Sodium Alginate Polymer - Chemical Demonstration Kit

By: The Flinn Staff


Sodium alginate is a natural “gummy-worm” polymer obtained from giant kelp and seaweed. The polymer is extremely hydrophilic or “water-loving” and dissolves in water to form a thick, viscous, smooth gel—perfect for use as a thickening agent in ice cream, yogurt, and other dairy products. Reacting sodium alginate solution with calcium or copper ions produces a smooth, flexible, semi-solid substance that precipitates from water in the form of—worms! The “worms” have the same texture and consistency as gummy candy. This fascinating demonstration shows what happens when long polymer chains are “tied together” via cross-linking. Be forewarned, your students may insist on “re-playing” this demonstration many times. That's OK, because the polymer is a nontoxic food additive! Enough chemicals are provided to perform the demonstration as written seven times.

Concepts: Polymers, polymer gels, cross-linking, polysaccharides.
Time Required: 15 minutes
Materials Provided: Calcium chloride solution, copper(II) chloride solution, sodium alginate, sodium chloride solution, jumbo pipets.