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Can a Cabbage Distinguish an Acid from a Base? (0 Favorites)

LAB in Observations, Acid Base Reactions, Indicators, Chemical Properties. Last updated June 28, 2018.


Summary

In this lab, students will first determine what colors the cabbage indicator turns in acidic, neutral, and basic solutions. This lab provides outreach to elementary level students to get them excited about and interested in chemistry because high school chemistry students prepare and execute the activity. The high school students prepare the cabbage juice indicator, standard test solutions, and household materials that they analyze with the elementary school students.

Grade Level

Elementary, middle, or high school

Objectives

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

  • Use cabbage indicator to detect acid, neutral, or base properties of a solution.
  • Understand the acid base pH scale.

Chemistry Topics

This lesson supports students’ understanding of

  • Acids and bases
  • pH
  • Indicators

Time

Teacher Preparation: 60 minutes

Lesson: 45 to 60 minutes

Materials

  • Cabbage indicator
  • Dropper bottles
  • Solutions with known acid, neutral, or base properties
  • Household items
  • Crayons or colored pencils

Safety

Always wear safety goggles when working with chemicals.

Teacher Notes

My district wants to encourage and support STEM education. We have found through survey and observation that students have been lacking engagement in science activities as a result of increased pressure in mathematics and ELA. We also have found that of subjects taught by elementary teachers, science is usually the one with which they are least comfortable. The younger students were excited to interact with the high school students. This also provided a unique leadership opportunity for our high school students as they discussed acids and bases with students during this activity.

For the Student

Lesson

Background

Chemistry students have prepared cabbage juice and have set up workstations in the classroom for you to explore acids and bases. You will use your observations to classify some common household items as acids, neutral substances, or bases.

Red cabbage contains a pigment molecule known as an anthocyanin. This same pigment gives many other items in nature a bright red color. Apples, plums, poppies, grapes, cornflowers, and red maple leaves in the fall all contain anthocyanins. The color you see is dependent upon the pH, or relative acidity, of the chemical’s surroundings.

When the pH for a substance is 7, it is neutral. If the pH is lower, it is acidic. If it is higher, it is basic. The further the pH is from 7, the more acidic or basic the substance. The human stomach is typically a pH 1–2 because hydrochloric acid is produced by cells in the lining. Acid is important in stomachs because it helps break down food.

Safety

When working with chemicals, it is necessary to work carefully and to wear an apron and goggles.

Procedure

You will test solutions that are known by the chemistry student to be acidic, neutral, or basic. You will use this information to determine the color you expect at various values along the pH scale. Once you’ve established the pH key, you will test household substances to determine if they are acidic, neutral, or basic.

Have crayons or colored pencils handy to color in the rounded-cornered rectangles in each row of the table under the color heading. The chemistry students will help you with this part. You will use pipets and either test plates or small test tubes to mix cabbage juice with each of the substances that you are testing.

Known solutions

Substance pH Color

Now test some household substances to identify them as acidic, neutral, or basic.

Substance Color Acid, Neutral, or Base pH estimate

Analysis

  1. What did you learn from this experiment?
  2. Did anything surprise you?
  3. From this experience, how can you identify an acid from a base?
  4. What is your favorite area of science to learn about?