High School SMILE Meeting
1999-00 -- 05-06 Academic Years
Properties of Materials

07 September 1999: Ken Schug (IIT)
displayed a U-tube filled with a different transparent liquid in each leg of the tube. It looked like it could be a single liquid. Because of their density difference, the liquid levels were different. But the interesting thing was that Ken had showed this to us 6 months ago! During all that time, the diffusion of one liquid into the other was so slow that they had not yet mixed into a single fluid with a common density, and so still showed different levels! Diffusion takes a long time!

26 October 1999: Erma Lee (Williams School)
started with several identical jars (nearly pint size), one filled with marbles. (handout) She filled it with water, and asked us to guess how much of the space was filled with marbles, and how much with water? Guesses ranged from 1/3 to 2/3, and then Erma poured the water out of the marble jar into an empty one, which became about half-filled. Ahah! About half the space in the marble jar had been filled with water, the other half with marbles! Neat! But then Erma did the same thing with sand! She filled a jar with dry sand, and asked the same questions. This led to much fascinating discussion, and then Erma gradually added water from a full jar to the sand jar. The sand at the top grew darker as the water soaked down into the sand and made it wet. And fine bubbles began to come up to the top surface of the water at the top of the jar. Air! Erma asked, "If a straw were to be stuck down into the jar where the sand is still dry, could air be sucked out to more rapidly fill the jar with water?" No one volunteered to try it, however. Now - how much water could we add to the sand-filled jar? More fascinating argument and discussion! Do you know the answer? Have fun!

09 November 1999: Melinda Ross (Hefferan School)
asked us to define gravity, and siphoning (handouts). We decided that gravity produced an attraction between objects with mass. And siphoning is the movement of liquid from a higher to a lower level through a tube which goes higher than the upper level. Then she gave us each two cups and a flexible straw and water, and we made our own siphons. They worked! Neat! Will a siphon work in a vacuum? Discussion showed we disagreed on the answer. What do YOU think?

07 December 1999: Marva Anyanwu (Green School)
got us involved in a discussion of physical vs chemical changes. Several definitions were suggested, and we got to the idea of formation of a new substance. We then formed into groups and Marva gave us a handout. "Chemical Change." Then, using a self-locking, re-sealable plastic bag, we placed various chemicals in. the bag and made observations. With citric acid (powder) baking soda (powder) and a smaller sealed bag with cabbage juice placed in the bag, nothing happened. But when we caused the smaller bag to open, mixing the cabbage juice with the two powders, a gas was produced with red foam and it got cold. We also noticed multiple "starburst" patterns on the side of the bag that had no label. The same patterns appeared on the outside of the smaller (cabbage juice) bag within. No explanation for this developed. A mystery!

Editorial comment: It is possible that in the manufacture of the plastic bag, an electrostatic charge is embedded, and the powder could be attracted to stick to that charged plastic.

01 February 2000: Zoris Soderberg (Webster School)  
began with a hard boiled egg and a narrow-neck bottle. How to get the egg inside? Drop a small chunk of burning paper into the bottle, place the egg in the neck, and when the heated air in the bottle cools, air pressure inside becomes less than atmospheric pressure outside, forcing the egg into the bottle! Discussion pointed out that atmospheric pressure changes force the air to move from high to low pressure regions - producing wind - and weather!

Next, Zoris set a paper cylinder (made from a tea bag) on one end on the table and lighted the top end. When the flame reached the bottom, the ash remaining rose up 4 - 5 feet into the air! The rising column of hot air (convection current) - produced by the heat from the flame - carried the ash upward. An example of air motion (wind) produced by temperature differences (local heating).

Finally, Zoris showed us a capped plastic pop bottle containing water, oil, and some beads. The water was colored with a dye. When she tipped the bottle, one could see the swirling motions of water and oil, carrying beads along. A "poor man's Lava Lamp" - and showing fluid motions and turbulence - not unlike fluid motions of the atmosphere. A nice set of experiments to show us some atmospheric/weather science!

15 February 2000: Zoris Soderberg (Webster School)
filled a jar with hot water and placed a tea bag on top. After a time several layers of different colors developed, which was likened to layers of air in the atmosphere. It was hypothesized that density increased as tea ingredients dissolved, and then that layer would sink. Ken Schug suggests that an increase in density might occur due to the tea bag decreasing the temperature of surface water, and leading to the sinking layer. Ahah! A good subject for further investigation!

