Red Cabbage Litmus Paper (or Play with your Food and Eat it too!)

With St. Patrick’s Day right around the corner, I thought that this would be a fun project and that people might already have cabbage on their grocery lists for the Irish holiday. 

All you will need is a head of red cabbage and some paper towels.  Alternately, you can just use the juice from canned red cabbage.  I recommend having your child wear an old tee shirt or a home-made lab coat, since I’m guessing that cabbage juice will stain.   To make a lab coat, just have your child write their name in permanent marker on the pocket of a man’s old button-down shirt.  They’ll love it! 

Chop half a head of red cabbage into small pieces and add it to a pan with about a cup of water.  Boil the cabbage uncovered for about 15 minutes, stirring occasionally, let it cool, and strain the juice into a jar or bowl.  (Save the cooked cabbage for your favorite recipe and make cole slaw with the other half!)

Have your child cut the paper towels into strips about an inch wide and a few inches long and soak them in the cabbage juice for about a minute.  Remove them and let them dry on something that won’t stain.  I blotted them a little to speed up the drying process.  You might even try using a blow dryer!

When dry, your litmus paper will be ready to use for testing acidity.  Your child can dip the paper into orange juice, soapy water, lemon juice, baking soda in water, baking powder in water, vinegar, and anything else they want to test.  The paper will turn red-pink in acids and blue or green in bases.  Even very young children will enjoy watching the color change!  The colors we saw were amazing.  I think the kids may make a collage with their litmus paper when it dries.  You can also have them tape a strip or two of the paper into their lab notebooks.

If they ask what an acid is, you can first tell your child that everything in our world is made of very tiny pieces called atoms.  Atoms are so small that if you blow up a balloon, it will contain about a hundred billion billion atoms of the gases that make up air.  Atoms are often bonded to other atoms to form a group of linked atoms called a molecule.  A water molecule, for example, has two hydrogen atoms and one oxygen atom, bonded together. 

Then, explain that acids are substances that usually dissolve in water to form free-floating hydrogen atoms.  Bases are the opposite and take up free hydrogen atoms.  The molecules in the cabbage juice litmus paper change when exposed to an acid or base, making the paper change color. 

Now I know why my mom’s delicious Pennsylvania Red Cabbage recipe turns red when we add the vinegar!

Tags: acids, bases, kids, litmus, paper, red cabbage, Science