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AUGUST 2010 OUT NOW!
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ASK . . .
DR GRUGNI
DR VIBHA
THE DOCTOR
MISS MICHE
YOUR OPINION COUNTS
TELL US WHAT YOU THINK OF THE TEENAGER
BACK ISSUES
WRITE FOR US
SIMPLE SCIENCE
WHAT YOU’LL NEED
- Iodine
- Liquid starch (such as you would use when washing clothes)
- Vitamin C tablet
- Large glass or clear plastic pitcher
- Large jar or bowl (you need to be able to fit your hand inside)
WHAT YOU DO
- Assemble your audience. Put a few drops of iodine into the pitcher. Add water and stir until the solution turns light yellow.
- Pour the liquid starch into the jar/bowl. Dip one of your hands into it.
- Put your clean hand into the iodine-water solution and stir it around. Nothing happens.
- Now put the hand you dipped into the starch solution in the iodine-water solution and stir it around. The solution will turn dark blue. Tell your audience this is chemistry at work.
- Meanwhile, without letting your audience see the vitamin C tablet, pick it up with the hand you placed in the iodine-water solution and hold it in your palm. Put this hand in the dark blue solution and stir. Say that magic is more fun than chemistry as the tablet dissolves and the solution turns clear. (Don't forget to wash your hands after this trick)
WHAT HAPPENED?
This trick works due to the chemical reaction between the starch and iodine and then the starch-iodine solution and Vitamin C. The iodine which turns the water yellow is an indicator for starch. When starch is present the iodine solution will change into a deep blue colour. This is because starch contains a molecule called amylase that is shaped like a coil. The iodine gets between the coils. This makes the solution blue because the starch-iodine solution absorbs all wavelengths of light except blue. When you add the Vitamin C tablet it makes the iodine change into iodide and the solution becomes clear.
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