High School SMILE Meeting 1999-00 -- 05-06 Academic Years Chemical Analysis

28 March 2000: Ben Butler (L Ward School)
showed us "C-Spectra." (handouts) He set up a discharge tube apparatus on the table, and plugged a hydrogen discharge tube into it. The tube has hydrogen in it, and a high voltage is applied to electrodes at its ends, which produces excited (high energy) hydrogen atoms, resulting in the emission of light. But the light was not white light which has a continuous spectrum of color. The hydrogen atoms emitted light of only certain colors, and we could see the separate colors by viewing the light through a holographic diffraction grating (C-Spectra) film. We saw colored spectral lines of red, blue and violet from the hydrogen. When Ben replaced the hydrogen tube with one containing mercury atoms, we saw spectral lines of yellow, orange and violet. A tube containing water molecules produced the same spectral colored lines as hydrogen (surprise?!), and a tube with argon showed us red, orange, blue and violet lines. The handouts gave some explanation and descriptions of spectra obtained from various elements (gases) within the tubes.

Ben showed us an absorption spectrum next. He shined white light through a solution in a transparent container, and we viewed the light coming through with our C-Spectra holographic diffraction gratings. Sure enough! When the white light was spread into a continuous rainbow spectrum, dark bands appeared in place of the colors that would normally be there in the spectrum. Those particular colors were being absorbed by the solution, and could not get through to be observed by us. Very nice, Ben! Thanks!

05 September 2000: Pat Riley (Lincoln Park HS)
got us actively involved in chemistry: Acid, Base or Neutral? In teams of two we tested six solutions contained in microtip plastic droppers with bromothymol blue indicator using a clear plastic, 24 well plate. (handout) We had to figure out which solutions were acidic, basic or neutral. And infer relative strengths. Neat! Thanks for sharpening our chemistry, Pat!

24 October 2000: Pat Riley (Lincoln Park HS) did the Flame Test. Each of five porcelain evaporation dishes (about 50 ml  Pyrex™  beakers may be used instead) contained an aqueous solution of one of these salts

Pat then passed out goggles which diffracted white light. With the goggles on we looked at white light and saw a complete and continuous rainbow of color. Then Pat turned on a red neon light. With goggles on the red light gave us a line spectrum, with only certain colors of the rainbow visible (red, green, yellow, purple) as colored lines, and darkness between the lines. The lines have colors (wavelengths) characteristic of electron energy changes in the neon ions and the quanta emitted corresponding to those changes.

This was repeated with argon light which looked lavender without goggles. With goggles there were blue lines and a few others, ie, a different line spectrum from neon.

This was an absolutely outstanding mini-teach!  See also the SMILE presentation by Theresa Fichera [Frazier School] ch9105.html.

07 November 2000: Pam Moy (Morgan Park HS)
showed us a jar containing a green fluid. It was an extract made by soaking spinach leaves in ethyl alcohol for a week (one day was sufficient to leach out the color). She gave each group of two of us an 8 oz styrofoam cup into which the dark green spinach extract was poured to a depth of about one inch. A strip of coffee filter was placed with bottom end submerged in the extract, and the top end taped to side of the cup. Then we went on to the next presentation, and after about an hour and ten minutes we came back to this experiment and observed the strips. There was a dark green band of color at the bottom, then a light green band followed by a yellow band. The process we had performed is called "chromatography," and the strips with the colored bands are called chromatograms. The differently colored bands come from different chemical pigments in the spinach (chlorophylls, etc), which diffuse at different rates through the wet paper strip.

An inexpensive but most informative experiment, and a great introduction to many topics: chromatography; plant chemistry; diffusion rates of different molecules; color differences associated with different molecules...and probably others. For additional ideas see the website http://www.chemguide.co.uk/analysis/chromatography/paper.html. Thanks, Pam!

23 October 2001: Lee Slick (Morgan Park HS)
Lee came dressed as a wizard! He poured a clear liquid from one flask into another containing clear liquid --- the result was a pink liquid!  Then, he poured the pink liquid into a third flask containing a clear liquid--the result was a clear liquid.  Lee had been demonstrating pH Indicators.  He did not address the question of the difference between a witch and a warlock, however.  For a discussion of that topic, see http://www.absolute-fantasy-art.com/witches-warlocks.html and http://hometown.aol.com/divadelaluna/.

