The Sodium Alginate Polymer Chemistry Demonstration Kit shows what happens when long polymer chains are “tied together” via cross-linking. Be forewarned, students may insist on “replaying” this demo many times.
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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, semisolid 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 “replaying” this demonstration many times. That’s OK, because the polymer is a nontoxic food additive!
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.
Correlation to Next Generation Science Standards (NGSS)
Science & Engineering Practices
Analyzing and interpreting data
Constructing explanations and designing solutions
Planning and carrying out investigations
Disciplinary Core Ideas
MS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
HS-PS1.B: Chemical Reactions
HS-PS1.A: Structure and Properties of Matter
HS-PS2.B: Types of Interactions
MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
HS-PS1-2. Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
HS-PS1-3. Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.