WISE 2007-2008
Name: ____________________________________
Acids, Bases, and Indicators: A Colorful Activity!
Purpose: To label common household solutions as acidic or basic using cabbage juice and litmus paper.
Introduction:
Water molecules collide and produce H+ and OH- ions from the H2O compound. The hydrogen
ion, H+, is characteristic of an acidic solution, while the hydroxide ion, OH-, is characteristic of a basic
solution. Water is a neutral substance because the concentration of the two ions is equal. As solutes are
added to water to make solutions, however, the balance of H+ and OH- is changed.
+

H+ + OH- 
H2O
A measure of the hydrogen ion (H+) concentration is pH. Low values of pH indicate an acidic
solution (lots of H+). High values of pH indicate a basic solution (lots of OH-). Acids have a pH less
than 7, bases (or “alkaline” substances) have a pH greater than 7, and neutrals have a pH of 7.
Example
of a pH
scale
Each whole pH value below 7 is ten times more acidic than the next higher value! For example,
a pH of 3 is ten times more acidic than a pH of 4. For pH values above 7, each whole value is ten times
more basic than the next lower value! Acids taste sour while bases taste bitter and are slippery.
Changing the hydrogen ion concentration will cause some natural dies to change colors. Just as
the color of tea will change as lemon is added, red cabbage juice will have a different color in acids and
bases. Dyes which change color in response to the change of pH are called acid-base indicators.
WISE 2007-2008
Name: ____________________________________
Experiment:
The lab activity today will explore the use of red cabbage juice as a natural acid-base indicator.
In the test tube rack you will find an example of an acid, water (a neutral substance), and basic solution
with the cabbage juice added.
What is the color of cabbage juice in an acid? _____________________________________________
What is the color of cabbage juice in a base? ______________________________________________
What is the color of cabbage juice in water? _______________________________________________
Now put 10 drops of your first unknown sample into one well of the dropping tray and add 2 drops of
cabbage juice extract. Repeat this procedure with each sample.
Sample
Color With Cabbage Juice
Acid/Base/Neutral
Liquid soap
Sprite soda
Vinegar
Baking soda
Lemon juice
Sugar solution
Windex
Extension activity: Put your name on a piece of white paper on the table. Now using a Q-tip, dip into
the solutions and make an invisible design on your paper. Vary the acids and bases used on the paper in
order to create different colors. When the solutions have been absorbed, the paper will be sprayed with
cabbage juice to reveal your design!