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Chemical vs. Physical Changes Activity for Kids

Secret Message Writer DIY

  • Duration: 15-30 min
  • Difficulty: Easy
  • Cost: $0 to $5

Use a chemical change to create a secret message!

Material List

  • 1Cotton swab
  • 1Box of baking soda
  • 1Cup of water
  • 1Spoon
  • 1Sheet of white paper
  • 1Cup of blackberries


  • 1Mix 2 tablespoons of baking soda into one cup of water.
  • 2Dip one end of a cotton swab into baking soda mixture and tap off any drips.
  • 3Use the wet cotton swab to write a message in the center of the paper.
  • 4Let the paper dry for about 10 minutes (until the writing disappears).
  • 5To reveal the message, carefully rub the blackberry back and forth across paper.

How It Works

After you write on the paper with the baking soda and water mixture, the water evaporates leaving trails of baking soda crystals. The purple pigment from the blackberry reacts with the baking soda crystals, forming a new substance! Since a new substance is formed, this is a chemical change.

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