This happens because the gas of the foaming agent has been removed, allowing the styrofoam to become solid and much denser.

a. Branched LDPE cannot be used in this application because it does not have the required strength.

b. The arrangement of the molecules of HDPE provides the required strength and a thin liner of HDPE allows sufficient flexibility.

The same thing does not happen when a piece of paper is being pulled because the molecules in paper are held more rigidly and are not free to become aligned whereas the molecules in plastic can be aligned parallel to each other and in the direction of the pull – allowing the plastic to be stretched.

a.
1. Non-toxic – to eliminate foreign body response
2. Easily sterilised
3. Excellent chemical resistance
4. Acceptable shelf life

b. Polymethyl methacrylate (PMMA) – non-toxic, permeable to oxygen, inexpensive
Silicon Hydrogel – extremely high oxygen permeability, high level of comfort

c. hard contact lenses are more durable as they are more chemically inert whereas soft contact lenses are more flexible and more comfortable.

The rigidity of PMMA allows hard lenses to retain the shape – offering clearer vision therefore providing better comfort.

Desalination of water requires a lot of energy to break strong chemical bonds between salt and water and desalination techniques are relatively more costly. Therefore, it is not used widely.

Water-soluble vitamins are polar compounds because “like dissolves like”. Polar compounds will dissolve in polar compounds,vice versa.

Fat soluble vitamins are non-polar compounds because fat is not polar.

a. do not have to use a dryer machine, so it cuts down electricity and burn less fuels, thus reducing the amount of sulfur dioxide emissions.

b. less automobile transportation, reducing the amount of gasoline used, cutting down nitrogen oxide emissions.

c. do not have to use dishwashers and washing machines that often, so it cuts down electricity and burn less fuels, thus reducing the amount of sulfur dioxide emissions

d. hot water heater and pipes maintain its high temperature for longer periods, reduce the amount of electricity required to heat up the heater and pipes. This cuts down electricity and burn less fuels, thus reducing the amount of sulfur dioxide emissions.

e. less automobile transportation, reducing the amount of gasoline used, cutting down nitrogen oxide emissions.

the reduction of sulfur and nitrogen oxides emissions would lower the occurrences of acid rain

a. coal-fired plants release sulfur dioxide which reacts with water to form sulfuric acid. Many molecules of sulfuric acid form tiny droplets. These droplets form aerosols that do not absorb sunlight but instead it reflects sunlight and reduce visibility.

b. average pH of rainfall is 5.6, so the estimated pH of rainfall in Mammoth Cave National Park is 4.6

a. Exothermic – heat is released from the burning of the charcoal briquette.

b. Endothermic – energy is absorbed by water molecules to form water vapour.

c. Endothermic – energy is absorbed by ice to break the bonds between water molecules to change its state from solid to liquid.

For exothermic reactions, the energy for bond forming must be greater than the energy for bond breaking. Therefore the reactants have a smaller bond strength so it absorbs less heat and the products have a larger bond strength so it produces more heat.

Heat is a type of energy and heat travels from warmer to colder regions. Temperature is a measure of heat energy. Like a cup of hot coffee which transfers heat to its cooler surroundings resulting in a drop of temperature.

a. Octane rating of 98 means a knocking characteristic of 98% isooctane and 2% heptane.

b. The octane rating does not tell us whether the fuel contain oxygenates.