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Lab: Making a Polymer Bouncing Ball
Principle Investigated: Make a polymer ball and observe the changes in physical properties. Which polymer ball will bounce more?
Hypothesis:
Student Prior knowledge:
Physical changes = alters the form or appearance, but the material is the same.
Chemical changes = change that makes a new substance
Explanation:
- Balls have been toys practically forever, but the bouncing ball is a more recent innovation.
- Bouncing balls were originally made of natural rubber, though now bouncing balls can be made of plastics and other polymers.
- You can use chemistry to make your own bouncing ball.
- The bouncing ball in this activity is made from a polymer. Polymers are molecules made up of repeating chemical units. Glue contains the polymer polyvinyl acetate, which cross-links to itself when reacted with borax. (see diagram below)
- This is an experiment using different amount of borax, glue, and cornstarch. The more cornstarch you add, the ball will expand. The more glue you add, the slimier the ball gets. The more borax you add, the less sticky the ball gets.
Materials:
1) borax
2) white glue
3) corn starch
4) water
5) beaker
6) spoon
7) graduated cylinder
8) meter stick
Procedure:
A) Ball #1:
1) In a glass beaker, mix 3 level spoonfuls of glue and 5 mL water.
Then add 1 level spoonful of borax.
2) DO NOT STIR. Allow the ingredients to interact on their own for
10-15 seconds and then stir them together to fully mix. Once the
mixture becomes impossible to stir, take it out of the beaker and
start molding the ball with your hands.
3) The ball will start out sticky and messy, but will solidify as you
knead it.
4) Record observations about the ball.
Observations such as composition of the ball, diameter of the ball, and how sticky
it is and the time it requires to solidify into a ball.
5) Use the meter stick and hold the ball at a height of 50 cm above
your desk. Drop the ball and record how high it bounces.
B) Ball #2:
1) Mix 3 level spoonfuls of glue, 5 mL water, and 1 level spoonful of
cornstarch. Then add 1 level spoonful of borax.
2-5) same as ball #1
C) Ball #3:
1) Mix 3 level spoonfuls of glue and 1 level spoonful of cornstarch.
Then add 1 level spoonful of borax.
2-5) same as ball #1
D) Ball #4:
1) Mix 3 level spoonfuls of glue, _______ mL water, and _________
level spoonfuls cornstarch. Then add ______ level spoonfuls of
borax.
Data:
Post lab Questions:
1) Does making Polymer ball involve chemical reaction or physical reaction, explain your reasoning?
2) Give an example of a chemical change and physical change.
3) As candle burns, chemical changes take place. Describe tow of this changes, and explain how you know that these changers are chemical changes and not physical changes.
Answers:
1) It involves chemical reaction because a new substance is formed. The ingredients in this reaction as borax, starch, and glue react with each other to form a solid substance.
2) An example of chemical reaction would be baking soda and vinegar producing gas, carbon dioxide, indicating a chemical reaction. An example of physical change would a melting of solid ice cube into water. This is a physical change because melting does not change the identity of a substance and it can be undone.
3) Wax burning is a chemical change because heat is liberated. The wick burning is another chemical change. The wick changes into new substances that have different properties.
Conclusion:
Compare your results with other groups and draw a bar graph for ball # 1-4. Do you accept or reject your hypothesis, why?
Application to Everyday Life:
· Natural rubber is made of polymer which is taken from bark of the tree. Rubber is an elastomer used in everyday life from gloves, balloons, to tubes and tires.
· Plastics are made of polyethelene. Plastics are used in everyday life like bottles, bottle caps, and plastic container for storing food.
· Fibers are also polymers as cotton, wool, silk, polyester, rayon, and nylon and we used them for clothing.
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