Forwards and Backwards: pH and Indicators

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Visitors prepare six solutions combining vinegar and ammonia that range incrementally from acid (all vinegar) to base (all ammonia). They add an indicator to each solution and compare the resulting colors to those on a pH scale chart. Visitors then use a flask containing water and indicator solution. They add drops of ammonia and vinegar, experimenting with the number of drops it takes to change the color of the water (indicating pH) from acid to base and back again. Visitors learn about pH and the pH scale, and about acid and base solutions. They learn that they can test for pH with an indicator solution. They also learn that some chemical reactions are reversible.

Quick Guide

Preparation Time:
30 to 45 minutes

Learning Time:
Under 5 minutes

Estimated Materials Cost:
$1 - $5 per group of students

Age Range:
Ages 6 - adult

Resource Types:
Activity, Experiment/Lab Activity


Materials List (per group of students)

  • One microplate — six wells across
  • 125-ml flask
  • Household grade ammonia (keep 32 oz on hand)
  • Two 150-ml dropper bottles
  • Vinegar (keep 32 oz on hand)
  • Universal indicator (keep 4 oz on hand)
  • One 30-ml dropper bottle


  • Engineering and Technology
    • Engineering
      • Chemical Engineering
    • Technology
  • Physical Sciences
    • Chemistry
      • Chemical Reactions
      • Acids and Bases
      • Solutions
  • Life Sciences
    • Human Body
  • The Nature of Science
    • Science and Society
  • The Nature of Technology
    • Technology and Society
      • Technology and the Environment


To use this activity, learners need to:

  • see
  • read

Learning styles supported:

  • Involves hands-on or lab activities


Components that are part of this resource:

This resource is part of:

Access Rights:

  • Free access



Funding Source:

  • National Science Foundation