  At first Karlene had observed bubbles, as a result of the chemical reactions

Ca CO₃ + 2H⁺ ® Ca⁺⁺ + H₂CO₃ 

H₂ CO₃ ® H₂O + CO₂

She weighed a "de-shelled" egg and found that its mass to be 85 grams. Then she placed it  in a sugar solution (Karo® Syrup). After about 40 minutes we poured off the syrup, rinsed off the excess syrup, and  weighed the egg again, obtaining a mass of 77 grams.  Although the membranes on the egg were still intact, water had diffused out through the surface membrane, leaving the egg and mixing into the syrup, which had become more fluid.  [The syrup had lower osmotic pressure (for the solute, water) than the egg,  providing an osmotic pressure gradient, so that water would undergo diffusion, crossing through the semi-permeable  membrane out of the egg and into the syrup.]  An excellent exercise illustrating the effect of osmosis, Karlene! 

Web References:

• Stupid Egg Tricks: http://www.bizarrelabs.com/egg.htm
  
• From Egg to Chick: Where's the Shell: http://www.howstuffworks.com/question231.htm.

Pat Riley (Lincoln Park HS, Chemistry): Kitchen Chemistry & Practicing Observations
Pat divided us into three groups, and each group got one of three liquids:

I: water; II: vinegar; III: dilute solution of  KI (potassium iodide) in water

 The groups got the following four solids in separate bottles:

Each group also received five unknown mixtures of the solids A - D, which were labeled as 1, 2, 3, 4, 5. Three of them were mixtures of 2 unknown solids, and two were mixtures of 3 unknown solids. We observed which solids dissolved in each of the three liquids, looking first at the "known solids" A - D, and then at the "unknown" mixtures. We determined whether, and to what extent, the visual observations of the "pure substances" would permit determination of "ingredients present in mixtures" for each case 1-5. Little sticks were used as spatulas; samples of solids about the size of a grain of rice were taken for each test. Pat supplied 96-well plastic plates for each test, which greatly simplified the process.

Relevant Points:
• Sticks were used to stir each sample.
• For each sample, we added solid to a well, added liquid, and then stirred the mixture with a stick to try to dissolve the solid.
• In all, there were 4 ´ 3 + 5 ´ 3 = 27 samples.
• We observed the following parameters:
  1. Dissolution (or not)?
  2. Color or color change after mixing?
  3. Released bubbles (gas)?
• Since the mixtures 1 - 5 looked like white powder to the unaided eye, their behavior when added to a liquid was an essential component in our analysis.

We presented the findings in the following data sheet:

Pat did two more short activities:

1. She showed a test to determine whether certain solid substances are ionic or not. She dissolved various solids in water, and checked their electrical conductivity using conductivity testers. Ionic solutions are good conductors of electricity!
2. She used the four solids AA - DD [which were not the same as solids A-D of the first activity], putting samples as 4 spots on a glass slide, which she put on a hot plate. As the hot plate became warm, the touched the bulb of a chemical thermometer [that went up to a temperature of 110 °C] to the glass slide, providing a measurement of real temperature in real time. As each change of state (eg, melting) occurred, the temperature was recorded. This is one way of measuring melting points of various solids, as a means of distinguishing them.

We had a really excellent session for our last meeting of the year. See you next year!

Notes taken by Ben Stark