Project 1 - Invisible Ink Using Lemon Juice

Last updated at May 8, 2026 by

⚠️ Caution — Perform this activity under the supervision of an adult.
  • Objective — Discover a chemical change that "writes" with heat.
  • What to do — Write a message on a piece of paper using lemon juice as ink and let it dry. The message will become invisible.
  • Reveal step — Now use a warm iron over the paper (or hold the paper carefully over a candle flame, taking care that it does not catch fire).
  • Observation — The invisible letters turn dark brown as the paper warms.
  • Reflect — Lemon juice is an acid. When heated, it reacts with the paper (which is mainly carbon-rich) and "browns" before the rest of the paper. Can these changes be reversed?
  • Type of change — The browning is a chemical change (new substances formed in the paper); it cannot be reversed.
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CA Maninder Singh

CA Maninder Singh is a Chartered Accountant with 16+ years of practical experience and 20+ years of teaching experience. At Teachoo, he simplifies Accounts, Tax and GST with step-by-step examples so students can apply concepts confidently in exams and real life.

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