Red Cabbage Lab: Acids and Bases
Introduction:
Liquids all around us have either acidic or basic (alkaline) properties. For example, acids
taste sour; while bases taste bitter and feel slippery. However, both strong acids and strong bases
can be very dangerous and burn your skin, so it is important to be very careful when using such
chemicals. In order to measure how acidic or basic a liquid is, one must use the pH scale as
illustrated below:
The strength of the pH scale is determined by the concentration of hydrogen ions (H+) where a
high concentration of H+ ions indicate a low pH and a high concentration of OH- ions indicate a
high pH. The pH scale ranges from 1 to 14 where 1 to 6 is classified as acidic, 7 is neutral, and 8
to 14 is classified as basic.
In this lab, you will use the juice from red cabbage as a pH indicator to test common household
liquids and determine their pH levels. You will mix cabbage juice with different household
liquids and see a color change produced by a pigment called flavin in the red cabbage. Through
this color change, you will be able to successfully identify the approximate pH of common
household liquids using the table below:
Color
Pink
Dark Red
Violet
Blue
BlueGreen
GreenYellow
Approximate
pH
1-2
3-4
5-7
8
9 – 10
11 - 12
Acid/Base
Acid
Acid
Acid/Neutral
Base
Base
Base
Materials:
1. Small Beaker or Cup
2. Beaker or Cup of Red Cabbage Juice Indicator
3. Micropipettes
4. White Vinegar
5. Lemon Soda
6. Coca Cola
7. Bleach
8. Ammonia
9. Baking Soda
10. Shampoo
Pre-Lab Predictions:
Look at each of the liquids being tested. Predict whether each of the substances is acidic,
neutral, or basic. Circle one.
White Vinegar
Acidic
Neutral
Basic
Lemon Soda
Acidic
Neutral
Basic
Coca Cola
Acidic
Neutral
Basic
Bleach
Acidic
Neutral
Basic
Ammonia
Acidic
Neutral
Basic
Baking Soda
Acidic
Neutral
Basic
Shampoo
Acidic
Neutral
Basic
Procedure:
1. Use a sharpie to label each of the Dixie Cups with the liquid that it will contain.
2. Send one member of your lab group to the supplies table with the labeled Dixie cups.
Add 2 pipettes of the solution to its corresponding cup. This may take more than one
trip!
3. Once all of the cups are back at your lab table. Add one pipette of red cabbage juice to
the cups one by one. Observe and record any color change in the data table below.
Data:
Table 1: pH of Household Solutions
Household Solution
Color Change
Predicted pH
Actual pH
White Vinegar
5.0
Lemon Soda
3.4
Coca Cola
2.8
Bleach
12.0
Ammonia
11.6
Baking Soda
10.0
Shampoo
6.5
Table 2: Categorize your results below
Strong Acids
Weak Acids
Neutral
Weak Bases
Strong Bases
Follow-Up Questions:
1.) Were the pH’s predicted by the red cabbage juice indicator close to the actual pH of the
solution? How accurate is red cabbage juice as an acid/base indicator?
2.) Of the solutions tested, which solution would have the greatest concentration of hydrogen
ions? What about hydroxide ions?
3.) What defines an acid, base, or neutral substance?
4.) Whenever you mix an acid with a base, they neutralize each other. If this is the case, why is
Alka-Seltzer used to treat stomach aches? (Note: excess stomach acids cause stomach aches)
5.) What is acid rain and how is it a problem to oceans, rivers, lakes, ponds, etc.?
6.) Knowing what you know about acid rain and acid/base chemistry, think of and describe a
working scientific solution to the corrosion caused by acid rain.