An Introduction to Acids and Bases

Therese Tobecksen              Saint Andrew the Apostle
                               331 155th Place
                               Calumet City, Illinois 60409
                               708-862-4143

Objectives:

1.  Primary students will review the concept of sorting objects by various
    physical attributes.
2.  Students will sort Lego blocks by size, color, shape, number of "bumps",
    etc.
3.  Students will classify household liquids as bases or acids by using 
    cabbage-juice paper and then litmus paper.

Materials needed:

Assorted Lego blocks, a purple cabbage, cabbage-juice indicator paper (prepared 
at home by soaking half a cabbage in boiling water and then dipping and drying 
coffee filters), litmus paper, orange juice, vinegar, cola, liquid soap, baking 
soda in water, Pepto-Bismol and small plastic or paper cups.

Strategy:

Ask students how they could sort a collection of Lego blocks.  Discuss how to 
sort them by size, color, shape, etc.  Mention other items which are sorted such 
as: items in a grocery store, items in their desk, the animal classification 
system. 

Show a half head of purple cabbage.  Explain that the other half had been soaked 
in boiling water and that the juice it made was used to soak coffee filter 
papers which they will now use as a "sorter" or indicator. 

Reveal and identify household liquids which will be sorted.  Send students to 
lab stations which have been set up with cups containing about a quarter cup of 
the various liquids. 

Let the students try to discover that the cabbage indicator will turn green or 
pink.  Discuss some of the characteristics of acids and bases.  Try to have  
them conclude that green indicates a base and pink indicates an acid.  Repeat 
the procedure using litmus paper.                 

Discuss some everyday situations involving acids and bases such as the use of 
vinegar to clean a coffee pot or tea kettle, swimming pool chemicals, acid rain, 
etc.