Both polystyrene and cornstarch are made of polymers, which are long-chain molecules that have a basic repeating unit. Some polymers are polar (such as cornstarch), while others are nonpolar (such as polystyrene). The polar parts of cornstarch are hydroxy (–OH) groups that hang off the main chain. These hydroxy groups interact with water molecules to form hydrogen bonds, and as a result, cornstarch is soluble in water. Polystyrene has no hydroxy groups and is nonpolar, so it does not dissolve in water. The crosslinking structure of polystyrene can be broken down in certain organic solvents such as acetone. However, such solvents are usually toxic and harmful to the environment. This Activity compares polystyrene and cornstarch packing materials ("peanuts"). Both are made of polymers, but because of their composition they behave very differently in various solvents. Students extrapolate how these differences in behavior relate to environmental effects.
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