Here's a fun activity that serves as a High Yield activity that can be used for Project Learn, STEM, and to meet a badge requirement for Junior Girl Scout Detective Badge and the vintage Brownie Girl Scout Try It Science Wonders.
Target Area: Science Lab, Art Studio, or Cafeteria
Objective: Members learn how chemistry is used practically in real life.
Target Age Group: Tweens Age 10-12 years
Time to Complete: one 45 minute rotation
Materials Needed: lemon juice (other safe liquids are optional), paper, heat source (iron or light bulb) and paint brushes or cotton swabs
Instructions:
Ask members how they would pass secret messages if they were spies. After giving them time to share their answers, tell them some stories of spies how used secret ink to pass messages.
FOR STAFF/VOLUNTEER USE: Science Daily Article
Using lemon juice, have members write or paint a short, secret message on a piece of paper. After letting each piece of paper dry, members trade papers and use heat to reveal the words. Lightbulbs and irons are sufficient heat sources to reveal the letters. Be careful not to burn the paper when revealing the letters.
Ask the members why they think this happens. Explain that this is possible due to the chemistry involved. In the case of lemon juice, its acidity makes it easily oxidize (combine with oxygen in the air) when heated, which makes the paper turn browner where the lemon juice has been applied.
Encourage members to experiment with other liquids including milk, soda, juices, and other safe liquids. What can be used for secret writing? (Orange juice, vinegar, and apple juice will react similarly.)
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