19 March 2002: Pushpa Bahl (Collins HS) -- Handout: Paper Chromatography of Food Coloring
Pushpa explained that paper chromatography is used to separate individual substances in a mixture.

"Chromatography is a process which separates the substances in a mixture. The relative sizes of molecules or the charges on ions influence the rates of separation. Gas chromatography separates mixtures of gases and volatile liquids, using metal columns which are thin and very long. Column chromatography uses a liquid medium to separate complex substances such as vitamins, proteins, hormones and DNA. Gel electrophoresis is a form of chromatography used to separate fragments of DNA by their size and electrical charge. Paper or chalk chromatography is used to separate the components of dyes, inks, food coloring and other mixtures by their molecular size and their solubility in polar solvents-- such as water and alcohol."
Source Lawrence Livermore National Laboratory Science & Technology Education Program:  http://education.llnl.gov/

This was a terrific PA, Pushpa!! It was lots of fun, very easy and safe, and showed lots of real science. Ken continued with a discussion of how the migration rate of a spot depends upon its relativity affinity for the paper and water (its "partition coefficient"), and how you can do the same type of experiment by rubbing M&Ms and Skittles on the paper as sources of pigments.

For additional details see the websites http://www.rpi.edu/dept/chem-eng/Biotech-Environ/CHROMO/chromintro.html and http://www.kids.union.edu/fsnChromatography.htm.

11 December 2001: 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!

03 December 2002: Pushpa Bahl [Collins HS]      TITRATION 
Pushpa provided several handouts of background information and directions for a hands-on exercise we would be doing later. She announced that there was a "scientific mistake" on the directions sheet and offered a $2 reward (which she showed us) to the first person to discover it. After several false alarms the oldest person in the room noticed that the word "millimeters" had been used where "milliliters" was intended and claimed the prize. Pushpa described a "drop counting" method for doing titration, which is safer and less expensive (though less precise) than using burettes. She then said we would be doing an acid-base, neutralization reaction (Acid + Base ® Salt + Water), specifically:

10 February 2004: Larry Alofs  [Kenwood HS, Physics]         Flame Tests!
A visitor from the Math-Physics SMILE class, Larry showed that flame tests provide a means of identification of materials.  He had a supply of small "nasal spray" bottles that contained solutions of various ions and salts, as well as a portable torch.  Larry lit  the torch, and then he sprayed a tiny cloud of one of the solutions directly into the flame.  We could easily see the  flame change to a color that was distinctive of the alkali / alkaline metal (lithium, sodium, potassium, calcium, etc) in the solution, which lasted for a few seconds before disappearing.  Sodium, for example, produces a yellow-orange flame color;  potassium produces red.  Every minute or so he sprayed a different chemical into the flame, producing a new color.  The  effect was especially dramatic when we turned out the lights in the room.  These spray bottles produce a fine mist of the solution, which works very well for doing flame tests. 

You really set things on fire! Thanks for popping in and showing us how to do this, Larry.

24 February 2004: Jane Shields  [Calumet Career Academy]         Tie Dye Chromatography
Jane showed some neat stuff that she had learned to do at a workshop held last summer at Navy Pier, which focused upon chromatography, as well as related ideas in adhesion, cohesion, and capillary action.

First Jane gave us "baby food" jars  that contained  a 50 - 50 mixture of isopropyl alcohol and water.  We cut pieces of cloth from an ordinary blank T-shirt --- each piece was roughly square, about 12 cm [5 inches] on each side.  We drew pictures on the cloth, using water-soluble markers.  We then drew a little of the mixture from the jars up into soda straws, using  capillary action.  We dabbed the straw at our drawings and  let out a little of the mixture on top of the images on the cloth.  The fabric acted as the stationary phase, and the alcohol-water mixture as the mobile phase to separate each part of marker image into its constituent colors.   We obtained a sort of "abbreviated spectrum" of colors from the original drawing lines.  Each marker color is a (proprietary, patented, registered, secret) mix of dyes. Even two markers of the same color may be produced from different dyes, since they are made by different manufacturers, and thus give different chromatograms.  Some makers seem to use only a single constituent color, whereas others used mixtures of dyes of different colors.

We now have really "mellow" images,  and have gotten "into" chemistry.  Thanks for showing us how to do this, Jane!

