Science Concept: This is a demonstration on polymers. The chemical sodium alginate becomes cross-linked with calcium ions.
* 2 grams of alginic acid sodium salt
* 1 gram of calcium chloride dissolved in 100 mL water (For multiple shows, you could make a stock solution of 5 g calcium chloride and dissolve in 500 ml water. Then use 100 mL of this each time.)
* a large syringe
* 100 mL glass graduated cylinder
* food coloring
* Two 250 mL beakers
1. In one beaker, add 100 mL of water.
2. Slowly and gradually sprinkle the 2 g alginic acid in the 100 mL of water while stirring vigorously ( you do not want to pour too much of the alginic acid into the water at one time because it becomes clumped).
3. Put 3-4 drops of food coloring into the alginic acid solution.
4. Add 100 mL of water into the other beaker and then add one gram of calcium chloride with stirring.
5. Pour the calcium chloride solution into the 100 mL graduated cylinder.
6. Fill the syringe up with the alginic acid solution. Put the tip of the syringe into calcium chloride solution in the cylinder and at a "medium" speed squirt the solution into the graduated cylinder (make sure the tip of the syringe is already inserted into the calcium chloride solution before squirting).
7. A gel will form when the two solutions are mixed together, forming the snakes. Pull the colored snakes out of the graduated cylinder for the students to see.
Introduction: Who likes snakes? Do you think it is possible for me to create a snake right here in your classroom?
Explanation: The sodium alginate is a carbohydrate that can be found in seaweed. This is a natural polymer containing glucose monomer units. There are many of the glucose monomer units used to create the polymer which is already formed when dissolved in the water solution.
One part of the glucose has been changed into the sodium salt of an acid. When the sodium alginate is squirted into the calcium chloride, an exchange reaction takes place. The calcium ions replace the sodium ions. Because the calcium ions have a +2 charge, several polymer chains may be cross linked to form a thicker polymer. The sodium alginate is also a thickener often used in the production of certain foods such as the red stuffing in green olives, ice cream and fruit-filled snacks. This sodium alginate cross-links with the calcium ions to form the snake-like structure of the goo that was created. The "snake" is actually a cross-linked polymer.
Safety: Handle the chemicals carefully.
Waste Disposal: The snake goo may be thrown away and the water may be put down the drain.
Source: .Waldman, Amy Sue; Schechinger, Linda; Govindarajoo, Geeta; Nowick, James S.; Pignolet, Louis H. The Alginate Demonstration: Polymers, Food Science, and Ion Exchange J. Chem. Educ. 1998 75 1430. (November1998)