Everyone loves a good mystery. From secret codes to crime scene investigation to scavenger hunts, mystery activities help students improve their reasoning and analytical skills while reinforcing reading, math and science concepts in a fun and engaging way. With this cool chemistry activity, students will explore the oxidation process while revealing a hidden message.


  • Paper
  • Lemon juice
  • Bowl
  • Cotton swab
  • Light bulb


  1. Divide students into groups of two or four (depending on class size), and give each group one sheet of paper, one cotton swab and one bowl of lemon juice.
  2. Have students dip a cotton swab in the lemon juice and write a message on the paper.
  3. Once the juice dries, the message should not be visible on the paper.
  4. To reveal the message, hold the paper near a bare incandescent light bulb. Can you see the message? How do you think it works?

Lesson: The message was revealed to due a process called oxidation. Lemon juice contains carbon compounds, which are colorless at room temperature. The heat from the light bulb breaks down these compounds, releasing the carbon. Once the carbon comes in contact with the air, the acid compounds in the lemon juice will oxidize and turn brown before the paper starts to burn.

This activity was adapted from Summer Sizzlers & Magic Mondays: School-Age Theme Activities.