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Discovery Labs: INVISIBLE INK

OBJECTIVE:

Explore acid-base chemical reactions by creating invisible ink that reveals hidden messages with heat or a chemical reaction.


Can you write a secret message that only appears when the paper is heated or with a special solution? Let’s find out!


WHAT YOU NEED:

For Lemon Juice Ink (Heat-Reveal):

  • Lemon juice (or vinegar)

  • Cotton swab or paintbrush

  • White paper

  • Hair dryer or iron (with adult supervision)


For Baking Soda Ink (Chemical-Reveal):

  • Baking soda

  • Water

  • Cotton swab or paintbrush

  • White paper

  • Grape juice (100% juice, not drink mix)


INSTRUCTIONS:

Lemon Juice Method:

  1. Dip the cotton swab in lemon juice and write a message on white paper.

  2. Let the paper dry completely—your message will become invisible.

  3. Gently heat the paper using a hair dryer or place it under a warm iron (adults only!).

  4. Watch your secret message appear in brown!


Baking Soda Method:

  1. Mix equal parts baking soda and water to create “ink.”

  2. Use a cotton swab to write a message on white paper.

  3. Let it dry.

  4. To reveal the message, paint over it with grape juice.

  5. Your message will appear in a different color due to a pH reaction!


OBSERVATION:

Watch how heat or a chemical reaction causes a previously invisible message to appear. Note the color changes and how long it takes for each method to reveal the writing.


EXPLANATION: Why Does the Ink Appear?

Lemon juice is an organic compound that weakens paper fibers. When heated, it oxidizes faster than the rest of the paper, turning brown and revealing the writing.


Baking soda is a base. Grape juice contains pigments that change color in response to pH levels. When the acidic juice meets the basic baking soda residue, a visible chemical reaction occurs.


CONCLUSION:

This experiment combines chemistry with creativity. It demonstrates acid-base reactions, oxidation, and pH indicators in a hands-on, memorable way. Plus—it’s like becoming a spy!


EXTENSION:

  • Try other household acids and bases to write or reveal messages (e.g., milk, cola, soap solution).

  • Research how pH indicators work and explore natural ones like red cabbage juice.

  • Turn this into a spy-themed activity: write and decode secret messages as a group!




 
 
 

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est. 2023
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