09 March 2004: Jane Shields  [Calumet Career Academy]         Tie Dye Chromatography, continued
Jane followed up her lesson on chromatography by passing out procedures for separating lipstick, as well as water-soluble markers,  into component colors.  For additional details on lipstick chromatography see the article Whose Lips were these?  / Forensic Chemistry by Stacey Endebrock, Hillsboro High School R-III, Hillsboro Missouri, on the SuccessLink website:  http://www.successlink.org/gti/gti_lesson.asp?lid=2083.

Thanks for the info, Jane!

23 March 2004: Jane Shields  [Calumet HSl]         Chemical Indicators, Homemade Litmus Paper, Acids & Bases
Jane 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!

20 April 2004: Estellvenia Sanders  [Chicago Vocational HS]         (Chemistry):  Combining Substances
Estellvenia divided the class into two groups, and gave each group a set of 5 empty test tubes.  She had supplies of 4 different liquid detergents, as well as corn starch and baking soda.  A sample of four liquid detergents was poured into each of 4 test tubes by each group --- a different detergent in each of the group's test tubes.  The 4 detergents apparently had different densities.  She asked us in what ways are the different detergents similar?  Do they .merely have different percentages of water?  Are there other differences?

We put baking soda into 2 of the test tubes that contained detergents, and recorded what happened.  When baking soda was added to the green detergent, it turned blue, and a chunk of the baking soda sank to the bottom of the test tube.  In the yellow detergent a chunk of baking soda floated slowly to the bottom; no color change.  We concluded that the blue detergent contained a pH indicator.  The detergents seemed to be of different density, with the yellow one containing less water than the blue one, because of the different sinking rates for the baking soda.  When we added corn starch to each detergent in turn, it stayed as a clump at the top in each case.  Then we added "neutralizer" (an unspecified clear liquid) to each test tube -- the neutralizer stayed as a layer on top of the detergent in the absence of mixing, forming what a molecular biologist would call a step (density) gradient.

This lesson had been developed by one of Estellvenia's students --- the best in the class!  We studied the lesson and made the following comments on it for Estellvenia and her class:

• The viscosity of the detergent, as well as its density, determines the rate at which solids fall through it.
• Probably there is no decomposition here.  We do see some signs of separating and settling, but there do not seem to be any chemical changes.
• This exercise is an excellent discovery lesson.
• Maybe we should do the experiment twice --- once all the way through with each of the 4 detergents
• Perhaps we should be more quantitative, weighing out amounts, measuring the volumes, etc.

20 April 2004: Estellvenia Sanders  [Chicago Vocational HS]         (Chemistry):  Combining Substances
Estellvenia divided the class into two groups, and gave each group a set of 5 empty test tubes.  She had supplies of 4 different liquid detergents, as well as corn starch and baking soda.  A sample of four liquid detergents was poured into each of 4 test tubes by each group --- a different detergent in each of the group's test tubes.  The 4 detergents apparently had different densities.  She asked us in what ways are the different detergents similar?  Do they .merely have different percentages of water?  Are there other differences?

We put baking soda into 2 of the test tubes that contained detergents, and recorded what happened.  When baking soda was added to the green detergent, it turned blue, and a chunk of the baking soda sank to the bottom of the test tube.  In the yellow detergent a chunk of baking soda floated slowly to the bottom; no color change.  We concluded that the blue detergent contained a pH indicator.  The detergents seemed to be of different density, with the yellow one containing less water than the blue one, because of the different sinking rates for the baking soda.  When we added corn starch to each detergent in turn, it stayed as a clump at the top in each case.  Then we added "neutralizer" (an unspecified clear liquid) to each test tube -- the neutralizer stayed as a layer on top of the detergent in the absence of mixing, forming what a molecular biologist would call a step (density) gradient.

This lesson had been developed by one of Estellvenia's students --- the best in the class!  We studied the lesson and made the following comments on it for Estellvenia and her class:

• The viscosity of the detergent, as well as its density, determines the rate at which solids fall through it.
• Probably there is no decomposition here.  We do see some signs of separating and settling, but there do not seem to be any chemical changes.
• This exercise is an excellent discovery lesson.
• Maybe we should do the experiment twice --- once all the way through with each of the 4 detergents
• Perhaps we should be more quantitative, weighing out amounts, measuring the volumes, etc.

