Universal Indicator Rainbow Trout

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In this activity, learners cut out a fish and then "paint" it using universal indicator and acids and bases. The initial coat of indicator changes the color of the paper (it will turn a salmon color if the paper is acidic, and green if it is considered acid-free). From there, adding acids (such as lemon juice) and bases (such as laundry detergent) will further change the color. Universal indicator responds to a wide range of acids and bases, so other home chemicals (shampoo, vinegar, etc.) could be tried to create different colors. For older learners, a paper pattern other than a "rainbow trout" (such as a rainforest bird or other colorful animal) can be used.

Quick Guide

Preparation Time:
5 to 10 minutes

Learning Time:
10 to 30 minutes

Estimated Materials Cost:
$1 - $5 per student

Age Range:
Ages 4 - 14

Resource Type:

English, Spanish

Materials List (per student)

  • Universal indicator solution (available from chemical supply houses)
  • Lemon juice
  • Liquid laundry detergent
  • Index card or piece of acid-free cardstock with nonshiny finish
  • Rainbow trout (or other animal) pattern
  • Masking tape
  • Paintbrush
  • Cotton swabs
  • Water
  • 3 small plastic cups
  • Paper towels
  • Pencil, pen
  • Scissors
  • Teaspoon


  • Physical Sciences
    • Chemistry
      • Acids and Bases
      • Solutions

Informal Categories

  • Animals
  • Arts and Crafts


To use this activity, learners need to:

  • see
  • see color
  • touch

Learning styles supported:

  • Links STEM to other topics of interest such as arts and humanities
  • Involves hands-on or lab activities


Access Rights:

  • Free access