Red Cabbage Chemistry
Ahh, the sweet smell of science! Invite your friends over to share in this super smelly but really cool activity. Plug your nose and get ready to make your own red cabbage indicator that will test the acidity or alkalinity of certain liquids.
- Red cabbage**
- Clear graduated cylinders or glasses
- White paper
- Apron or lab coat (avoid nasty stains!)
- Test chemicals: Vinegar, Baking soda, Lemon juice, Washing soda, Laundry detergent, Soda pop, Alka-Seltzer
Peel off six big cabbage leaves and put them in a blender with 12 cups of water. Liquify!
Depending on how much Red Cabbage Indicator you want to make use the optimum ratio of one cabbage leaf to two cups of water.
- Pour the purplish cabbage liquid through a strainer to filter out all of the big chunks of cabbage. Doesn’t cabbage juice smell great? Save the liquid for the experiments to follow.
- Set out three graduated cylinders or glasses, side by side. Fill each container half full with cabbage juice.
- Since you know that vinegar is an example of an acid, add a little vinegar to the first glass of cabbage juice. Stir with a spoon and notice the color change to red, which indicates that vinegar is classified as an acid.
- In the second glass add a teaspoon of washing soda or laundry detergent. Notice how the liquid turns green, indicating that this chemical is a base. Keep these two glasses of red and green liquid for future reference.
- Try adding other “test chemicals" to a small amount of cabbage juice and note the color change to determine if the chemical is an acid or a base.
Take It Further!
Use your cabbage juice indicator to test the acid or base properties of other common substances. You might want to try orange juice, lemonade, milk, salt, ammonia, or soap.
Try soaking some filter paper in concentrated cabbage juice. Remove the paper from the cabbage juice and hang it up by a clothespin to dry. Cut the dried paper into thin strips. Dip the strips into various liquids to test their pH. The redder the strip turns, the more acidic the liquid is. The greener the strip turns, the more basic the liquid is.
How Does It Work?
Some substances are classified as either an acid or a base. Think of acids and bases as opposites - acids have a low pH and bases have a high pH. For reference, water (a neutral) has a pH of 7 on a scale of 0-14. Scientists can tell if a substance is an acid or a base by means of an indicator. An indicator is typically a chemical that changes color if it comes in contact with an acid or a base.
As you can see, the purple cabbage juice turns red when it is mixed with something acidic and turns green when it mixes with something basic. Red cabbage juice is considered to be an indicator because it shows us something about the chemical composition of other substances.
What is it about cabbage that causes this to happen? Red cabbage contains a water-soluble pigment called anthocyanin that changes color when it is mixed with an acid or a base. The pigment turns red in acidic environments with a pH less than 7 and the pigment turns bluish-green in alkaline (basic) environments with a pH greater than 7.
Red cabbage is just one of many indicators that are available to scientists. Some indicators start out colorless and turn blue or pink, for example, when they mix with a base. If there is no color change at all, the substance that you are testing is probably neutral, just like water.
Science Fair Connection:
Red Cabbage Chemistry could be a great science fair project. Once you have tested the various chemicals and household substances listed above and have a clear understanding of acids and bases, you could make a few changes, run some new tests, and make some comparisons.
- Try testing a variety of beverages to see which ones are the most acidic. Some people think Starbucks coffee is very acidic. Could you use the red cabbage juice and the process described above to run some tests of different brands of coffee to see if those claims are true?
- What happens when you put pieces of acid-reducing medication in acidic liquids? Choose one acidic liquid and test different brands of acid reducers to see which ones are the most effective. Just make sure you use the same "dosage" of acid reducer and the same form of acid reducer (liquid vs tablet) and the same amount and type of acidic liquid so that your tests are fair and your conditions are standardized as much as possible.
- Is a liquid or a tablet acid reducer more effective? Use the same brand and the same "dosage" of medication and put it in the same amount and type of acidic liquid. The only variable you're testing is the difference between the liquid and the tablet medication. Do they both work? Does one work more quickly to reduce the acid?
Be sure that you only change one variable at a time, make your comparisons, and document your results. Who knew that such a simple kitchen chemistry demonstration could have such real world applications? Many adults at the science fair will be glad to know the results of your research!
- Reds Cabbage Chemistry Review by Shatira Johnson
This project look cool I want to know how you did this project.
(Posted on December 11, 2009)
- Fun for all ages Review by Cathy Duynisveld
I did this with a group of elementary kids as an after school science project. They enjoyed the science part and loved to nibble on the extra cabbage. I plan to do this with a high school science class just to get them thinking and maybe a bit excited. Yes, it will fit nicely into the course.
(Posted on September 14, 2012)