14 September 2004: Bill Colson [Morgan Park HS, Mathematics]           Paper Towel Chromatography
Bill also mentioned the film What the bleep do we know about quantum physics, as one example of how the ideas of science are advertised in the "new age". Finally, Bill explained that his sister, who runs a day care center at a nearby college, uses many interactive exercises for little kids, with explanations and instructions appropriate for their age.  As an example, he illustrated Paper Towel Chromatography. He made large dots on paper towels with marker pens of various colors, and then used a pipette to put several drops of rubbing (isopropyl) alcohol onto the dots and towels.  The various dyes in these colors moved at different speeds in the paper, so that the dots separated into several colors after a few minutes.  Here are the observations:

14 December 2004: Walter Kondratko [Steinmetz S, chemistry]                   Identification of metallic ions using the flame test
Walter passed out a handout which was a modification of one he obtained as a participant in the Chemistry Van Project at Chicago State University.

Walter gave us his third mini-teach in as many sessions; he is our iron man this term! The flame test is a way to identify an unknown metallic ion by the color it emits when heated, in this case with a portable blow torch. The flame excites the electrons in the ion, and when they return to the unexcited state, they emit electromagnetic radiation of an energy (and thus wavelength and color) that is characteristic of each species. This permits the identification.

Procedure [Do not attempt unless fully supervised by a trained professional!] :
1. Obtain a Bunsen burner, a set of water soaked wood splints, a set of appropriate compounds, and a beaker of water.
2. Light the burner.
3. Take a wood splint (one end has been soaked in water) and dip the water soaked end into a solid sample. Only a few crystals of the solid are needed on the end of the wet splint.
4. Hold the end of the wood splint containing the crystals into a burner flame and observe the colors. In some cases, the color is best observed just as the splint is placed into the flame. Place the wood splint in your beaker of water to extinguish it. Record the colors in the chart.
5. Using a fresh wood splint each time, repeat the test with the other samples.
6. Obtain an unknown and test it.

Walter, thanks again!!

22 February 2005: Walter Kondratko [Steinmetz HS, Chemistry]           Mystery Solutions  (handout)
This exercise comes via the ChemVan project sponsored by Chicago State University.

Walter came in with a number of small (25 ml) plastic squeeze bottles (most were clear, but some were brown), each containing a liquid. We started by mixing the 8 "knowns" in pair-wise combinations and noting our observations in the Table provided on the handout. We then repeated the experiment with the 8 "unknowns" and tried to infer from the patterns in the results what the unknowns might be (the "unknowns" were also our "knowns" but not labeled except by letters). Results included the following.

• Formation of a precipitate. (Note the color of that precipitate) For example: AgNO₃ (soluble) + HCl ® AgCl (white precipitate) + HNO₃ (soluble))
• Formation of bubbles. For example: Na₂CO₃ + 2 HCl ® H₂CO₃ + 2NaCl (soluble)
  Followed by by the decomposition reaction
  H₂CO₃ ® H₂O + CO₂ (bubbles)
  

29 March 2005: Ken Schug [IIT Chemistry]      Identifying Gases by Color?
Ken showed us two sealed glass tubes that were brown in color; we could tell by careful observation that the glass itself was not brown, but that there was a brown gas inside. As near as we could tell the two tubes were identical. Ken asked what gasses are colored. Some suggestions were bromine (brownish; Marva); and chlorine and iodine (yellow and reddish; Walter). He then asked what we could do experimentally to investigate this phenomenon further. Ken put the base of one tube in hot water (from the coffee pot) and the other in ice. The cooled one got lighter colored at the end immersed in ice, and a bit of liquid began to form; the heated tube got darker.

The explanations of these phenomena are as follows. NO₂ was the gas; it is brown, but does not have a complete set of pairs of valence electrons. As the NO₂ cools down, NO₂ dimers form to complete the pairs of valence electrons, and this is colorless (and it condenses to a liquid). The process is reversed under high temperatures as the NO₂ dimers have more vibrational energy and tend to break apart.

This led to a very interesting discussion of how absolute zero was determined (from extrapolation of volume versus temperature curves of various gasses to what would correspond to zero volume). Colorful Physical Chemistry. Thanks, Ken!