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

NaCl          KCl            CuCl2         SrCl2           Unknown Chloride
She added some methanol to each, and with the shades down and lights off, Pat lighted each dish. As the methanol burned, it heated up a bit of the salt in each dish, resulting in a different colored flame for each; The display was beautiful! The color of each is characteristic of the cation (metal ion), the only element differing among the dishes (because all are chloride salts). The heat excited electrons of each cation; the return of the electrons to their ground states was of characteristic quantum, and thus color. The chloride electrons relax with a quantum that is an energy and wavelength that is not in the visible range.

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/

The plan is to investigate various colors of food coloring, to see whether any contain multiple components with different colors. We put about 1/2 ml of each color into a ceramic dish with little wells, from which we were able to make "spots" using inexpensive plastic "bulb" type droppers. [Ken Schug said that toothpicks dipped into each color are a great way to produce "tight" spots.]  We laid out a piece of special chromatographic paper, and put pencil marks on it for four types of food coloring [see picture]. Then we put the paper into a beaker containing 0.5 cm of water, being careful to keep the paper from touching the sides of the beaker to reduce "smiling" of the lines, and making sure that only the bottom of the paper, but not the spots themselves, was submerged.
We made the following determinations about the various food colorings:
 Yellow  Predominantly yellow, with a little orange mixed in
  Green A mixture of yellow and blue, as expected
   Blue Blue with a little (unexpected) pink
   Red Predominantly red, with a little pink
It also appears from the values of Rf, which is defined as the distance from the spot to the center of the color track divided by the distance traveled by water on the chromatogram, that the "blue" in blue and green food coloring and the "yellow" in yellow and green food coloring are probably the same dyes. In other words, the food coloring factory probably uses relatively few basic colored compounds in various proportions to produce all the colors.

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:

A: Salt (NaCl); B: Baking Soda; C: Baking Powder; D: Soluble Starch

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.

We presented the findings in the following data sheet:

  Solids Color Texture Reaction with
Liquid I
Reaction with
Liquid II
Reaction with
Liquid III

Pure
Substances
A: Salt          
  B Baking
Soda
         
  C Baking
Powder
         
  D: Starch          

2 Substance
  Mixtures
1          
  2          
  3          

3 Substance
  Mixtures
4          
  5          

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.
Here is a summary of material properties:

Data and Observations

Substance Did it Melt? Did it dissolve
in water?
Did the solution
conduct electricity?
Classification
KCl No Yes Yes Ionic
Aspirin Yes Partially No Molecular
Fructose Yes Yes No Molecular
Paraffin Yes No No Molecular
Epsom salt No Yes Yes Ionic
Table sugar Yes Yes No Molecular
Table salt No Yes Yes Ionic

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:

HCl + NaOH ® NaCl + H2O.
We counted out 10 drops of "unknown" HCl (hydrochloric acid) into a "well" in the Chemplate™ , added one drop of phenolphthalein "indicator" (this compound is pink in basic solution and colorless in acid.) We then added the NaOH (sodium hydroxide) solution while stirring until the solution turned (and stayed) pink. The concentration (conc) of the acid could then be calculated from the following relationship:
# drops of base / # drops of acid = conc of acid / conc of base
Pushpa, assisted by others, then tried the "egg in a bottle" demonstration of air pressure and was eventually successful in getting a shelled, hard-boiled egg to enter a juice bottle with an opening smaller than the egg without pushing it. They dropped a burning piece of paper into the jar and placed the egg gently in the opening. At first nothing happened, then we saw the egg slowly slide into the jar untouched by human hands! We were not as successful at removing the egg (by blowing into the inverted bottle) and decided that the demonstration would work better with a larger container. [The burning paper heats the air in the bottle, so when the egg blocks the entrance and the air cools, the pressure decreases and becomes less than the atmospheric pressure outside the jar, which pushes the egg into the jar.]  Good stuff, Pushpa!

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 torchLarry 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:

Good, clean, interesting chemistry.  Thanks, Estellvenia!

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:

Good, clean, interesting chemistry.  Thanks, Estellvenia!

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:

Pen Color   Color Streaks Seen
Orange orange (only)
Tan pink, red, brown
Black dark blue, pink, red, green
Thanks for the ideas, Bill!

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.
We tested several alkali metals (K: potassium, Li: lithium, and Na: sodium), as well as Ca: calcium, Cu: copper, and Sr: strontium. We used our "standards" to determine unknowns from their colors.

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.

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!