Lemon juice and iodine invisible inks

Message written with lemon juice appears when paper is treated with iodine solution.

Scientific name: Vitamin C prevents complex formation between iodine and starch.

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Safety

Wear eye protection goggles.

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

(C6H10O5)n + I2 → I2*(C6H10O5)n

I2 + I- → I3-

C6H8O6 + I3- + H2O → C6H6O6 + 3I- + 2H+

Step-by-step instruction

  1. Take a paint brush and write a message with lemon juice.
  2. Prepare iodine solution in a petri dish. Pour a few milliliters of iodine tincture in a petri dish and dissolve it in water.
  3. Put the paper in the petri dish or coat it with iodine solution using a paint brush.
  4. The text will stay white while the rest of paper will turn blue.

Scientific background

In this experiment lemon juice developed by iodine solution is used to prepare invisible inks. When paper with written message is treated with iodine solution the starch contained in paper reacts with iodine to form a colored complex:

(C6H10O5)n + I2 → I2*(C6H10O5)n

The paper turns blue but the message still stays white. Lemon juice contains vitamin C which prevents the reaction between starch and iodine:

I2 + I- → I3-

C6H8O6 + I3- + H2O → C6H6O6 + 3I- + 2H+

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Published on 23 March 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst