1) Styrofoam contains a lot of air pockets. When dissolved in acetone, the air pockets are released and only the resin is left. That is why it is “solid and much denser”, because the air pockets, which makes it less dense, are no longer there.

2a) LDPE is not strong enough and can be easily broken or cut

2b) Weak but extensive dispersion forces allow the molecules to slip past one another, allowing flexibility. The linear arrangement also allows for greater strength.

 

A plastic molecule.

3) Plastic molecules are aligned in the same direction when stretched. When the pulling continues, it is stretched beyond its ultimate tensile strength and the structure eventually breaks. Paper, however, is brittle. The rigid cellulose molecules in paper are not able move around and change direction when stretched, hence they get torn and not stretched.

4a) Inert, durable, flexible, non-toxic

4b) Hard contact lenses are made of PMMA or poly(methacrylate). Soft contact lenses are made of HEMA, poly(hydroxyethyl methacrylate). Contact lenses need to have high oxygen permeability, refractive properties and hydrophilic. (Reference)

4c) Hard contact lens are easier to wear and clearer, but it is more uncomfortable. It is usually prescribed to astigmatism cases and to correct bi-focal problems. Soft contact lenses are more comfortable and stays in place better. Oxygen is allowed to pass through the contact lens to the cornea due to the flexibility of the soft contact lens when combined with water. (Reference)