Activity 3.7 - Properties of polymers – dissolution of polymers

• Understanding of structure of polymers and explanation of dissolving of polymers. Understanding of factors which influence solubility of polymers.

• Chocolate,
• sugar,
• oil,
• water,
• 4 beakers (50-100 mL),
• bar,
• tooth

Task:

Explore, whether the polymers are soluble in some solvents and what is responsible for the solubility.

Procedure:

1. Chew the chewing gum up and divide it to three parts, two smaller and one bigger. Try to save the bigger part in good condition, you will chew it again.
2. Prepare 4 beakers. Pour the oil into two beakers, then pour water also into two beakers. Try to dissolve the chewing gum in one beaker with water and, consequently, in beaker with oil. Do the same with sugar. Write down the results. In the other beakers with water and oil, try to dissolve the chocolate. Taste the water. Write down the results.
3. Take the biggest part of chewing gum and try to chew it up. Chew the chewing gum and add a chocolate. Chew it together. What happened? Write down the results.

Discussion:

Polymers usually are not very well soluble and their dissolution takes longer, because whole macromolecular chain has to be surrounded by molecules of solvent. However, it does not mean that polymers are insoluble. Some of them is possible to solve. On the other hand, we can deduce that cross-linked polymers are insoluble, because, in fact, they are “only one” molecule. Polymer in a chewing gum is polyisoprene, hence, it is formed of linear nonpolar chains. Regarding solubility, in case of polymers, the same rules as in the case of other substances are applied. Thus, nonpolar linear polymers are soluble in nonpolar solvents and polymers with polar chains and/or groups are soluble in polar solvents. Polyisoprene is nonpolar substance, hence, it is soluble in nonpolar solvents like oil, petrol etc. In the case of our experiment, the chewing gum is soluble in oil, but, it is not soluble in water. On the other hand, sugar, having a polar groups, is soluble in water but insoluble in oil. Chocolate contains cacao milk, which is a type of nonpolar oil. Hence, when we chew the chewing gum together with chocolate, the chewing gum is dissolved in cocoa milk.

What is the chewing gum? Is it polymer? What polymer?

Polymer in a chewing gum is polyisoprene, hence, it is formed of linear nonpolar chains. It is a polymer similar to a rubber.

Why the chewing gum was dissolved in a chocolate? Will be all the polymers solved in chocolate?

Polyisoprene is nonpolar substance, hence, it is soluble in nonpolar solvents like oil, petrol etc. In the case of our experiment, the chewing gum is soluble in oil, but, it is not soluble in water. On the other hand, sugar, having a polar groups, is soluble in water but insoluble in oil. Chocolate contains cacao milk, which is a type of nonpolar oil. Hence, when we chew the chewing gum together with chocolate, the chewing gum is dissolved in cocoa milk.