I. INTRODUCTION:
The use of simple easy to find chemicals can result in a dramatic demonstration
of production of a chemical foam. A variety of skills and topics can be
covered in this activity including: lab safety and behavior, wafting
to smell chemicals, observation skills, measurement and mathematics skills.
II. MATERIALS: Baking soda, alum, unflavored gelatin, vinegar, plastic
spoons, two plastic cups for each student, food coloring (optional).
III. PROCEDURES:This
activity is very good with a variety of ages depending on the amount of
structure the teacher uses.
a. Each student places one spoonful of each solid
into one of the cups (it can be labeled "1" or "solids").
To reinforce appropriate lab behavior and safety, be sure that different
spoons are used for each solid - although mixing them will not adversely
affect the results.
b. Each student will put three teaspoons of vinegar
in the "2" or "liquid" cup. If desired, some food coloring
can be added to the vinegar. Demonstrate how to waft the odor of
the vinegar toward the nose in order to safely smell the chemical.
c. Once the materials have been collected, place
the solids cup on several sheets of newspaper. To build the excitement,
have all the students mix their solids together well and wait to add the
liquids all at the same time. On the count of three, they may pour the
liquid into the solid cup and stir.
d. As the foam is produced and spills over the
sides, they may continue stirring. If the bubbles are not overly stirred,
they will last a long time. Once the reaction has stopped, the students
may want to start it again. Give them access to the chemicals and they
will realize that the addition of more vinegar will indeed restart the
reaction.
IV. FOLLOW UP ACTIVITIES:
Discussion of change of matter or materials
Descriptive paragraphs or list of adjectives
Why lab procedure is important to follow
Measurement and math can be used by having students
compare quantities of dry and liquid ingredients used in the production
of foam
Discussion of the chemistry of fire extinguishers
V. TEACHER NOTES:
All the ingredients can be found in a grocery store or drug store.
NOTE: A foam fire extinguisher is made from water, baking soda,
a strengthening agent (usually a protein [gelatin]), and an inner container
of alum. When mixed together, the foam last s for a long time due to the
protein which stabilizes the foam. This information can be used to show
students that chemicals combine to form useful materials in their lives.
Source: Liftig, Inez. "A Secret Foam-ula." Science
and Children . Vol 26, No. 4, January 1989, pp. 30-31.
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