Zoris rubbed a polystyrene cup on her hand, and the cup stuck to it! Why? Static electricity! Opposite charges attract.

Finally, Zoris placed some weak tea in a clear plastic cup, and had a volunteer hold an index card over the top of the cup. Then she had the volunteer invert cup-with-card and remove the hand from holding the card against the cup. Behold! The card stayed in place and so did the water inside the cup! It didn't fall out! Explanation? Air pressure outside the cup exerts greater force up on the card than the pressure of liquid and air inside exerts a force down. Thanks, Zoris!

12 September 2000: Erma Lee (Williams School)
turned us into bean counters! She gave us dried, red beans and asked us to estimate how many beans it takes to go around a person's shoe. Then we had to measure it! Erma asked us to trace an outline of our shoe on an 8.5 in  x 11 in paper, and then we did the measurement on the tracings, laying the beans end-to-end. The distance around was measured in "bean lengths." She asked us to measure the surface area within the tracing, a sort of surface area of a shoe. To do this we placed as many beans as possible within the outline and in a single layer, and counted them. We repeated these measurements for our hands using the same techniques. We found that the surface area of our hands was about 75% that for feet, and the perimeter of a hand fingers closed) was about 80% that for feet. What a rich learning experience! - involving measurement, observation, comparison and conclusions. Thanks, Erma!

26 September 2000: Pam Moy (Morgan Park HS),
in an Introduction to Data Gathering, had us busy using metric tape measures to find the height, length and width of the desk at the front of the room. All measurements were taken in cm, except that the length of the table in front was measured in meters. Then we all measured the length of our feet in cm and mm, the height of each of our lab partners in m, and the length of the hallway in meters. We also found the temperature of water in two beakers, one beaker filled with hot water from the coffee pot, the other at room temperature. We found that one "lap" around the hall of our Life Sciences building is approx. 131 meters (approx. 16 m wide x 50 m long). A great many details had to be settled about how to make the many measurements, and much discussion arose. Made us think! Good stuff, Pam. Thanks!

10 October 2000: Chris Etapa (Gunsaulus Academy)
continued on the theme that "things aren't always what they seem". She poured tonic water into beakers. The beakers were placed on white paper and the room was darkened. When she shined white light into a beaker, we saw only white light color. But with UV light we saw a lavender/blue color. It turns out that the quinine in the tonic water absorbs UV light and fluoresces, producing the lavender/blue color. It was somewhat difficult to be sure that the color wasn't coming from the UV light alone. The experiment works best in a very dark room. What a fascinating way to provoke student interest! For more information see http://en.wikipedia.org/wiki/Quinine.

10 October 2000: Karlene Joseph (Lane Tech HS)
borrowed from the following book

Science Is ...: A source book of fascinating facts, projects, and activities.
Susan V Bosak [Firefly Books 2000 $29.95 List Price]
ISBN 0 - 5907 - 40789
She filled a glass right up to its rim with water. Then she asked the question:
"How many paper clips do you think we can add before water will run over the rim?"

Our estimates ran from 24 to 100. So ... we added paper clips to find the answer. By the time we got to 100, we were all astonished. But then we added still more - and got to 188 clips. The water was bulging over the rim, but it did not spill! Surface tension of the water was the phenomenon illustrated; the water behaved as if its surface was a thin, elastic film, keeping the bulk of the water from spilling over. Next, with a beaker containing water, Karlene used a tweezers to lay a needle gently on the surface of the water, where it floated! Surface tension, again! 

Then she added a drop of detergent (dishwashing fluid) to the water, and the needle dropped to the bottom of the beaker. The detergent had practically destroyed the surface tension so the needle was no longer supported by the surface tension "elastic film!" "Let's try it on the water bulging over the rim in the glass with paper clips!" we suggested. So Karlene carefully added a drop of detergent, and sure enough! - the surface tension "film" disappeared, and the water spilled out over the sides of the glass! Finally, Karlene floated a match on the surface of water in a beaker. Then she added a drop of detergent on one side of the match. The match was expected to move to one side as surface tension on that side was reduced, but we weren't sure we could see significant movement. Why didn't this work? But what a fascinating set of experiments to show the reality of surface tension!

13 February 2001: 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.

13 March 2001: Mary Scott (Williams School) The Great Pepper Chase
In this activity we investigated surface tension. We took an aluminum pie pan half full of water, and added small amounts of these ingredients in succession:

Then, we started over using these ingredients in order:

We concluded that soap reduced the surface tension of water, causing the floating pepper / cinnamon to go to the rim, whereas sugar increased it, causing them to go back toward the center.  We repeated the experiment with varying amounts of the ingredients, to study the effect.

