Did you know that digestion begins in your mouth?  Did you know that iodine turns black when reacted with starch?


  • Make sure you have an adult helping you.
  • DO NOT EAT any of the iodine - it's poisonous!


  • Liquid Iodine (the kind you get at a pharmacy)
  • Two crackers (salt free soda crackers work best)
  • Two plates


  1. With your hands, crumble one of the crackers on the first plate and add a drop or two of iodine - what happens?  (DO NOT EAT the cracker with iodine on it)
  2. Then take the second cracker (not the one with iodine on it) and chew it in your mouth - chew well - really get it nice and mushy.  Here's the gross part... Don't swallow,  spit the chewed up cracker onto the second plate.  Now, put a drop or two of iodine on the chewed up and spit out cracker.  What happens?


  • What color is the iodine before you add it to the crackers?
  • What color is the iodine after you add it to the whole cracker?
  • What color is the iodine after you add it to the chewed up/spit out cracker?
  • Can you use iodine to find more starch in your kitchen?  (hint - try cornstarch, potatoes, etc...)

What's Happening?!?

An enzyme in your spit starts digestion right away by converting the big starch molecules in your mouth to small little sugar molecules!  Sugar doesn't turn black when added to iodine (try it!) so, there's no reaction!  Gross, huh?