Sodium Alginate Worms

Sodium alginate solution is extruded into a calcium chloride solution to create flexible “worms” as calcium ions crosslink the alginate chains. The rapid gelation lets you explore polymer formation, diffusion, and how soak time changes worm firmness.

1. Prepare two clear, labeled cups per participant: one with calcium chloride solution (about 2 to 3 percent in water) and one with sodium alginate solution (about 2 percent in water). Add a few drops of food coloring to the alginate if desired.
2. Provide each participant with goggles, nonlatex gloves, a clean syringe without a needle, and a fork or slotted spoon.
3. Fill the syringe with the colored sodium alginate solution, tap out air bubbles, and slowly dispense the stream into the calcium chloride cup to form long worms. Move the tip gently to control thickness and length.
4. Let the worms sit in the calcium chloride for 10 to 60 seconds. Shorter times give softer worms; longer times yield firmer worms.
5. Use the fork to lift the worms into a water rinse to remove excess calcium chloride, then handle and observe their texture.
6. Cut a worm and briefly dip the cut end back into calcium chloride to “heal” it, showing fast surface crosslinking.
7. Discuss observations and connect them to particle models of crosslinking and diffusion. Clean up according to venue rules.

Alginate Worms - Pueblo Science:

Sodium Alginate Worms - Imagination Station Toledo:

📄 Goo Worms - ACS: https://www.acs.org/education/activities/goo-worms.html

• Make “beads” by dripping alginate one drop at a time instead of a continuous stream.
• Compare firmness for different soak times in calcium chloride and record your results.
• Test different calcium salts that are food safe, such as calcium lactate, and compare gel properties.
• Try side by side concentrations of calcium chloride or alginate to see how concentration affects gel strength.
• Use two colors of alginate in one syringe loaded in layers to create striped worms.
• Explore reversal by soaking finished worms in plain water and observing any softening over time.

• Wear chemical splash goggles and nonlatex gloves. Secure loose hair and clothing.
• Calcium chloride can irritate skin and eyes. Avoid contact and wash hands after the activity.
• Do not eat any materials or products from this demonstration.
• Cover work surfaces to manage spills. Wipe up splashes promptly to prevent slipping.
• Use syringes without needles only. Supervise participants at all times.
• Dispose of small amounts of diluted solutions down the sink with plenty of water if permitted by local rules. Place solid gels in the trash.

• What turns liquid alginate into a solid worm when it touches calcium chloride? (Calcium ions replace sodium and ionically crosslink adjacent alginate chains, forming a gel network.)
• Why does a longer soak in calcium chloride make a firmer worm? (More calcium diffuses in and creates more crosslinks, increasing rigidity.)
• Why can a cut worm be “healed” by dipping the cut end into calcium chloride? (Fresh alginate at the surface crosslinks quickly when calcium contacts it.)
• Is this the same as making new covalent polymer chains? (No. The main chains are already polymers. The firmness comes from ionic crosslinks between chains.)
• How could you test the effect of concentration on gel strength fairly? (Change only one variable at a time, keep temperature and timing constant, and measure bend or break force consistently.)