Friday, December 7, 2012

Hoax Demo/Glue and Borax Polymer Lab

Today Ms. Leland played a joke on us. She showed us a video that convinced us that it was possible to change the polarity of water and turn it into little marbles. The video had many steps that supposedly turned water into solid balls. First, make sodium acetate by mixing baking soda and vinegar. Then, put that mixture in the freezer for ten minutes. Take it out of the freezer and add the mixture to calcium bicarbonate. Then, add ½ cup of iodized salt. Boil for seven minutes, and then, let it sit for fifteen minutes. If you followed these instructions you would supposedly end up with solid water marbles. However, this is not what happens. If you follow these instructions you will end up with a mess in your kitchen and no solid water marbles.

Ms. Leland used Super Absorbent Polymers to make “solid water.” They are a plastic that starts out tiny, but when they are exposed to water they expand and turn into balls. The balls feel very rubbery, but they are a solid, so it is not very easy to break apart. They also have a little bounce in them. The reason they look clear in the water, and you cannot notice them is because they refract light the same way that water does, so they look the same.


The polymers are tiny to begin with but...

… if they come in contact with water, the polymers turn into balls.

After the demonstration performed by Ms. Leland, we created our own polymers.

Hypothesis: Borax and Elmer’s glue solution mixed together will create a putty mixture because the chemical reaction will result in Borax coming in between the Elmer’s glue structure and bonding it together. Borax will be the cross-linking agent.

Procedures: Add one heaping teaspoon of Borax to 100 mL of water. Stir the solution together. In a separate beaker add 5 mL of water to 25 mL of Elmer’s glue. Add 40 mL of the Borax solution to the Elmer’s glue solution. Stir rapidly as the new solution changes in texture and form. Empty the extra Borax solution in the sink.

Data and Analysis:


 
This is the glue solution before the Borax was added. It was very runny and obviously a liquid.

This is the Elmer’s glue solution while being vigorously stirred. Because I was stirring so hard bubbles began to form. It was beginning to become a solid, but it was not there yet. 

This is a diagram of the Elmer’s glue being stirred with the Borax solution.

This is the Elmer’s glue after it was stirred. It was a solid. It was still wet, so the blob was very slimy. The mixture felt very gelatinous. 

When the slime is stretched slowly, it does not rip. It stretches very far, though. When the slime is stretched rapidly it rips like a piece of paper would. 

The slime could easily be molded into any shape when it was wet. When it was dry it could still be molded, but it was not as easy.

Questions:
1. How is slime visco-elastic?
Slime is visco-elastic because it does not rip easily when it is stretched.

2. What are the physical properties that change as a result of the addition of sodium borate to the Elmer’s glue?
The sodium borate transformed a liquid glue solution to somewhat of a solid.

3. What would be the effect of adding more sodium borate to your cup (your thoughts only)?
Adding more sodium borate would make the slime less like jelly and more like a hard substance. This is because the glue is the liquid part of the slime and the borax is the solid part. If there is a higher amount of solid, then the slime will feel more like a solid.

4. After making observations on the dried glue, how does water affect the elasticity of a polymer? What is elasticity?
Elasticity is the amount an object can be stretched without breaking. Water increases the elasticity because it makes it easier to stretch and harder to break.

5. Find and circle the repeating unit in the polymer below.

6. What is the structural formula of the poly(vinyl alcohol) monomer circled above?

7. In the picture below, circle the borax cross-linking agent.
Conclusion: I had such a great time conducting this experiment. It was fun to play with the slime afterward! :) My hypothesis was accepted because the Borax was essential in keeping the slime a solid. It bound the molecules of the glue together, so that it became a solid. I learned that cross-linking agents keep polymers bound together as solids. I would have never expected Borax to turn a liquid glue into a solid! Water also has effects on polymers. Water makes the polymers have more elasticity. If I were to try this experiment again, I would use a different cross-linking agent. It would be interesting to compare the results if there are different cross-linking agents. In conclusion, this lab was extremely enjoyable and educational because I learned about cross-linking agents in polymers and had fun in the process!

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