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Insta-worms

Students become polymer chemists who will make gelatinous worms.

Polysaccharides are polymers that are made by linking hundreds of glucose molecules. This activity uses sodium alginate, a polysaccharide polymer isolated from seaweed. The monomer glucose is sweet and dissolves easily in water but the polymer starch is not sweet and forms a thick, sticky paste in solution.

In this activity, the sodium alginate immediately changes from a liquid to a solid when it contacts the calcium chloride solution. The calcium (Ca++) ions replace the sodium (Na+) ions and link the polymer chains together — much like the rungs of a ladder link the two sides. The result does not dissloves (is insoluble) in the calcium chloride solution. The squishy stuff inside the ''worms'' is unreacted sodium alginate. If you leave the worm in the solution longer, more calcium ions will react and the worm's ''skin'' will get thicker.

Objectives

  • Name some practical uses for polymers.

  • Describe in general terms what occurs during a polymerization reaction.

  • Investigate the properties of common polymers.

Materials

  • Per Pair or small Group:
    powdered calcium chloride
    sodium alginate solution or Gaviscon®
    water
    cups
    squirt bottles for the sodium alginate solution
    plastic baggies for each student

    *Sodium alginate solution is available in pharmacies. An alternative is to use Gaviscon®, a heartburn remedy that has sodium alginate as a primary ingredient.

    Teachers’ Source and Steve Spangler Science  sell a complete ‘’worm kit’’.

Key Questions

  • How was the “worm” created?
  • Which chemical is polymerizing in this reaction?
  • Does your worm look similar or different to your partners’? Explain.
  • Could these chemicals be useful in creating any other sort of polymers?
  • Where is the substance starch found? In what? What do we use starch for?

What To Do

Preparation:

  1. Make the calcium chloride solution: For each group of students, start with ¾ of a cup of warm water into a cup. Add a teaspoon of calcium chloride powder and stir with a spoon until most of the powder dissolves.
  2. Set up stations for each group of students. Make sure that each station has:
  • Calcium chloride solution in a cup
  • Sodium alginate solution in a squirt bottle
  • Cups
  • Plastic sandwich bags (one per student)

Instructions (You may want to do a demonstration first):

  1. A small group (2–4) of students can share a cup of calcium chloride solution. Each student can make their own ‘’worm’’.
  2. Squirt a small stream of the sodium alginate solution into the cup containing the calcium chloride solution.
  3. Carefully pull the “worm” out of the calcium chloride solution with their hands. If the worm breaks, the gooey end can go back into the calcium chloride solution to seal it up.
  4. Store the ‘’worm’’ in a sandwich bag.
  5. Wash excess calcium chloride solution down the sink.

Extensions

  • What happens if you use more or less calcium chloride powder when making the CaCl2 solution? Do your worms still form?
  • Make colourful worms by adding food colouring to the sodium alginate.

Other Resources

University of Southern Mississippi | Polymer Science Learning Center | Make a Virtual Polymer