13 March 2001: Karlene Joseph (Lane Tech HS) Two Liter Bottle Tornado Makers
told a story about the two connected two-liter bottles [one initially full of water and one initially empty] that have been used in the summer SMILE program for many years to illustrate the action of a tornado. She produced a simple tornado maker on the spur of the moment at a school party using empty pop bottles.  Her students were genuinely impressed with the device, which none of them had ever seen.  She showed us the apparatus in action.  When the apparatus is inverted, the water in the top bottle can be made to stay there because of air pressure in the bottom and surface tension of water in the connecting tube.  Agitation interrupts this quasi-stable situation, and water flows to the bottom bottle, a vortex being set up in the process. 

27 March 2001: Mary Scott (Williams School) The Great Pepper Chase
In this activity we investigated surface tension. We took an aluminum pie pan half full of water, and added small amounts of these ingredients in succession:

Then, we started over using these ingredients in order:

We concluded that soap reduced the surface tension of water, causing the floating pepper / cinnamon to go to the rim, whereas sugar increased it, causing them to go back toward the center.  We repeated the experiment with varying amounts of the ingredients, to study the effect.

27 March 2001: Karlene Joseph (Lane Tech HS) Two Liter Bottle Tornado Makers
told a story about the two connected two-liter bottles [one initially full of water and one initially empty] that have been used in the summer SMILE program for many years to illustrate the action of a tornado. She produced a simple tornado maker on the spur of the moment at a school party using empty pop bottles.  Her students were genuinely impressed with the device, which none of them had ever seen.  She showed us the apparatus in action.  When the apparatus is inverted, the water in the top bottle can be made to stay there because of air pressure in the bottom and surface tension of water in the connecting tube.  Agitation interrupts this quasi-stable situation, and water flows to the bottom bottle, a vortex being set up in the process.

10 April 2001: Karlene Joseph (Lane Tech HS) Propagation of Sound 
when sound travels from one medium to another, the speed and quality of the sound change.  This fact was demonstrated by hitting a metal strip [about 3 cm ´ 30 cm ´ 1 mm] on a string. We first hit the strip with a pen while holding it, and then put the strip itself against our ear. In the latter case the sound is transmitted through the strip, as well as in the air; in the former case we hear it only through the air. The sounds were quite different for the two cases.

01 May 2001: 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!

09 October 2001: Marva Anyanwu (Lincoln Park HS) The Tensile Strength of Spaghetti (handout)
The handout explained that "raw spaghetti" is a surprisingly strong material --- before you cook it.  Spaghetti***  is categorized by thickness of the strands.  In particular, angel hair spaghetti is thin, and "regular spaghetti" is described as #8 on the boxes.

Tensile strength  is measured by stretching an object until it breaks.  A rope used in a tug-of-war is under tensionCompression occurs when forces push into an object. For example, a pillar supporting a building is subject to compression.  When a long, thin object is supported horizontally at its ends and pushed down at the middle, the top edge is under compression and the bottom edge is under tension.
To measure the tensile (tension) strength of a length of spaghetti, you can bend it by adding weight to its center until it breaks.  Support opposite ends of a single piece of spaghetti, allowing 2 cm of each end to rest on the support.  Hold those ends in place so that the spaghetti cannot move.

We worked in groups, using both "thick" and "thin" spaghetti. We placed a spaghetti strand with  the ends on two desks, and over the strand we looped a piece of string that was tied to a Styrofoam™ cup.  We added weights to the cup until the spaghetti strand broke, and recorded the data.  We drew the following conclusions:

Marva mentioned that she was particularly interested in the SMILE Biology-Chemistry class. She hadn't thought of spaghetti as being strong, and was surprised by the experiments.

*** The word spaghetti means little strings in Italian and is always plural. The rumor that spaghetti plants grow in long thin patches between lanes on interstate highways is false. After all, spaghetti requires a hot, dark environment for proper development.

