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Cabbage Chemistry

Difficulty
Time Required Very Short (≤ 1 day)
Prerequisites none
Material Availability Readily available
Cost Very Low (under $20)
Safety Requires adult supervision—some household solutions can be poisonous when mixed together or swallowed.

Abstract

This experiment is for all the kids out there who love boiled cabbage! You say you do not like cabbage? Well maybe you will like this amazing color-changing liquid you can make with cabbage. Which solutions around your house can make the cabbage juice change color? Find out while you learn about acids and bases and how to test for them.

Objective

Make your own pH indicator and use it to test the pH of various household solutions.

Credits

Sara Agee, Ph.D., Science Buddies

Cite This Page

MLA Style

Science Buddies Staff. "Cabbage Chemistry" Science Buddies. Science Buddies, 20 June 2014. Web. 16 Sep. 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p013.shtml>

APA Style

Science Buddies Staff. (2014, June 20). Cabbage Chemistry. Retrieved September 16, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p013.shtml

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Last edit date: 2014-06-20

Introduction

A solution is a mixture of a soluble chemical dissolved in water. Think about the difference between salt water and tap water. The salt in the salt water has dissolved and the solution looks clear, but the salt is still there and will taste salty if you taste it. Because solutions are made with water, which is made of hydrogen and water, the hydrogen in the water can make a solution into an acid or a base.

You might think about an acid as something that an evil villain uses to trap a super hero, but actually some very common household solutions are acids. Acids are solutions that will donate hydrogen ions in a solution, and usually taste sour. Some common acids are citrus fruit juices and household vinegar. Bases are solutions that accept hydrogen ions in solution, and usually feel slippery. Bases have many practical uses. "Antacids" like TUMS or Rolaids are used to reduce the acidity in your stomach. Other bases make useful household cleaning products.

How do you tell if something is an acid or a base? You use a chemical called an indicator, which changes in color depending on whether a solution is acidic or basic. Specifically, an indicator works by responding to the levels of hydrogen ions in a solution. There are many different types of indicators, some are liquids and some are concentrated on little strips of "litmus" paper. Indicators can be extracted from many different sources, including the pigment of many plants.

Red cabbage contains an indicator pigment molecule called flavin, which is one type of molecule called an anthocyanin. This water-soluble pigment is also found in apple skin, red onion skin, plums, poppies, blueberries, cornflowers, and grapes. Very acidic solutions will turn anthocyanin a red color. Neutral solutions result in a purplish color. Basic solutions appear in greenish-yellow. Therefore, it is possible to determine the pH of a solution based on the color it turns the anthocyanin pigments in red cabbage juice. The pH of a solution is a numerical measure of how basic or acidic it is. A solution with a pH between 5 and 7 is neutral, 8 or higher is a base, and 4 or lower is an acid. For more detailed information, consult the Science Buddies guide to Acids, Bases, & the pH Scale.

Video Project Idea Cabbage
Watch to learn more about why science is so important to our everyday lives and watch Science Buddies board member Courtney Corda, her son, and another mother-daughter team demonstrate how to put cabbage to work as a pH indicator.

Watch this video clip at http://abclocal.go.com/kgo/video?id=6867956 to learn more about why science is so important to our everyday lives and watch Science Buddies vice president Courtney Corda, her son, and another mother-daughter team demonstrate how to put cabbage to work as a pH indicator.

In this science experiment, you can extract your own cabbage juice indicator and use it to test the pH of different solutions around your home. You might be surprised to find out what common items around your house are acids or bases.

Terms and Concepts

  • Solution
  • Chemical
  • Acid
  • Base
  • Indicator
  • Pigment
  • pH

Bibliography

  • This web site at Chemistry 4 Kids has a great tutorial on chemistry, matter properties and mixtures. Go check it out:
    Rader, Andrew, 2005. "Rader's Chem4Kids." Andrew Rader Studios. 12/13/05.
    http://www.chem4kids.com/files/matter_intro.html
  • Here is a good website about acids and bases, including information about indicators with very nice pictures:
    Carboni, Giorgio, 2004. "Fun Science Gallery: Experiments with Acids and Bases." Pianoro, Italy. 12/13/05.
    http://www.funsci.com/fun3_en/acids/acids.htm
  • Cobb, Vikki, 1972. "Science Experiments You Can Eat." Harper Collins, New York, NY. 12/13/05

Materials and Equipment

  • Cabbage
  • Boiling pot of water
  • Strainer
  • Small white Dixie cups
  • Medicine dropper
  • A series of household items to test the pH of:
    • Fruit juice: lemon, lime, orange, apple
    • Soda pop (dark sodas might be tricky to see)
    • Vinegar
    • Baking soda solution
    • Cleaning products. Note: Always use caution when handling cleaning products.
    • Anything you want!

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Experimental Procedure

  1. Grate a small red cabbage and place the pieces into a glass bowl.
  2. Pour boiling water into the bowl to just cover the cabbage.
  3. Leave the cabbage mixture steeping until the liquid is room temperature. The liquid should be red in color.
  4. Place a strainer over a collection bowl and pour the mixture through the strainer to remove the pieces of cabbage.
  5. Now you should have a clear liquid that will either be purple or blue in color. The color of the liquid will change depending upon the pH. Use Table 1, below, to figure out the pH of the liquid by observing the color.
pH Color
2 Red
4 Purple
6 Violet
8 Blue
10 Blue-green
12 Greenish-yellow
Table 1. This data table shows what the pH of the liquid should be based on its color.
  1. Set aside your indicator solution. You will use it as your "stock" solution for your experiments.
  2. Next you will test various household solutions with your indicator. Use a separate Dixie cup for each solution you want to test because you do not want to mix chemicals that do not go well together or contaminate your results.
  3. Fill about half of the Dixie cup with your cabbage indicator solution. You can use less indicator solution for each cup if you do not have a lot of indicator solution.
  4. Add drops of a liquid you want to test until you see the solution change in color. Gently swirl the cup as you add the drops, being careful not to spill the solution.
  5. Record the pH and a description of the each solution in a data table in your lab notebook like Table 2 below.
  6. Analyze your results. How does the pH of the different household items you tested compare to each other? Are you surprised by any of your results?
Item Color pH
Lemon Juice   
7-UP   
Add liquids to the table as you test them   
Table 2. You can write down your observations and results in your lab notebook in a table like this one.

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Variations

  • There are other plants that can be used to make pH indicators as well: red onion, apple skins, blueberries, grape skins, and plums. Experiment with different sources of pigment, to see which produce the best indicators.
  • Can you use your pH indicator to conduct other useful experiments? What about testing the acidity of rain on a smoggy day? Or the usefulness of various antacid brands in reducing acidity of a solution?
  • You can use an indicator to write secret messages. Just use full strength lemon juice to write an invisible message on paper and let the message dry. To reveal the message, paint indicator over the paper with a paint brush.
  • You can actually buy pH strips that tell you the pH of a solution. How accurate is the pH indicator you made using cabbage compared to store-bought pH strips? You can purchase pH strips from aquarium stores or an online vendor such as Amazon.

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I did this project I Did This Project! Please log in and let us know how things went.

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