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An “Edible Slime” alginate polymer is mixed up here from brown seaweed

Subject:

Science  

Grades:

4, 5, 6, 7, 8  

Title – Edible Slime – the Polymer You Can Eat!
By – Robert Ellingson
Primary Subject – Science
Grade Level – 4-8

Introduction:

    In this activity, the students will be learning that nature produces polymers like alginate from brown seaweed. They learn that sodium alginate plus Ca2+ ions makes a slime that is edible.

Materials Needed:

      Per 2-6 students:

        Clean cup of water

        Sodium aginate (

available at Atlas Chemical in S.D.

        )

        Calcium acetate or calcium chloride

        Pipette or straw for transferring dissolved calcium acetate

        4 – 5 oz. Salsa cup or a Dixie cup for the alginate solution

        Small 1 – 2 oz. cup for the calcium solution

        Kool-Aid for flavor

    Per student:

      Craft sticks for scooping and stirring and eating

Background Information:

    The word polymer means “many – units”. These are long molecules made by linking many small molecules called monomers together. Protein is a good example. It is made by linking many amino acids together. Also all plastics are polymers. For example, the most plastic cups are made from polystyrene, which is made by linking many styrene units together.

Introduction:

      Show the students an example of what they will be making and eating by adding some pre-made calcium acetate solution to some pre-made sodium alginate solution. Use the two sticks to pull up the slime. Add some Kool-Aid and eat it. This will give them a reference to what you are about to talk about.
      On the board, the teacher reads with the students the following:

      The polymer that we will be eating is formed by mixing two chemicals: sodium alginate and calcium acetate. The alginate comes from brown seaweed (kelp). The alginate is a polymer because it is made from many units of glucose (a type of sugar).

    When we add dissolved calcium acetate to dissolved sodium alginate we get a new substance called calcium alginate, which does not dissolve in water, thus forming a gel, a slime, an edible slime.

Student Activity Procedure: With each step, first demo the activity; then let the students do it.

      Part One (The Sodium Alginate Solution)

        1. Using a marked craft stick, add 4 scoops of sodium alginate to the large salsa cup.

        2. Put 7 squirts of water to the cup.

        3. Stir for about 3 minutes.

      Part Two (The Calcium Acetate Solution)

        1. Using the other craft stick, add one small scoop of calcium acetate to the little salsa cup.

        2. Put two squirts of water.

        3. Stir until dissolved.

        4. Go back to stirring the sodium alginate.

      Part Three (The Slime)

        1. Add about 12 drops to calcium acetate to the sodium alginate.

        2. Use the two sticks to try to pull the slime out of the cup.

        3. Add more drops if necessary and stir.

Teacher adds a scoop of Kool-Aid. Students stir and eat with the two sticks. Conclusion:

      Questions and Answers
      1. What do we call long molecules that are formed by linking many units (smaller molecules) together?

Polymers

      2. What organism makes alginate?

Brown seaweed or kelp

      3. What ion is needed to turn sodium alginate into slime?

Calcium ion Ca2+

      4. What happens to sodium alginate and calcium acetate when water is added to them?

They dissolve.

      5. What is the chemical name of our slime?

Calcium Alginate

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