Wednesday, July 13, 2011

The Acid Test

With the boys home for summer vacation, we've been doing science projects nearly every day. Last night, we had a great time making an acid/base indicator from red cabbage juice. (So technically, this post should be titled "The Ph Test, but...)

The project I'm going to share with you today is super simple. So if your kids are itching for something to do, you might try it.

Directions for Making Red Cabbage Juice Indicator

Take 1/4 head of red cabbage and chop it up. Put the cabbage in a blender and add enough water to cover the cabbage. Puree the cabbage, and then strain it through a sieve. Save the juice. You can toss the pulp into your compost bin if you have one.

That's it! Now for the fun part!

What to Do with the Indicator?

Red cabbage juice contains anthocyanins (that's what gives it its color), which are sensitive to the presence of acids and bases. Acids turn the anthocyanins pink/red. Bases turn them blue/green. The anthocyanins stay purple in neutral solutions.

Once you have your cabbage juice indicator, your kids can pour about 1/4 cup of it into a number of glasses or jars. Then they can try adding small amounts of various substances to the indicator to see if it changes color. What you test is completely up to you. Some suggestions:
  • Soda pop
  • Vinegar
  • Lemon juice
  • Ammonia (WARNING: This is spectacular, but please, use ammonia in a well-ventilated area with adult supervision.)
  • Various juices
  • Milk
  • Wine
  • Seltzer
  • Antacids (Guess what color that will turn?! ;-)
  • Cream of tartar
  • Dish soap
  • Baking soda
  • Baking powder
  • Washing soda
If you measure your indicator and additions carefully (instead of dumping them in willy-nilly like we did), you can compare and contrast the color in the different glasses to see which of the additions were more acidic/basic than other.

Also, once you figure out which substances are acidic and which are basic, you might even try adding an acid to your red cabbage indicator, then a base, and then another acid for a real color-changing show!

Making Your Own Litmus Paper

For additional portability, you can make your own litmus paper by soaking a coffee filter in the red cabbage juice until it takes on a nice purple color. Then remove the filter from the juice and set it aside to dry flat. Once it's dry, cut it into strips. Now all your kids have to do it is dunk the strips for a second and then wait a few more seconds to see if the color changes. 

If you try this, I hope you have a great time! Who knows, your kids may fist pump and exclaim (as my five-year-old did), "Yeeesssss! We have a cabbage for science!"


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