Slime Lab

Slime is produced by mixing 4% solution of polyvinyl alcohol with a mixture of boric acid(weak acid) and sodium hydroxide (strong base). They react to form sodium tetraborate (borax) Borax acts as a cross-linker, holding the long stringy polyvinyl alcohol molecules together making a slimy semisolid gel-like substance that can be picked up, stretched, broken, molded and bounced even though it is 96% water. Cross-linking gives the network stability, but when subjected to a shearing stress it can be broken down. This polymer is quite soluble in a large excess of water and it tends to turn fluid under stress.

Polyvinyl alcohol contains a long chain of carbon atoms with hydroxyl groups on every other carbon atom. It is a linear polymer and can have a molar mass of up to 150,000g/mol with almost 7000 carbon atoms in a row. Polyvinyl alcohol is made by connecting hundreds of polyvinyl alcohol molecules. Most large substances are not soluble in water, but the large numbers of hydroxyl groups that can form hydrogen bonds with water contribute strongly to the remarkable solubility of polyvinyl alcohol. Hydrogen bonds are not true chemical bonds. They are one of the forces of attraction that hold one molecule close to another. Hydrogen bonds are broken as the temperatures of a system rises causing molecular motion to increase.

Materials

Goggles, cups, 10ml graduated cylinder, pH paper, stirring rod, 4% polyvinyl alcohol solution, .2M boric acid solution, .2M sodium hydroxide solution

Procedure

Part A

1.Place 2ml of boric acid in a paper cup and measure the pH by touching a wet stirring rod on the paper

2.add 1 ml of NaOH and test the pH again

3.place another 1ml of NaOH in and test the pH again

4.add another 1ml of NaOH in and test the pH again

5.you should now have a 2ml boric acid and 3ml NaOH solution-SET THIS ASIDE FOR LATER

Part B

1.In a new cup, place 10ml of polyvinyl alcohol solution and add 2ml of boric acid-stir and observe the viscosity

2.add 1ml of sodium hydroxide, stir and observe the viscosity

3.add another 1 ml of sodium hydroxide solution and stir

4.add another 1ml of sodium hydroxide solution and stir

Part C

1.pour 10 ml of polyvinyl alcohol in a new cup and add the mixture from part A

2.stir and observe the nature of the mixture

4.place this slime in a beaker and slowly heat in a beaker

Part D-properties of slime-RECORD ALL OBSERVATIONS AS YOU PROCEED

1.After cooling to room temperature, remove it from the beaker and roll it into a ball and place it on a flat surface. What happens to it over a period of time?

2.Hit the relaxed ball of slime-what happens

3.pick it up and stretch it slowly

4.roll it into a cylinder and pull it rapidly

5.try to bounce it

6.Try to dissolve a small piece of slime in water

7. in a new cup, place 2ml boric acid solution and 3ml of sodium hydroxide solution with about 1 gram of salt

8.stir this new mixture completely

9.add 10ml polyvinyl alcohol solution-compare it to your other slime ball

Data

Part A

pH of boric acid

pH boric acid + 1 ml NaOH

pH boric acid + 2 ml NaOH

pH boric acid + 3 ml NaOH

Part B

What did you observe as you added NaOH slowly to the boric acid and polyvinyl alcohol solution?

Part C

What did you observe as you added the NaOH immediately to the boric acid and polyvinvyl alcohol solution?

Was there any difference between Part B and Part C on using a premixed set of boric acid and sodium hydroxide solution?

What happened to the slime as you heated it?

Part D

What did you observe when you did the following:

1.let the slime sit on a surface

2.hit the ball with your hand

3.stretch it slowly

4.stretched quickly

5.tried bouncing it

6.mixed a small piece with water

7.make a salt mixture

Analysis

1.Why did it appear to be soluble in water?

2.Why does it appear to break down in heat?

3.What may have happed with the addition of salt?

4.What property allowed you to stretch and perhaps bounce the slime?