Vanishing clues
Objective: To make what we’ve written on a paper disappear
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Laboratory materials
Cotton swabs
Beakers
White paper
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Reagents
Betadine
Vitamin C (effervescent tablet)
Water
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Questions
What is absorbed when rewriting the message?
Which chemical reaction is taking place?
Procedure
- Saturate the cotton swab with the iodine solution and write a message on a blank sheet of paper.
- Dissolve some vitamin C tablets in water.
- Deep the other clean cotton swab in the vitamin C solution and rewrite the previous message. Observe what happens.
Theoretical explanation
When the iodine from Betadine® touches the paper, a dark-colored complex is formed that contrasts with the white color of the sheet. In the second step, vitamin C (ascorbic acid) acts as a reducing agent and donates electrons to the iodine, thereby reducing it. This results in the destruction of the complex formed by the iodine with the cellulose of the paper, and that’s why the color disappears. The reaction is as follows:
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