A Chemical Reaction
Take a few leaves of "red" cabbage and boil them in about 2 cups of water. When it comes to a good boil, turn it off and let it cool. Using a funnel fill a large balloon with baking soda (about 2 Tablespoons).
Put about 3/4 cup of white vinegar in an empty 2-liter bottle.
Pour about 1/2 cup of the cooled "red" cabbage juice in the 2-liter bottle with the vinegar (leave the leaves out). The vinegar should change the color of the cabbage juice from purple to pink or red.
Slip the balloon's neck over the 2-liter's neck without dropping in the baking soda as much as you can. When you are ready, dump the baking soda into the bottle by lifting the balloon.
The chemical reaction between the baking soda and the vinegar creates carbon dioxide and water. The carbon dioxide inflates the balloon and the neutralizing of the vinegar's acid changes the cabbage juice's color from pink back to purple...
and then to blue.
The baking soda then turns the liquid to a base, and turns the cabbage juice to a blue color.
The anthocyanin in the cabbage makes it an acid/base indicator.
Put about 3/4 cup of white vinegar in an empty 2-liter bottle.
Pour about 1/2 cup of the cooled "red" cabbage juice in the 2-liter bottle with the vinegar (leave the leaves out). The vinegar should change the color of the cabbage juice from purple to pink or red.Slip the balloon's neck over the 2-liter's neck without dropping in the baking soda as much as you can. When you are ready, dump the baking soda into the bottle by lifting the balloon.
The chemical reaction between the baking soda and the vinegar creates carbon dioxide and water. The carbon dioxide inflates the balloon and the neutralizing of the vinegar's acid changes the cabbage juice's color from pink back to purple...
 |
| The photo makes it look more purple than it actually did. |
and then to blue.
The baking soda then turns the liquid to a base, and turns the cabbage juice to a blue color.
The anthocyanin in the cabbage makes it an acid/base indicator.
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.
