Although I respect the right of Espenson to object to my suggestion of a useful teaching aid, I fundamentally disagree with the argument put forward. A good teacher uses a variety of teaching styles and aids to stimulate and educate students, including, if appropriate, “trickery” or showmanship. I have used this demonstration many times with various groups of students over a number of years and it has always produced the desired results, that is, students enjoy this demonstration and—this is the key point—they do remember the take home message that substances are only catalysts if they bring about a reaction without being consumed in the process. Can Espenson guarantee the same about his suggested procedure for carrying out this demonstration? I think not, especially since adding the iodide last still produces, albeit more slowly, the black I2–starch coloration!
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