Can a Cabbage Distinguish an Acid from a Base? Mark as Favorite (5 Favorites)
In this lab, students will determine what colors the cabbage indicator turns in acidic, neutral, and basic solutions. Students will then analyze household materials To determine if they are acid, base, or neutral.
Elementary, middle, or high school
By the end of this lesson, students should be able to
- Use red cabbage indicator to detect acid, neutral, or base properties of a solution.
- Understand the acid base pH scale.
This lesson supports students’ understanding of
- Acids and bases
Teacher Preparation: 60 minutes
Lesson: 45 to 60 minutes
- Red cabbage indicator (See Teacher Notes)
- Dropper bottles
- Small plastic cups
- Solutions that are acid, neutral, or base (See Teacher Notes)
- Household items which are acidic, basic, and neutral (See Teacher Notes)
- Crayons or colored pencils
Always wear safety goggles when working with chemicals.
Preparing Red Cabbage indicator Solution:
Students can prepare red cabbage indicator solution in their groups.
- Give each group two or three leaves from a red cabbage.
- Have students tear up the leaves and place them in a zip closing plastic bag.
- Add about 1 cup of room temperature water to the bag.
- Get as much air out as possible and close the bag securely.
- Squeeze and squish the bag until the water in the bag turns a dark blue. This is the red cabbage indicator solution.
- Open a corner of the bag and carefully pour the indicator solution into a clean cup. Students will use portions of this indicator to test the different solutions you’ve prepared.
Preparing the acid, base, and neutral solutions:
- Acidic solutions: Use either vinegar or lemon juice in separate labeled cups for each group. Place a dropper in the cup.
- Basic Solutions: Dissolve baking soda in water, or powdered laundry detergent in water and place in separate labeled cups for each group. Place a dropper in the cup.
- Neutral solution: Water in a cup for each group. Place a dropper in the cup.
For the Student
You will make a special solution called an acid-base indicator from red cabbage leaves. You will then use the red cabbage indicator solution to test solutions to find out whether they are acid, base, or neutral. Then you will use your observations to classify some common household items as acid, neutral, or base.
Red cabbage contains a pigment molecule known as an anthocyanin. This same pigment gives many other items in nature a bright red color. Apples, plums, poppies, grapes, cornflowers, and red maple leaves in the fall all contain anthocyanins. When you use the indicator to test a substance, the color you see will indicate whether the substance being tested is an acid, base, or a neutral substance. There is scale or way to measure how acidic or basic a substance is. This is called the pH scale. The scale goes from 1 -14. One is the most acidic and 14 is the most basic. A substance which is neither an acid or a base, but is neutral, has a pH of 7.
If the pH is lower than 7, it is acidic. If it is higher than 7, it is basic. The further the pH is from 7, the more acidic or basic the substance is. The human stomach has a pH of 1–2 because hydrochloric acid is produced by cells in the stomach lining. Acid is important in stomachs because it helps break down food.
When working with chemicals, it is necessary to work carefully and to wear an apron and goggles.
You will test solutions that are acidic, neutral, or basic. You will use this information to determine whether certain household substances are acid, base, or neutral.
Have crayons or colored pencils handy to color in the rounded-cornered rectangles in each row of the table under the color heading. You will use droppers and and small cups to test each solution or substance with red cabbage indicator.
|Laundry Detergent Solution|
|Baking Soda Solution|
Now test some household substances to identify them as acidic, neutral, or basic.
|Substance||Color||Acid, Neutral, or Base||pH estimate|
|Cream of Tartar|
|Clear colorless soda like sprite or 7-Up|
- What did you learn from this experiment?
- Did anything surprise you?
- From this experience, how can you identify an acid from a base?