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The World of Polymers and Plastics

Question 1

Acetone is a weak acid that most polymers are able to dissolve in. Styrofoam packaging is held in a rigid shape due to its bonds between the section of the chains, holding the polymer in its rigid shape. This rigid shape does not efficiently pack the long-chain polymer, thus having many air-pockets. When the styrofoam is dissolved in acetone, the bonds holding the long-chain polymer in its rigid structure is broken, while the covalent bonds holding atoms in the long-chain polymer is still intact. The rigid stucture of the polymer collapse, condensing into an efficiently packed solid, eliminating the air pockets. Hence, the final solid styrofoam is much denser than before.

Question 2

a) LDPE cannot be used because it does not have the strength needed.

b) Molecules of HDPE must line up so that they provide the strength required. HDPE is flexible enough to be successful in this application.

Question 3

No. When a piece of plastic is stretched, the weak but extensive forces allows the molecules to slip pass one another allowing the plastic to stretch and ‘neck’.The molecule will rearranged itself parallel to the direction of force applied. This is plastic deformation. The deformation caused by the force on the plastic is irreversible. Further deformation will cause the structure to fracture. Paper is made of cellulose.  It has crystalline regions  as it is made up of a linear chain of glucose monomers. Therefore, the structure is more compact and it is not as flexible as a plastic bag. It does not have the characteristic of being able to deform plastically. Thus, it will fracture when the same puling force is applied to it.

Question 4

(a) Non-toxic, Insoluble in bodily fluids, Not too rigid, Non-reactive in the body

(b) Hard lenses: Polymethyl methacrylate (PMMA)

Soft lenses: Silicon polymers e.g. Polymacon (38% water)

Properties: non-toxic, allows oxygen to pass through to reach eyes, not too thick to provide comfort, shape of lenses needs to be similar enough to fit the eye contour

(c) Hard contact lenses are usually made of PMMA, a non-gas permeable and rigid plastic.

Soft contact lenses are usually made of silicon, which has breathable properties to allow oxygen to pass through and reach the eyes. Soft lenses generally makes the eyes more at ease as it is more flexible than the hard lenses.

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Neutralising the threat of acid rain

1a) Coal-fired plants produces varying amounts of SO2 which reacts with oxygen molecules to form SO3, which acts in the formation of aerosols. Aerosols do not absorb sunlight and reflects it instead, thus leading to poor visibility.

1b) The natural pH of rainfall is between 5 to 6. Hence, if the average rainfall in Mammoth Cave National Park is 10 times more acidic than natural, then the pH of the rainfall in the park should be between 4 to 5.

2a,c) Reducing the electricity usage will decrease the power generated by power plants, thus decreasing the emissions of NOx and SOx.

b) Using public transportation and decreasing the use of transportation will decrease the number of automobiles being used, thus decreasing the emissions of NOx produced from the combustion of petrol in the combustion system in the automobile.

d) insulating hot water pipes will reduce heat loss and raise water temperature by 2-4 fahrenheit, thus the water temperature setting can be lowered, decreasing the electricity usage.

e) purchasing locally produced food will reduce the need to import food and agricultural products, thus decreasing the emissions of aerosol by-products from the automobiles required for transportation.

3a) Acids: HCl, H2SO4, H3PO4, HNO3, H2CO3

Base: NaOH, Ba(OH)2, Mg(OH)2, NH3, KOH

3b) Observable properties generally associated with base are: changes of litmus colour from red to blue, slippery, and bitter taste

Observable properties generally associated with acids are: change of litmus colour from blue to red, sour taste, PH meter shows a reading of less than 7

4) 

Acid deposition originates inside Singapore as Singapore being an urban jungle, with its population being one of the most densely populated country in the world, results in a lot of human activities being carried out (e.g, transportation) which leads to high levels of atmospheric NO2 being produced. With the trace amounts of VOC that is present in the atmosphere, acid rain is produced.

Acid deposition also originates outside Singapore due to the activities conducted by nearby countries. For example, acid deposition originates from Indonesia due to forest fires which leads to haze.