GAK

What is Gak? Is Gak a solid or liquid? How is it like a solid? How is it like a liquid? Can you pour Gak? What happens to Gak when you set it on a table for a minute? What kinds of shapes can you make with Gak? Does Gak break? How far can you stretch Gak? What happens when you stretch Gak and let it go? Can you get bubbles inside Gak? Can you get bubbles out of Gak?

What is Gak?

You made Gak by mixing together glue and borax. Most brands of white glue contain millions of long strands of molecules that are linked together like a chain. (See diagram below.) These chains are able to slip and slide freely over one another like strands of freshly cooked spaghetti. Although they can slip around, the chains are so long that they interfere with each other, causing the glue to be rather thick. When you add the borax to the glue, two things happen. First, the borax links the long strands of glue together - just as rungs link the two sides of a ladder. This is called cross-linking. (See diagram below.) This process creates a net-like structure, making Gak behave like a solid. In turn, the net-like structure traps the water in between the strands. This trapped water is what makes Gak behave like a liquid. Thus, Gak acts like both a solid and a liquid.

·¾·¾·¾·¾·¾ + Borax ® ·¾·¾·¾·¾·¾

·¾·¾·¾·¾·¾

Strand of glue molecules

Strands of glue molecules

cross-linked by borax

There are two simple things you can do to keep your Gak lasting a long time:

· Wash your hands before playing with Gak;

· Keep the sealed, labeled plastic bag in the refrigerator when you’re not playing with it.

How to make Gak at home:

We strongly recommend that you do this activity with a parent.

Materials:

1 tablespoon 20 Mule TeamÔ Borax 2 disposable mixing cups

2 tablespoons white glue (Elmers) stirrer

water small plastic bag for storage

food coloring (optional)

What to Do:

1. Make sodium borate by adding 1 tablespoon of 20 Mule Teamä Borax powder to 1 cup warm water. Stir until all of the powder has dissolved.

2. In a separate container, mix 2 tablespoons glue and 2 tablespoons water. Stir well. (Optional: Add 3 drops of food coloring to the glue/water mixture and stir.)

3. Add 1 tablespoon of the sodium borate to the glue/water mixture.

4. Stir and let sit in the cup for a few minutes.

5. Take it out and play with it!

6. Remember to always store in a clearly marked, sealed bag in the refrigerator.

More Stuff You Can Do:

· What happens if you change the amount of sodium borate? What happens to the Gak?

· What if you change the amount of glue? What happens to the properties of the Gak?

· What if you use more or less water? What happens to the properties of the Gak?

· Use coins or small objects to make imprints in the Gak. Do these imprints last?

· What happens to Gak in the refrigerator? What happens if you freeze it?

Warning:

· Do not leave Gak on fabric, vinyl, or wood; it may damage them.

· Do not eat Gak!

· Make sure your plastic bag is labeled especially when it’s in the refrigerator. Scientists always label their stuff so that everyone knows what it is.

· Do not pour Gak down the drain or in the toilet. When you are finished with it, throw the sealed plastic bag in the garbage.

· Never taste anything used in a science experiment.

· Follow all safety precautions listed on the labels of the glue and the borax.

· Wash your hands after playing with the Gak.

References:

Sarquis, A.M., Kibbey, B., Smyth, E. 1989. Science Activities for Elementary Classrooms. Batavia, IL:Flinn Scientific.