Category: My Work

1a) C4H9N3

b)

c) Amine, the hybrid aromatic ring containing both carbon and nitrogen atoms.

2a) C16H21N3

b) Both compounds contain aromatic rings and amine functional groups.

3) Physiological response: a, b, d, e

Inhibition of the growth of substances: c, f

4a) Herbal remedy is safe if taken under doctor’s instruction, as the active ingredients in herbs are usually not in large amount. This makes herbal remedy has milder side effects. Not taking herbal remedy and prescription or OTC medicines at the same time can avoid the side effect issue. The herbal supplement is also regulated by government.

b) Herbal medicines are categorized as health supplements, which can be imported and sold without legislation.

1. The foaming agent used during the polymerization process will make the styrofoam much bigger than their original size of the monomers. The bigger size is due to the polystyrene foam containing air. When dissolving styrofoam into acetone, the air inside is released so the solid remained after evaporation of acetone is much denser.
2. (a) The branched LDPE has much weaker intermolecular forces between the branched polymers, which may be easily cut through by sharp tools. (b) Linear HDPE which contains linear polymers will have more surface area of polymer chains to form stronger intermolecular interactions, making the linear HDPE gloves have high resistance to being cut.
3. Paper cannot be stretched and maybe broken. Paper is made of cellulose which is a polymer connected through covalent bonds. When these covalent bonds are broken, they cannot form again by themselves. On the contrary, plastic bags which is made of polymers interacting with each other by weak van der waals’ forces can be stretched because this intermolecular forces can be easily reformed as long as the polymers are close together.
4. (a) Less toxicity to human body, good biocompatibility, lower corrosion rate, easy processing and workability (b) Polymethyl methacrylate (PMMA)- hard, Silicone hydrogels- soft  (c)  Hard contact lenses are not comfortable to wear, but they are more chemically inert, allowing them to be worn in more challenging environment than soft lenses. Soft lenses have high oxygen permeability and are comfortable to wear. The lenses can be hydrophobic and may make eyes dry when wearing it.

1a. The combustion of coal produces SO2 and forms aerosol in the air which leads to poor visibility.

b. Natural rain has pH of 5 to 6. “Ten times more acidic” means that [H+] increases by 10 times. Every 10 times increase in [H+] leads to decrease in 1 pH value. The pH value at the National Park is 4 to 5.

2.
A. Reduce electricity usage and increase water vapour
B. Reduce co2 emission which can become acid when contact with water
C. Reduce electricty usage which usually use coal as power source which emit co2 to the air
D. Improve efficiency of the heater which can reduce the usage of electricity which usually use coal as power source which emit co2 to the air
E. Saving the energy which wasted from transporting non local food.

3a. Acids – HCl (hydrochloric acid), H2SO4 (sulfuric acid), CH3COOH (acetic acid), CHNO3 (Nitric acid), H3PO4 (Phosphric acid)

Bases – NaOH (sodium hydroxide), KOH (potassium hydroxide), NH3 (ammonia), Mg(OH)2 (magnesium hydroxide), Ba(OH)2 (barium hydroxide)

b. Acids turn litmus paper to red while bases turn litmus paper to blue.

4. Issues in Singapore: Acid rain causes the acidification of the stream and disappearance of species. The acid deposition mainly comes from industrial pollution and use of cars, which produces large amount of SO2 and NOx. SO2 from Indonesia due to burning of trees will increase the acid deposition level in Singapore.

 

1. The first method is boiling. Boiling the water will kill off the microorganisms, bacteria and pathogens. In terms of cost, this process is a rather inexpensive. However, boiling requires time and does not remove chemical contamination. It requires fuel and may release soot and carbon dioxide into the atmosphere. The second method is the usage of iodine to purify the water. It is inexpensive and easy to administer. However, it should not be used for the long term, and pregnant ladies and people with thyroid should avoid such purification.
2. This is because it requires a large amount of energy, high cost and causes negative environmental impacts such as releasing concentrated waste stream on the ecosystem.
3. a) Corrosion of lead pipes or solder in drinking fountains or water storage tanks.b) No. During the chemical research, there may be common use of acids or other minerals that corrodes the lead pipes or solder, bring the dissolved lead into the water.
4. Water-soluble vitamins are considered to be be polar compounds as they have mostly polar groups than non-polar groups. On the other hand, fat-soluble vitamins are considered to be non-polar as it can dissolve in fat or lipid, which are non-polar molecules having predominantly non-polar hydrocarbon.

1. The Earth does not cool rapidly because the Carbon Dioxide and Water Vapor on the Earth’s surface absorb the heat from the Sun and radiate the energy to keep the Earth warm.
2. The statement is incorrect. They do not realise that the extreme weather they are experiencing could in fact be a result of climate change brought about by global warming.
3. This is because the absorption of microwave radiation by water vapor in the atmosphere will interferes with the detection of intended objects.
4. In the short run, the burning of fossil fuels contributes to global warming and worsen the air quality. Air quality has a direct impact on our everyday lives and can affect human health over a much shorter time frame than processes such as global warming. It is thus more of a concern in the short run.In the long run, global warming will be the most serious problem, as it may cause people who live at the low altitude islands to have no place to live due to the rise in water level cause by the melting of ice in the north and south pole.

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