The Difference Between Acids and Bases Using Different Indicators

Lejon Ross                     Betsy Ross Elementary School
                               6059 South Wabash
                               Chicago IL 60637
                               (312)535-0650

Objectives:

     This mini-teach is designed for the upper grade level; namely the seventh 
and eight grades.
     1.  To identify and distinguish acids and bases.
     2.  To identify the differences between acids and bases using litmus paper,
         pH paper and indicator solution.

Materials Needed:

Indicator Solution                            
Bowl                                          
Blueberries                                   
Isopropyl alcohol (rubbing alcohol)            
                                              
For experiment                                
AT FOUR WORKSTATIONS:                         
Cups                                          Baking Soda
droppers (10)                                 Distilled Water
Red or Blue Litmus paper                      Bathroom Cleaner
pH paper                                      Small clear jars (12)
Tap Water                                     Lemon juice
Vinegar                                       Sprite
Liquid detergent                              Ammonia 
Acetone (finger polish remover)

Strategy:

Making Indicator Solution
1.  Obtain a clean bowl and add one pint of blueberries.
2.  Add one bottle of rubbing alcohol and let stand for 24 hours.
3.  After 24 hours, drain solution into another clean container.

Procedure
1.  Test tap water, lemon juice, vinegar, sprite and liquid detergent with
    red or blue litmus paper (have students record results).
     Ask questions such as:
          a.  What color does litmus paper turn when it is a base?  (blue)
          b.  What color does litmus paper turn when it is a acid?  (red)
          c.  What are acids?  (All acids contain hydrogen and they burn)
          d.  What are bases?  (Bases contain negatively charged ions called
              hydroxide ions.  They are slippery to touch.)
2.  Test tap water, lemon juice, vinegar, sprite and liquid detergent with 
    pH paper (have students record number of reading)
      Question
          a.  With pH paper, how can you figure out what is an acid or a base?
              (Acids have a pH below 7, Bases have a pH above 7 and distilled
               water has a reading of 7 because it is neutral.)

Testing with indicator
1.  Add 5 drops of tap water to a clear jar.
2.  Add 5 drops of indicator solution to the jar also.
3.  Swirl solution around and record results.
4.  Repeat steps 1 through 3 with lemon juice, vinegar, sprite and liquid 
    detergent.  
5.  Try this same procedure with ammonia, acetone, baking soda solution (baking 
    soda and water) and bathroom cleaner and label them unknown A through E and 
    let the students figure out which one's are acids and which one's are bases. 
*Note*
Acids turns red and pink in the indicator solution.  Bases turns green in the
indicator solution. 

Performance Assessment:

The students will be able to determine on their own how to classify acids and  
bases using litmus paper, pH paper and indicator solution.  Students will be 
asked questions throughout the experiment to assess what is being learned. 

References:

Hann, Judith.  How Science Works.  Pleasantville, New York,  Reader's 
     Digest Association, Inc., 1991.

VanCleave's, Janice.   Chemistry for Every Kid.  New York, John Wiley
     & Sons, Inc., 1989.