Substantive Education

March 15, 2010

Red Cabbage as Litmus Paper

Red cabbage is a wonderful vegetable, and not just for coleslaw.  It can also be used as an indicator in science experiments.  Currently I’m teaching a high school Chemistry class and the module we looked at today dealt with with acids and bases.  We discussed the intricacies of hydrogen gaining or losing an ion and why that produces a base, along with …well, that doesn’t matter here.

Back to the wonders of the cabbage.Most experiments involving acids and bases require you to purchase litmus paper.  Litmus paper is an ‘indicator’ and changes color when it is exposed to an acid or base.  Anyone with a pool is probably familiar with the concept.  I didn’t have any litmus paper, and seeing as how we live in the country and a trip to a school supply store is a bit of a drive, I frequently use my good friend, the red cabbage.  Here is how to use your cabbage as an indicator in your science experiment.

Chop up a section and put it into a saucepan on the stove.  Allow the cabbage to come to a boil for 5 to 10 minutes.  You now have an indicator.  Using a ladle, scoop some of the liquid (avoiding the actual cabbage) into clear glasses or jars.  You only need a little.  You are ready to test away.

This is the color of the plain cabbage juice, our indicator

We added lemon juice to the glass on the left, the glass to right has nothing added.

The glass on the left after lemon juice was added.

Collect a variety of household items and chemicals and add a few drop to your glass.  If the indicator turns red  you have added an acid, if your indicator turns green you have a base.  We tested lemon juice, ammonia, lime away, windex, coke, and saliva.  Obviously no change in color indicates a neutral substance.   Once kids get the concept they start wanting to test everything…hence the saliva…which turned out to be neuteral.

The center glass has just had amonia added.

The center glass has just had ammonia added.

Coincidently, I just covered similar material, at an easier level,  with my elementary school science class and they loved the mixing and dramatic color changes…enough that several students went home and asked their moms to buy some cabbage so they could continue to explore.  What more could a teacher ask for?


1 Comment »

  1. i found this very helpful and it came in handy with my science project !!!! Thankyou !

    Comment by Maygen — December 13, 2011 @ 4:24 pm | Reply

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