Acids & Bases: Cabbage Juice pH Indicator

Acids and bases are found in a variety of everyday items, including food and drink, medicine, and cleaning products.  In this lab, we will learn about what makes an acid or base “strong,” and use the juice from red cabbage to test the pH of common household liquids and perform neutralization experiments.

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Student Version
Student Advanced Version

Teacher Version

Recommended Prerequisites:
  • The advanced lab addresses the concept of a logarithmic scale, and does some basic calculations.  Probably appropriate for late-middle school or high school students.
Key Concepts:
  • The pH of a solution is determined by the concentration of specific ions.
  • Ions are negatively or positively charged atoms. If a solution contains extra hydrogen ions (H+), it is acidic. If a solution contains extra hydroxyl ions (OH), the solution is basic, or alkaline.
  • Strong acids have a high percentage of their atoms found as ions (ie unbound), whereas weak acids have only a low percentage of ions in solution.
  • The pH scale ranges from 0 to 14 in water. The closer to 0, the stronger the acid, whereas the closer to 14, the stronger the base. A pH of 7 is neutral, or neither basic nor acidic.
  • When an acid and a base are mixed, the hydrogen ions from the acid bind the hydroxyl ions of the base, forming water. This is referred to as neutralization of the acid and base.
  • Colored & silver paper clips
  • Pre-cut cabbage
  • Blender
  • Strainer
  • Large container
  • Measuring spoons
  • 7+ clear plastic cups (depends on how many things you’re testing)
  • Lemon juice
  • Baking soda
  • Shampoo (preferably clear)
  • Glass cleaner (with ammonia)
  • Milk of Magnesia
  • Warhead Sour Spray or sour candy, such as Sour Patch Kids
  • Other options include: vinegar (pH 2-3), apple juice (pH 4)
  • Eye droppers
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