Iodine Clock Reaction
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Solution A (4L): 4g starch, 1.8g Na2S2O5
Solution B (4L): 2g KIO3, 120ml 1M H2SO4

Pre-mix (boil) starch and add when cool. Completely dissolve each component 
before adding next. 

Demo: add equal amounts (suggest 150ml each) to (400ml) beaker. 
Mix contents of beaker back and forth 3 times then observe. 
Reaction takes about 25 seconds. Decrease time by increasing H2SO4. 

Variations: vary temperature, vary pH, vary concentration