Glurch and Oobleck
Objective
The objective of this lab is to investigate the properties of a pair of colloids that you will make yourself. A secondary objective is to enjoy doing some science. The Oobleck is named for a 1949 Dr. Suess story called Bartholemew and the Oobleck.
Materials
50 mL beaker
15 mL white glue
5 - 20 mL water
10 mL 4% borax solution
zip-top baggie
food color
50 mL beaker
30 mL of cornstarch
15 mL water
food color
various objects for performing tests (you decide!)
Background
Some materials do not conform neatly to the designations for solids, liquids, and gases. For example, a colloid is a material that consists of one substance suspended within another. The suspended material is comprised of particles so small that they don’t sink to the bottom of the second substance. Together, the two materials display properties unlike those of their separate components. Some examples: smoke (a solid suspended in a gas), fog (a liquid suspended in a gas), meringue (a gas suspended in a liquid), protoplasm, homogenized milk, synthetic rubber, and mayonnaise. The Oobleck is an example of a colloid of starch and water. Starch molecules are long chains of simple sugar molecules. Long chains of molecules formed from repeated units are called polymers. The repeating units are called monomers. Starch is naturally occurring polymer made by many organisms on Earth and it is used as cellular food storage since the sugar monomers it is made of can be broken off the long chain and used for energy. In water the long starch chains assume a globular shape. The globular starch molecules can become entangled when the they are suspended in water. This entanglement leads to the odd properties of the Oobleck.
The Glurch is an artificial polymer. White glue is a polymer of a chemical called vinyl alcohol. The long chains of polyvinyl alcohol can flow around and over each other. When you add borax solution to the polymer it causes what is called cross-linking. This makes it harder for the long chains to flow past each other. The stickiness which slows their movement is caused by hydrogen bonds: chemical bonds that have a certain strength but which are easily broken and reformed elsewhere.
You will be investigating the properties of these two strange substances. The properties you should investigate are viscidity (stickiness), resiliency (elasticity), and fluidity (ability to flow). You will be asked to come up with your own tests for these properties. Some suggestions will be given.
Safety
Don’t eat any of the materials.
Procedure
- As always, remember to write carefully in your lab notebook what you do in the lab.
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Glurch
- Measure 15 mL of the glue into the cup, add the water; mix thoroughly. (Vary the amount of water to achieve different outcomes: more water makes a gloppier gel and less water makes a bouncier gel).
- Add one or two drops of food coloring, if desired
- Add the borax solution to the cup; stir the mixture to make the slime; take it out of the beaker and knead with your hands to complete the mixing
- As soon as you have finished getting the Glurch out of the beaker please clean the beaker immediately: otherwise it will be much harder to clean later.
- Glurch can be kept in a refrigerator when you are not using it and kept for a long time
- Try the following:
- Devise a way to gauge the viscidity (stickiness) of the Glurch. Is it sticky enough to pick up a piece of paper? A pencil? Try to keep the surface area that touches an object the same for each test.
- Does the Glurch bounce? Can you pull it apart? Try to devise a few tests to discover the elasticity of the Glurch.
- How can you test for fluidity in the Glurch? Try placing it on something with a small hole in it. See whether it will run between your fingers. Hang it from something.
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Oobleck:
- Add 30 mL of cornstarch into a 50-mL beaker
- Measure out about 15 mL of water; add one or two drops of food coloring if desired and add the water a little bit at a time while stirring with a metal spatula.
- When the mixture becomes too thick to stir, remove from the cup and knead in your hands. It can be poured out on the counter-top. Be sure to clean up thoroughly when you are done!
- Add a few drops of water if the Oobleck becomes crumbly
- Try the same tests on the Oobleck that you tried on the Glurch. How do they compare? Which one is stickier? Which one is more elastic (bouncier)? Which one is more fluid (runnier)? As always, write down what you do and your observations in your lab notebook.
Questions
Write some well-thought-out answers to the following questions. Use complete sentences! Some questions will require more than one sentence. Please write as legibly as possible! Use a separate piece of paper for your answers and remember to rephrase the question as part of your answer.
- Describe the way that Glurch looks and its behavior. What makes it weird?
- Describe the way that Oobleck looks and its behavior. What makes it weird?
- What test(s) did you use to find out which substance was stickier? What were the results?
- What test(s) did you devise to discover whether the Glurch or the Oobleck was more elastic? What were the results?
- What test(s) did you come up with to measure the fluidity of the two substances? What were the results?
- What is the definition of a colloid and how does the Oobleck fit that definition? What type of colloid is it? How does Glurch fit that definition? What type of colloid is it? Do some research (not just in a dictionary!).
- What is the definition of a polymer and how does the Glurch fit that definition? How does Oobleck fit that definition? Do some research (not just in a dictionary!).
Colloids at the University of Bristol in England: http://www.chm.bris.ac.uk/webprojects2002/pdavies/contents.html
Polymers at National Geographic: http://www.nationalgeographic.com/education/plastics/index.html
Macrogalleria of Polymers: http://www.pslc.ws/mactest/maindir.htm
See some background information I created about Sodium Polyacrylate (used in the disappearing water trick) and about Poly-vinyl alcohol, the main ingredient in white glue.
Answer these questions to receive credit for your work!