How to Make Red Cabbage pH Indicator (without stinking up the kitchen!)


Red cabbage makes a great pH indicator, but making it by boiling it on the stove for the juice can make the house smell like, well, cabbage, which for most, is an unpleasant smell.
source
There is an easier way, and, surprisingly, it produces more juice than the boiling method.
  1. Take about 1/3-1/2 of a small red cabbage and slice it into large shreds.
  2. Put the cabbage shreds into a blender.
  3. Add about 2 cups of boiling water.
  4. Turn on your blender and blend until you have a mush (yes, mush is a scientific term on this blog.)
  5. Put a strainer over a bowl. Pour the mush into the strainer, straining out the juice.
  6. Now you can  use this red cabbage juice as an indicator. Acids will turn the pigments in the indicator to a reddish color; bases will turn the pigments bluish or yellow-green.
How to Make Litmus Paper with Red Cabbage Juice

  1. Cut strips from plain white paper towels about an inch wide and a couple inches long.
  2. Take the paper towel strips and soak them in the cabbage juice for about a minute. Remove them and let them dry on something that won’t stain.
  3. Let the paper strips dry and as soon as they are dry your litmus paper is ready to use.
Sources:
GEMS: Of Cabbages and Chemistry
Grades 4-8
4 Sessions
88 pages

Students explore acids and bases using the special indicator properties of red cabbage juice. The color-change game Presto Change-O helps students discover the acid-neutral-base continuum. They learn that chemicals can be grouped by behaviors, and relate acids and bases to their own daily experience. An “Acid and Aliens from Outer Space” extension activity can be presented to reinforce student learning or as an assessment. The unit is an excellent lead-in to the GEMS guide Acid Rain.

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