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Another Secret Message (2 Favorites)

DEMONSTRATION in Acid Base Reactions, Indicators. Last updated April 26, 2019.


In this demonstration, students will observe a hidden message while understanding simple acid/base chemistry and indicators.

Grade Level

High, middle, or elementary school

AP Chemistry Curriculum Framework

This demonstration supports the following learning objectives:

  • Big Idea 3: Changes in matter involve the rearrangement and/or reorganization of atoms and/or the transfer of electrons.
    • 3.10 The student is able to evaluate the classification of a process as a physical change, chemical change, or ambiguous change based on both macroscopic observations and the distinction between rearrangement of covalent interactions and non-covalent interactions.
  • Big Idea 5: The laws of thermodynamics describe the essential role of energy and explain and predict the direction of changes in matter.
    • 5.16 The student can use Le Chatelier’s principle to make qualitative predictions for systems in which coupled reactions that share a common intermediate drive formation of a product.
  • Big Idea 6: Any bond or intermolecular attraction that can be formed can be broken. These two processes are in a dynamic competition, sensitive to initial conditions and external perturbations.
    • 6.3 The student can connect kinetics to equilibrium by using reasoning about equilibrium, such as Le Chatelier’s principle, to infer the relative rates of the forward and reverse reactions.
    • 6.8 The student is able to use Le Chatelier’s principle to predict the direction of the shift resulting from various possible stresses on a system at chemical equilibrium.

NGSS Alignment

This demonstration will help prepare your students to meet the performance expectations in the following standards:

  • HS-PS1-6. Refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium.
  • Science and Engineering Practices: Refine a solution to a complex real-world problem, based on scientific knowledge, student-generated sources of evidence, prioritized criteria, and trade off considerations.
  • Crosscutting Concepts:
    • Stability and Change: Much of science deals with constructing explanations of how things change and how they remain stable.


By the end of this demonstration, students should be able to

  • Understand that a chemical change is taking place.
  • Recognize that an indicator causes the color change.
  • Realize that an acid base reaction is taking place.

Chemistry Topics

This demonstration supports students’ understanding of
  • Indicators
  • Acid/base reaction
  • Neutralization


Teacher Preparation: 5 minutes

Lesson: 10 minutes


    Demo anothersecretmessage materials
  • Roll of paper towels
  • Phenolphthalein Indicator solution
  • Cleaning supply with ammonia in a spray bottle
  • Vinegar in a spray bottle
  • Small art-type paint brush


  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
  • Students should wash their hands thoroughly before leaving the lab.

Demo anothersecretmessage teachernotes1

Teacher Notes

  • Phenolphthalein Indicator solution is often used as an indicator in acid/base titrations.
  • Phenolphthalein is a weak acid with the formula C20H14O4. It is often written as “H-In”. In an acidic environment it is colorless. In a basic environment it will donate a proton (H+1) and the resulting anion (In-1) is pink.
  • This demonstration is often used to welcome students and parents to your classroom at the beginning of the school year. It can also be used to introduce the concept of indicators and acid-base titrations.


  1. Use a small paint brush write a message using the phenolphthalein solution on a paper towel.
  2. Allow the paper towel to dry completely.
  3. Hang paper towel on the front of your desk or lab table.
  4. Spray the paper with the ammonia cleaning solution to unveil what you’ve written.
  5. Spray the paper with vinegar to make the message change colors.
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