19 March 2002: Ben Stark (IIT Biology) -- Bernoulli Principle
Ben
took a strip of paper, folded it in half, and held it vertically at the crease.  He then blew (X) through the crease:

           Paper held at crease
.
(high P) / \ (high P)
/ \
/ X \
/(low P)\
/ \
(Blow through crease)
We noted that the two halves moved together as he did this. The Bernoulli Principle explains this as well as the flight of birds and airplanes. According the Bernoulli Principle:
  1. A  moving fluid has lower pressure than a stationary fluid.
  2. The faster the movement of the fluid, the lower the pressure in the fluid.
He laid out a cross-section profile of an airplane wing on the floor, about 10 feet long, with a "rounded" leading edge and a "sharp" trailing edge. For streamline flow, and given the shape of the wing, air must move more rapidly above than below, resulting in greater pressure below than above the wing.  (See http://www.eskimo.com/~billb/miscon/wing2.gif.)  To illustrate this point, Barbara Pawela and Karlene Joseph walked along the profile of the wing, starting together at the leading edge and arriving together at the trailing edge. But Karlene's speed (along the top of the wing) was larger than Barbara's (along the bottom of the wing).  Karlene had to walk faster than Barbara to reach the end of the walk at the same time.  At "walking speed" (say, 5 miles per hour), the pressure differential is rather small, but at a take-off speed (say,  150 miles per hour) the pressure differential is large enough to lift the airplane.  Very interesting, Ben, and just how do birds take off?  For additional information on airplane flight, see the NASA webpage Bernoulli versus Newton http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html.

19 March 2002: Ken Schug (IIT Chemistry) -- More on the Bernoulli Principle
Ken
held up a thread spool and a small piece of cardboard (index card) for us to see.  He alternately blew air into and sucked air out through the hole in the spool, so we would understand what he was about to do next. With the spool held vertically, he held the card flat against the bottom of the spool, and centered it on the opening of the hole. When he sucked air through the hole and released the card, it remained stuck on the bottom of the spool. We anticipated that. But then he blew down through the hole and released the card. Surprise! The card remained stuck to the bottom of the spool as long as Ken could blow air through the hole. When he ran out of breath, the card dropped off! How come?  The explanation for this feat is, once again, the Bernoulli Principle. [See http://home.earthlink.net/%7Emmc1919/venturi.html .] He also mentioned that one may reduce air pressure in a flask by connecting it with tubing to the side of a pipe through which there is a fast flow of water.  Because of the lowered water pressure inside the pipe, the pressure at the hole is reduced, and the flask may be partially evacuated.  Very good, Ken, but just how do we learn to fly like the birds?

07 May 2002: Therese Donatello (ST Edwards School, Elmwood Park) -- Porosity revisited
Terry continued the discussion of porosity of materials, which was begun in the 02 April 2002 class by Erma Lee. Whether materials such as soil are composed of rocks or very fine particles, there is always some space between the pieces of solid material.  This empty space, called pore space, is the subject of the investigation. She filled identical vessels with plastic beads of various diameters, and then measured the amount of water required to fill the container.  She determined the porosity, as given by the ratio of the volume of water added to the total volume of the container.  We obtained the following results:

Diameter of Bead         Porosity
12 mm      0.53
7 mm      0.42
4 mm      0.43

Ken Schug pointed out that for large containers, these porosities should all be the same, since the beads have the same spherical shape, and the fraction of empty space should be independent of the bead diameter.  The discrepancy occurs here for the largest beads, because our vessels have a volume of only about 50 ml.  Very absorbing lesson, Terry!

07 May 2002: Marva Anyanwu (Green Elementary school) -- The Secret of the Speeding Boat
Marva illustrated the concepts of surface tension, cohesion [water attracted to water], and adhesion [water attracted to paper] by using paper "boats" floating on water inside plastic boxes. The idea is to cut the boat with a V shape in the back, let it float on the surface of the water in the boxes, and then put one drop of liquid detergent on the water surface behind the boat, right at the apex of the V.  The boat will jet forward. For a similar exercise, see the lesson #1 by John Scavo on Surface Tension, on the SMART Program home page, http://www.iit.edu/~smart/. Neat-o, Marva

07 May 2002: Mary Scott (Williams School) -- Black Magic
Mary led us through an application of paper chromatography to determine the different components of pigmentation in the ink in a black, water-soluble magic marker. First, she cut a closed paper ring from a coffee filter, and made an arc around the upper rim of the ring with the black marker.  Next, She placed that ring   into a clear plastic cup containing a little water in its bottom, with the marked arc on  the  paper strip lying above the level of water in the cup.  A few minutes after she left the paper in the cup, the water mark on the coffee filter began to rise because of capillary action.  The component colors in the ink began to separate; she had constructed an "ascending chromatograph".  So, black is colorful as well as beautiful!  For more details, see the Exploratorium Museum website:  http://www.exploratorium.edu/science_explorer/black_magic.html. Thank you, Mary

