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DEMONSTRATION in Indicators. Last updated October 17, 2016.

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Summary

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

Grade Level

High, middle, or elementary school

Objectives

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

Time

Teacher Preparation: 5 minutes
Lesson: 10 minutes

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                                                                            

Safety

  • 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.

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.

Instructions

  1. Use a small paint brush rite a message using the universal indicator 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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