ACIDS AND BASES

Objective:  Students will use indicators to determine whether a substance is an acid or base.
Preparation:   The teacher may do a grade appropriate lesson on pH.  It is enough for purposes of this lesson that the students understand that dissolved materials change water molecules to form an acid or a base.

Procedure:  Introduce by explaining that indicators are special solutions that change colors when they are acted upon by another substance and that they are used to identify acids and bases.
Each group of students should have a set of cups containing a selection of acids and bases to be tested.  Depending on the age and ability of the students, the teacher may choose to prepare these ahead of time.  Students will use a dropper  to squeeze cabbage juice, record the color change, and record the result.
Materials:
          1.RED CABBAGE JUICE INDICATOR:  Soak a cup of shredded red cabbage in very hot water for at least one hour or until the water is a deep purple.  You can also boil the cabbage for 15 minutes and drain off the water. Separate the puple water from the cabbage with a strainer and use the water as an indicator.
           Note:  When acid is added, the cabbage juice will turn bright pink.  When a base is added, it will turn green.
           2.  LIQUIDS TO BE TESTED:
                               Acids:  Choose from:  Lemon juice, white vinegar, boric acid, 7-Up (or similar commercial colorless soda pop), dissolved vitamin C tablet.
                               Bases:  Baking soda, Alka Seltzer, amonia, washing soda, saturated borax solution, liquid soap, liquid dish detergent
           3.  DROPPERS
4. CUPS
           5.  pH TEST PAPER

Follow-up:  Discusssion of results.  Teacher shows pH test paper and explains that it works much the same as the cabbage juice indicator and that it will be used to in the collaborative activity to test water.