07 May 2002: Brenda Wall (Williams School, 4th Grade) -- Slick Sliding Soap
Brenda gave a handout of a lesson prepared by Judy Schneider -- with the assistance of science teachers at Chester A Nimitz Middle School -- 
LA Unified School District, which are available on the Science Project of the Week website:  http://spow.org.  The lesson, which involves studying whether soap slides better with hand lotion, water, or cooking oil, is also available on The Lesson Plans Page website:  http://www.lessonplanspage.com/.  The specific location of this lesson is http://www.lessonplanspage.com/ScienceExWhatMakesSoapSlideMO68.htm.  Interesting, Brenda!

08 October 2002: Therese Donatello [St Edwards Middle School]     The Properties and Phases of Matter [http://chemistry.about.com/od/generalchemistry/a/gedreview_4.htm]
Therese
introduced this phenomenological activity by reminding us that the universe is composed of matter and energy, both of which exist in different forms, but cannot be created from "nothing". Thus the "laws" of Conservation of Energy and of Matter, though we know matter and energy can also be inter-converted (E = mc2). She applied these ideas to phase changes --- inter-conversions between the solid, liquid, and gas forms of a pure substance --- which involve energy. This explains why we feel cold when emerging from a shower, because the liquid water uses energy to evaporate as a gas and takes that energy from our skin, thereby lowering its temperature. A handout sheet showed a typical time vs temperature plot for starting with a solid and adding heat until it becomes a gas. Even if heat is being added at a constant rate, the temperature increase is not steady, but contains two plateaus corresponding to the (normal) melting and boiling points where  the added energy causes a phase change with no increase in temperature. Terry distributed sets of three thermometers and small pieces of absorbent cotton. We wrapped the cotton around each thermometer bulb - left one dry, soaked the second one with water, and the third one with rubbing alcohol (dyed green for identification). We then took temperature readings and discovered that the two thermometers with "wet" bulbs gave lower temperatures than the dry one, with the alcohol slightly cooler than the water. At Terry's suggestion we then fanned the thermometers, and found a further decrease in temperature for the two wet bulbs. A typical set of readings was (in the order dry, water, alcohol in degrees Celsius) 24, 20, 19 without fanning and 23, 15, 11 with fanning. Again the cooling is due to the liquid removing heat from its surroundings --- which includes the thermometer bulb  --- to change from a liquid into a gas. A technique based on measuring the difference in temperature between "wet" and "dry" bulb thermometers is the traditional way to determine relative humidity of the atmosphere. Thanks, Terry, for an exciting and educational experience! This also shows us why alcohol rubs are so cooling. [The temperature difference between alcohol and water occurs because the alcohol evaporates faster, even though the energy per gram needed for evaporation is actually larger for water.]

05 November 2002: Carol Giles [Collins HS]      BOBBING MOTHBALLS
Carol
set the stage for her presentation by informing us that we were a "cognitively delayed", 9-12 class in the third week of Earth Science. She called each group to collect and take to their seats the following items: a large (500 or 1000 mL) plastic graduated cylinder all nearly filled, but with varying amounts of water, 3 or 4 moth-balls, and a small packet containing "effervescent tablets" (say, generic Alka-Seltzer®). We all showed we could follow directions by adding one mothball and watched them sink to the bottom. We then dropped in one of the tablets, noticed bubbles of gas "escaping" from them and "oohed " as the mothball rose to the top and hung near the surface. We then added the other mothballs, which soon joined the original one at the surface of the water. After a few minutes the fizzing stopped and the balls dropped to the bottom, only to be reactivated when we added the other tablet. Carol told us to observe closely; when we did, we could see many bubbles of gas adhering to the moth balls at the surface but with only a few bubbles on the mothballs after they sank. We figured out that the gas bubbles made the mothballs "lighter", or, more scientifically, decreased the average density of the moth balls so they became less dense than water and (like a submerged piece of wood) floated to the top. (When the bubbles escape, either by joining the atmosphere or dissolving in the water, they sink.) Carol then passed out sheets containing the procedure, and told us that in her classes students use the back of the handout to write a one page lab report using a standard outline (which she put on the board):  Purpose ... Hypothesis ... Conclusion. Similar phenomena can be observed by adding (fresh) raisins to clear soda pop (often described as sewer lice)  to catch students' attention!  In this case the dissolved carbon dioxide in the soda does the "lifting". The effervescent tablets probably contain sodium bicarbonate (baking soda) and a weak "edible" organic acid which react to form carbon dioxide which is only slightly soluble in water except at high pressure. Thanks, Carol, for good ideas -- and an uplifting experience!

