Month: March 2017

1.  Styrofoam contains pores which traps air within them. Once styrofoam is dissolved in acetone, the trapped air are released and therefore, large amount of styrofoam is able to dissolve in small amounts of acetone. However, the dissolved styrofoam remains in the acetone mixture. Hence, after the removal of acetone, the solid obtained is the solid itself and of higher density.

2a. The more branching it has, the higher cross-linking will lead to a stiffer material which will not be flexible. When the LDPE is stretched, the material narrows and necks down. The molecules align parallel to each other and in the direction of pull. The alteration is non-reversible and the material will break if the pulling continues.  Hence, this is not very ideal for glove lining as LDPE does not have the desired strength.

2b. HDPE on the other hand is much harder and stronger than LDPE. Also, the weak extensive dispersion forces in HDPE allows the molecules to slip past one another and thus allow the material to stretch for a considerable length without breaking.

3. No, the same thing will not happen to paper. The weak but extensive dispersion forces in plastic also allow the molecules to slip pass one another allowing the plastic to stretch and neck. This alteration of the three-dimensional structure is not reversible, and if the pulling continues, the plastic breaks. Whereas for paper, it is made from cellulose. As cellulose is a rigid molecule, they are unable to slide pass each other and hence, the molecule are not free to become align with each other and thus, they are less flexible as compared to plastic.

4a. The four properties are: (1) non-toxic (2) non-immunogenicity (3) low-cost (4) degradability.

4b. For soft contact lenses, Silicon Hydrogel are used. For hard contacts lenses, polymethyl methacrylate (PMMA or Perspex/Plexiglas) are used. The desirable properties of contact lenses are durability, transparency and inert to chemicals on the eye surface. The lenses have to be non-toxic, comfortable and must be able to fit the shape of the eye.

4c.  Hard contact lenses made of PPMA are usually rigid and non-permeable to gases whereas soft contact lenses are hydrophilic and has high oxygen permeability and flexible, making it more comfortable.

1a.  Coal-fired plants release SOx which reacts with water to form sulfuric acid. These many molecules of sulfuric acid forms tiny droplets of aerosols that do not absorb sunlight but instead reflect the sunlight, reducing visibility.

1b. pH of natural rainwater is approximately 5.3. Hence, the pH of the average rainfall in Mammoth Cave National Park should be approximately 4.3.

2. NOx and SOx are main contributors of acid rain.

2a. By hanging your laundry outside to dry, this reduces the electricity consumption as the electronic dryer is not used. Hence, less energy is needed to be generated from power plants, resulting in burning of less fossil fuels such as coal. Less SOx and NOx are produced, reducing acid rain formation.

2b. Less usage of automobiles will reduce consumption of fossil fuels hence reduce emissions of NOx from automobile vehicles.

2c. Same amount of energy is required to run full and small loads. Running dishwaters and washing machines with small loads will not optimise the energy usage. Reduce frequency of running dishwaters and washing machines will reduce the energy needed to be generated from power plants, hence less SOx and NOx will be produces.

2d. Adding additional insulation will reduce the heat loss of hot water to surroundings. Hence, less energy will be needed to maintain the hot temperature of water heaters and pipes, decreasing production of NOx and SOx from power plants.

2e. Consuming local grown goods will reduce the need for transportation of imported goods across further distances. Thus, less emissions (NOx) as there is less usage of transportation vehicles.

3a. Acids:

1. Hydrochloric acid, HCl.
2. Sulfuric acid, H2SO4.
3. Ethanoic acid, CH3COOH.
4. Nitric acid, HNO3.
5. Phosphoric acid, H3PO4.

Bases:

1. Sodium hydroxide, NaOH.
2. Potassium hydroxide, KOH.
3. Barium hydroxide, Ba(OH)2.
4. Lithium hydroxide, LiOH.
5. Calcium hydroxide, Ca(OH)2.

3b. Acids: Sour taste, turns blue litmus paper red, corrosive

Bases: Slippery feel, bitter, turns red litmus paper blue.

4. Acid rain can be caused by a few factors:

1. Pollutants such as SOx and NOx are produced from places such as power stations and oil refineries.
2. Harmful emissions such as NOx from automobiles.
3. Open burning of waste materials

The pollutants mentioned above dissolve in rainbow to produce acid rain.

Apart from the factors mentioned above, slash and burn from neighbouring countries such as Indonesia may contribute to haze and acid rain in Singapore. This is because  pollutants such as NOx and SOx which build up in Indonesia are transported to Singapore under favourable wind conditions.