Physical Science

Cabbage Chemistry - Lose the Indicator Blues

(Related lesson: Tin Can Ice Cream)

Content Objectives:
Students will be able to:

Know there are chemical and physical properties of matter (e.g., mass, volume hardness, density, reactions to simple chemical tests, level of acidity, level basicity).

Process Objectives:
Students will be able to:

Observe that substances can react to produce with other substance with different chemical and physical properties.

Assessment Strategies:
Questioning:

1.   What did you observe?

2.   How does it compare to control?

Teacher adds an amount of vinegar or detergent to two tablespoons of indicator solution. Students must discover the proper amount that was added by using what they have learned.

Writing response: Write their observations and how it compared to the control in steps four through seven.

Procedures:

1.   Make an indicator solution:

1. Tear up red cabbage leaf into small pieces.
2. Place the pieces in a zip-lock plastic bag.
3. Add three-fourths cup warm water and close bag tightly.
4. Squeeze the bag until the water turns dark blue (about three minutes).

2. Label your cups “vinegar,” “detergent” and “control” using tape and pen.
3. Open plastic bag. Use a tablespoon to place two tablespoons of indicator solution into each cup. Close bag for later.  
4. Use eye dropper to place one drop of vinegar in vinegar cup. Gently swirl.  Compare to control.
5. Use a toothpick to add small amount of detergent to the detergent cup. Gently swirl. Compare to control.
6. Use a toothpick to add tiny amount of detergent to the vinegar cup and swirl.  Compare to control. (If it ends up green, too much detergent was used.)
7. Add one drop vinegar to the detergent cup and swirl. Compare to control.  How close did you get?

Extensions:

1.   Add two tablespoons indicator solution in each cup. Add five drops of vinegar in one cup. Add five tiny scoops of detergent to the other cup. Use what you learned to change the colors in these two solutions back to blue.

2.   Add two tablespoons of indicator solution to one cup.  Have a partner add a “mystery amount” of vinegar or detergent (one to five drops). Find out how many drops your partner added by changing color back to blue.

Suggested Level:
Grades 5-7

Standard Category:
3.4  Physical Science, Chemistry and Physics

Materials:
Quantities of the following sufficient for each student:

Three-fourths cup warm water

One red cabbage leaf

Measuring spoons

Zip-lock bag

Eye dropper

Three small cups

Vinegar (one teaspoon)

Laundry detergent powder (one teaspoon)

One flat toothpick

Masking tape

Pen

Instructional Strategies:
Small group instruction

Use of manipulatives

Discovery learning