19 November 2002: Erma Lee [Williams Elementary]        The Bouncing Buttons and Raisins
Erma passed around a handout Bouncing Buttons, obtained from Junior Science Experiments on File™, published in  ©Facts On File, Inc. The idea is to mix vinegar (an acid) with baking soda (a base) to produce carbon dioxide (a gas), which appears as bubbles in the glass. These bubbles will attach to objects at the bottom of the glass, and may make them light enough to float, or "bounce" off the bottom.   We tried this  with buttons, and found that some buttons "bounced" better than others.  One can also do the same experiment with raisins. We felt that the differences were due to the following factors:

What do you think?

Very uplifting, Erma!

10 December 2002: Chris Etapa [Gunsaulus Academy]      Measuring Density 
Chris followed up on the pencil gambit that she started at the last class, in which he seemed to demonstrate that the density of the pencil depends upon its orientation --- i.e., whether it is vertical or horizontal. She first floated a pencil on its side on the surface of water in a pan, and then she put the pencil down into a graduated cylinder containing water.  The pencil sank and touched the bottom of the cylinder, ALTHOUGH a good portion of the pencil was still above the water, because the cylinder was shorter than the pencil.  When we substituted a shorter pencil, it floated whether placed horizontally or vertically, so that we were spared the difficulty of having to conjure up some sort of explanation of the effect.  AHA!

Continuing with the density theme, Chris then demonstrated making density bottles by adding a few drops of blue food dye to a vessel containing approximately equal volumes of water and mineral spirits. Mineral spirits are sold at hardware stores as a paint thinner, and probably consist mostly of hydrocarbons (like gasoline) that are not soluble in water.  We saw two layers of fluid --- a clear layer (mineral spirits) on top, and a blue layer (water) on the bottom.  Several of us made our own density bottles.  When the bottles were shaken the layers seemed to mix, but they separated quickly into two separate layers when we stopped shaking the bottle.

Comment by Ken Schug:  Other household oils tend not to work as well, since they emulsify when shaken; that is, they break up into very small droplets that are very slow to come back together.  You can also prolong the separation time by adjusting the densities of the two immiscible liquids to be nearly equal.  He mentioned a system in which the upper layer assumed a hemispherical shape, rather than the usual flat interface surface, and said that when those systems are shaken, it may take many days for separation to re-appear.

Finally, in keeping with the spirit of the season, Chris demonstrated and gave out instructions for making an attractive holiday wreath from plastic sandwich bags [use the cheap ones, and not those with zip-lock tops, which would have to be removed in any case!].  Using a circular wire wreath frame that is readily available at craft stores, she tied the bags around the wire with a single overhand knot, and pushed the bags together tightly until the wreath frame was filled.  [Be sure to use the small wreath frame, since the medium sized frames would require several hundred bags.]  Then, she trimmed the outer ends of the bags with scissors and fluffed the bags.  The wreath can be even decorated with self-stick thingies, if desired.

Good work, Chris!

28 January 2003: Pat Riley [Lincoln Park HS, Chemistry]      How Thick is a Piece of Aluminum Foil??
Pat
had us separate into groups of about 4, and then gave each group the following problem:

Task: Determine the thickness of Aluminum foil!  Write down the steps your team does in order to solve this problem.

Time:  You have 20 minutes to solve the problem

There is more than one way to attack this problem. The following solutions were proposed:
  1. Fold the foil over a number of times [and count how many times!], press the folds flat so that there is no space between them, measure the total thickness, and divide by the number of folds.
  2. Cut a piece of foil, and measure its surface area and its mass M . Then, fold it up, put it in the graduated cylinder partially filled with water, and measure the volume V displaced by  the compressed foil. Now, the density, D, of Aluminum foil of mass M, volume V, area A, and thickness t are related by
    D = M / V = M / ( A t)
    Solve to determine the foil thickness t.
  3. Proceed as in the previous case, but use the density of Aluminum given in the textbook (say, 2.699 g/cm3 at 20° C), which would surely be more accurate than that determined in the rather difficult, imprecise measurement of D in the previous step.
  4. ... and ... Did anybody  who read the label on the foil box  make use of the information given there?  Was this just 3 mil foil, [thickness t = 0.075 cm] or what?

