High School Biology-Chemistry SMILE Meeting
14 December 2004
Notes Prepared by Porter Johnson

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!!

Ron Tuinstra [Illiana Christian HS, chemistry]               Human response times
Ron brought this back from a National Association of Biology Teachers convention. It is fast, fun, and yields quantitative data. The detailed protocol is in the handout. Briefly, a vertical meter stick is dropped by one member of a two person team through a space between the other (catcher) person's thumb and index finger.  The "catcher" grabs the stick by closing his/her thumb and index finger on it.  The distance the stick falls between the start signal and the catching can then be easily measured by subtracting the "starting position (which we set at 10 cm, i.e., the initial thumb and index finger position was always put 10 cm from the bottom end of the stick) from the position on the stick at which the grab stopped the stick. We tried visual, auditory, and tactile signals to alert the catcher of the simultaneous release of the stick. Note that the data are collected as distance along the meter stick (i.e., the distance the meter stick falls from the initial signal until the stick is grabbed), which we use as a measure of time. The standard formula obtained from Newton's Laws of motion allows a conversion from distance to response time.

We predicted before we did the experiment that the response time would be fastest for the visual start signal and slowest for the tactile start signal (with the auditory signal intermediate). This is based on our idea that receipt of the signal should be fastest for light, next fastest for sound, and slowest for transmission along the nerves in the arm from the hand to the brain (for tactile). For all subjects all response times were in the 140 - 300 msec range, but with different averages for males and females. Here are the data:

SexNumberVisual  Auditory Tactile 
Female2 210 msec   200 msec  235 msec
Male4215 msec   305 msec    186 msec
Although our sample size was small, we did find Male /Female differences and the surprise was that the tactile signal was the fastest for males in our sample. Here are the average results for Ron's class of teenagers:
SexVisual  Auditory Tactile 
Boys   184 msec   230 msec  216 msec
Girls  192 msec   235 msec    205 msec

Within experimental error there seemed to be no M/F differences, but visual response was faster for the younger subjects than for us older folks! Ron said that in his experience for his students, usually V is fastest, then T, then A.

Ron said that student age and sex would be appropriate parameters for examining average response times. Ed Scanlon suggested left hand versus right hand (or really strong versus weak hand) as another interesting parameter to test.

And Ron, thanks, too, for another great miniteach!

Notes prepared by Benjamin Stark.