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.
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:
|Female||2||210 msec||200 msec||235 msec|
|Male||4||215 msec||305 msec||186 msec|
|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.