Good work, Pat!

11 March 2003: Barbara Pawela [May School, retired]      Strong Ice:  chbi1700.htm
Barbara
made a presentation based upon a lesson that she developed in SMILE in Summer 2000, which consisted of the following activities:

  1. She placed various canned soft drinks inside Ziploc™ bags, put them in the freezer for several days, and brought them to class.  The cans had failed in various ways, with punch-through at the top, or large deformation.  She did the same experiment with filled glass and plastic bottles.  The glass bottles shattered, whereas the plastic bottles either shattered or were greatly deformed.  We concluded that there is power in the expansion of water when frozen into ice.  She also froze water in a metal can with a lid --- the lid being held in place with pencils and heavy tape.  The pencil didn't break, but it did bend so much that the lid was pushed off.
  2. The second activity involved mixing INSTANTS expandable capsules into a glass half-filled with water, and observing the expansion of the sponge toy as fluid was absorbed into it..
  3. The third activity involved putting a water-filled vial with a tightened screw cap into a salt-ice mixture.  After about 20 minutes the vial cracked, because ice had begun to form inside the vial.
  4. Finally, Barbara placed a Nickel on top of an ice cube, and let it sit for a few minutes.  We found that the Nickel had become stuck to the ice, and had to be pried off.  Why?

Fascinating, Barbara!

09 September 2003: Pat Riley [Lincoln Park HS, chemistry]        Recognizing Physical Properties: Comparing and Contrasting
Pat
began by holding up two 500 ml beakers, one which was 50% filled with a red liquid, and the other 80% filled with a red liquid [red food coloring in water]. She asked us to find as many similarities as possible between to two liquids [same color, same smell, same density, pour the same way --- same viscosity, etc.].  The only difference appeared to be in volumes in the beakers.

Pat then replaced the 80% beaker with one that was 50% filled with a clear liquid [water without food coloring].  The similarities were in the amount of liquid, the weight, and the viscosity.  The only difference appeared to be in the color.

Pat then took two beakers about 25% filled with yellow liquids [water with food coloring and Karo® Syrup, respectively].  This time the colors and volumes were the same, but the density and viscosity were different.

Pat then asked us to compared the red beaker containing red liquid with a red ball.  The only evident similarity was in the color, whereas the states [liquid versus solid] were different, there were different volumes, and the liquid would not bounce off the table.  

Pat then asked us to compare two red balls. The color, size, and state were the same, but the balls did not bounce in exactly the same way.

Pat then asked us to compare a red ball with a steel ball.  They were both balls of about the same size, but with different masses, densities, colors, and bouncabilities.

We then compared a large cube with a small one.  Finally, Pat held up a roll of tape, and asked us to list its physical properties:  hollow, strong, wide, sticky, black, moveable, cylindrical, etc.

Pat also distributed a handout sheet containing the following questions:

  1. Study the contents of two beakers.  How are they similar?  Different?  List the similarities and differences.

  2. Same questions, with different beakers

  3. Same questions, with different objects.

  4. Same questions, with different objects.

  5. Same questions, with different objects.

  6. What did you use to tell whether the objects were similar or different?  Did these properties change as you made your observations?

  7. To test your knowledge, list 5 physical properties for the object being displayed.

Good exercises in observation!  Thanks, Pat!

23 March 2004: Ben Stark  [IIT Biology]         The Can Crusher
Ben
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!

12 October 2004: Ron Tuinstra [Illiana Christian HS, Chemistry]                   Density and Significant Figures (Handout)
Ron handed out a sheet with the following exercises (we did the first two in today's class):

  1. Find the density of one of the density cubes using a ruler (always metric) and the electronic balance. Remember to measure correctly and use correct significant figures. Compare your answer to the correct answer and find the error.
  2. Determine the thickness of aluminum foil by finding the mass, density of aluminum (from chart), length, and width. Again, use significant figures properly.
  3. Find the density of an unknown irregular solid using a graduated cylinder and electronic balance. Be sure to measure correctly and use correct significant figures. Identify the solid by comparing the density to the chart given. Calculate the percentage of error.
Ron had ten cubes of identical or nearly identical size, made of various materials, and these served as the "experimental materials" for the first exercise. Our density measurements for materials were off (compared to known values for each material) usually by 5-10 %. We checked our balance with standard weights, and the balance was fine. We guessed that probably our dimension measurements may have been the source of the error.

For the second exercise, we use the equations for density D in terms of mass M and volume V of a material  D = M / V. In addition, we used the formula for the volume V of a rectangular sheet in terms of its length L, width W, and thickness T; namely  V = L ´ W ´ T. Once we measure the width W and length L  of a rectangular piece of aluminum foil, we have all the information  needed to calculate its thickness:

T=M / [L ´ W ´ D]
Matt Collier, Chris Etapa, and Ken Schug all calculated the thickness of aluminum foil at T = 0.16 mm = 0.006 inches, which seems quite reasonable (we do not have an independent value for this thickness).  Good stuff, Ron!

12 October 2004: Ken Schug  brought a sealed silvery glass vial into which we could not see. Ron rocked it gently and it seemed to have a solid in it, but when the vial was warmed in Ron's hand for a minute or two, we could see that there was a liquid inside. It was Cesium metal inside, which has a melting point just above room temperature.  Caution:  Cesium metal is highly corrosive -- do not come into contact with this substance!


Ken had a stoppered Erlenmeyer flask almost filled with a blue liquid with a pipette vertically held in the stopper with one end submerged in the flask and some of the blue liquid in the pipette. He put the flask on ice to cool. The column of the blue liquid in the pipette slowly fell as the temperature of the liquid decreased, because of a decrease in the volume of the fluid.  It worked as a thermometer! Ken then pulled out a very long thermometer, which we presumed to be useful over a large range of temperatures. But it had a very large mercury bulb compared to its size, which allowed this huge thermometer to range only over 13 Celsius  degrees, and thus be very precise.

23 November 2004: Walter Kondratko [Steinmetz HS]             Melting Points
A handout contained the following information:

Walter brought 6-8 sets of apparatus that let us measure the melting points of chemicals accurately and easily. The instruments have a port into which a thin capillary tube containing an unknown (solid) chemical is placed, and a microscope which looks in on a hole in the port so that we can see whether the material in the tube is solid or liquid. A thermometer simultaneously records the temperature in the port, so that the melting temperature can be determined.  The experiment was a great success with measured melting points generally within about  ± 4 °C of the accepted/standard values.

This was an excellent hands-on lesson!  Thanks, Walter. 

08 February 2005: Terri Donatello [ST Edwards School, science]       Heat Transfer and Density

Welcome back, Terri!
Conduction, radiation, convection are three ways by which heat is transferred, and Terri showed us about them. Terri had made colored ice cubes (food coloring in tap water) and each group placed one in a beaker of room temperature tap water. Then each group took the temperature (with thermometers provided) at the surface of the water in the beaker and at the bottom of the beaker. The temp near the top (actually near the cube) dropped slowly from 22o C to 19 o C, but the temp at the bottom dropped steadily during the same period from 21 o C to 14 o. The water cooled near the cube was denser than the warmer water at the surface and thus sank to the bottom from around the cube, cooling the bottom. In fact, we could see a stream of colored water coming down from the cube, so that a “convection current” was clearly evident.

Next Terri had us repeat the experiment with salt water, which we made by dissolving salt in tap water. The ice cube was tap water, as above. In this case, the water near the cube (at the top) cooled much faster than the water at the bottom, the opposite of our first result. In this case the salt water, being denser than the tap water, impaired the ability of the cold (tap) water from the melting cube to fall to the bottom of the beaker, as the salt water in the beaker and this water from the cube were now about the same density as each other.

Then Terri demonstrated heat by conduction, when heat is transferred by a warmer object touching a cooler object. Here there were two thermos-like cups, one of which was filled with room temperature tap water and the other with hot water. A U-shaped metal bar was then placed with one end in the cold water and the other in the hot water.  We watched the thermometers as heat was conducted through the bar, raising the temperature of the cold water by conduction, and lowering the temperature of the hot water. 

Finally we felt radiant heat by holding our hands near the hotplate that we had used to heat the water.

Terrific, Terri!

29 March 2005: Terri Donatello [ST Edwards, science]                  Physical Properties
Terri followed up on her last miniteach, specifically in her set-up with hot and room temp water (in insulated containers) connected by a metal bar. Actually, from a microscopic statistical viewpoint, heat flows in both directions (from room temp to hot as well as the expected hot to room temp), but the flow from hot to room temp is much greater than the reverse so that the net flow is from hot to room temp. Cool stuff, Terri.