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Week 10 Application Exercise

1) Acetone dissolves the polymer causing some of the gas of the foaming agent to escape. As a result, the polymer collapses on itself and becomes denser due to the removal of the gas.

2a) LDPE cannot be used as it does not meet the minimum strength required.

2b) The molecules of HDPE must be arranged in a particular way in order for it to produce the required strength. By using a thin liner of HDPE, it will allow sufficient flexibility for its application in surgical gloves.

3) When a piece of plastic bag is stretches, the plastic becomes thinner and narrower at the center. The molecules align parallel to each other, in the direction of the pull. This action is irreversible as it alters the three-dimensional structure of the molecule and further stretching will tear the plastic. On the other hand, when paper is stretched with the same amount of pulling force, it will tear instead. This is due to the cellulose molecules in paper being more rigidly held in place, thus the molecules are not free to become aligned and will break apart.

 

 

4a) The properties of polymer that would be desirable for use in the human body are (1) stability over time of intended use and (2) non-toxic. (3) wide range of physical and chemical properties to meet the needs of its function by varying the monomer units (4)  Responsiveness to physical stimuli like mechanical stress

4b) There are many types of contact lenses on the market and each consist of a different polymer. One of the earliest polymers used for rigid gas permeable lenses, Polymethyl methacrylate (PMMA), is structurally similar to Lucite and Plexiglas. Silicone-acrylate materials are now more commonly used under trade names such as Kolfocon. Newer rigid gas permeable (RGP) polymers contain fluorine-silicone-acrylate polymers and fluoro-silicones. Polymacon (38% water) is typical of the polymers used for soft lenses and is a polymer of 2-hydroxyethyl methacrylate (HEMA). Other methacrylates include hioxifilcon (48% water) and methafilcon (55% water) or even lidofilcon (70% water). It’s important to find out more before buying a product and manufacturers’ websites are often good sources of information. Some properties that are desirable in contact lenses include being non-toxic, permeable to oxygen, comfortable to wear and inexpensive. The ability to conform to the shape of the eye and ease of cleaning or whether it’s disposable are also qualities that are desirable and need to be considered when manufacturing contact lenses.

 

4c) As mentioned above, PMMA and rigid non-gas permeable plastic are typically used to make hard contact lenses. Soft contact lenses, which were developed to replace hard contact lenses, are made of silicone, which is flexible and allows oxygen to reach the eye. Due to these properties, soft contact lenses tend to be more comfortable.

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Week 7 Application Exercise

1)  Water purifying capsules. The capsules are able to deactivate bacteria, viruses and parasites to make the water safe to drink but it cannot remove impurities in the water.

Boiling of water. Boiling water can remove most bacteria and viruses but it cannot remove impurities in the water. It is the cheapest method out of the three but it is time consuming.

Life Straw. The straw is able to filter most impurities, parasites and bacteria but it does not remove viruses and salt. It is more expensive than water purifying capsules but it is able to purify a larger volume of water.

All these methods are only a small part of the method to purify municipal water supplies. Sedimentation, Filtration, Disinfection, Water Fluoridation, Coagulation and Flocculation are the steps required to purify municipal water supplies.

 

2) This is because a lot of energy is required for the machines to perform desalination. Thus it is very expensive and not sustainable for the environment.

 

3a) The likely major source of the lead in the drinking water could be from the lead water pipe as it may corrode over time which will cause the water to be contaminated with lead.

3b) Yes. This is because some of the chemicals may not be properly disposed of and thus the chemicals may cause the lead water pipe to corrode thus contaminating the water supply.

 

4) Fat is non polar and water is polar. Polar compounds dissolve in polar solvents and non polar compounds dissolve in non polar solvents, hence only the water-soluble vitamins would be expected to be polar molecules.

 

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Week 6 Application Exercise

  1. Due to human activities, a lot of energy is produced at the Earth’s surface constituting, with the reflected energy from the sun, the radiated energy of the Earth. Part of this energy gets trapped in the atmosphere by the greenhouse effect gases. This molecules, enriched in energy, are spinning faster which implies a raise of temperature.

2. Due to global warming, climate change is more extreme such that hot days get hotter and cold days get colder. Colder winter is a sign of fluctuating temperatures due to global warming increasing the need for concern. Therefore the statement is incorrect.

3. Microwave radiation has lower frequency than infrared radiation. Since energy of photons, E = hf (h being the planck constant and f the vibrating frequency), the energy of microwave radiation photons is too lowe to trigger rotation of water molecules.

Unsuccessful because it caused too much heat and became microwave ovens. Not suitable as a radar device but suitable as a cooking oven.

http://www.zmescience.com/science/physics/microwave-oven-from-ww2/

4. In the short run, air quality causes health issues and affects productivity.

In the long run, we can slow down ozone depletion but not stop it as the chain reaction causes chlorine to be constantly produced. As a result, more UV-vis radiation will penetrate the atmosphere, causing skin cancer and more energy will be reflected. Aquatic life species would be affected by UV rays and there is a possibility of extinction which will lead to imbalance of our ecosystem.

 

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Week 5 Application Exercises

1)

a)Exothermic. The burning of charcoal briquette releases heat during the process.
b) Endothermic – Water absorb the heat energy to evaporate.
c) Endothermic – Ice absorb the heat energy require to melt.

 

2)

ΔHoreaction=∑ΔHof(products)−∑ΔHof(Reactants)

ΔHrxn=ΣΔHbreaking+ΣΔHmakingΔHrxn=ΣBEreactants−ΣBEproducts

Ans: A good explosion would have a very negative enthalpy, which means that the  bond strengths in reactants must be higher than products as you can see from the equation above.

 

3)

Heat is a form of energy transferred from one body to another, from a region of higher temperature to a region of lower temperature.

Temperature is not energy. It is a measure of the degree of hotness or coldness which is measured by different kinds of thermometer.

Q = mcΔT

Q = heat content in Joules

m = mass

c = specific heat, J/g °C

T = temperature

ΔT = change in temperature

Two different substances may have the same temperature but contains different amount of heat as the amount of heat depends on other factors such as mass and specific heat. Hence when a drop of hot water drops on you, you do not feel as pain as compared to a cup of hot water dropping on you as the cup of hot water contains higher mass which result in more heat being transferred to you.

 

 

4)

a) The knocking characteristics of this gasoline is 98% isooctane and 2% heptane.

b) The octane number of the gasoline does not tell us whether or not it contains oxygenates. But,we do know that fuel with oxygenates have higher octane ratings, with common oxygenated fuel additives having octane ratings of over 100.

 

 

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Week 4 – Protecting the Ozone Layer

Today we learnt about some of the advantages and disadvantages of using the term ozone screen as opposed to the term ozone layer to describe ozone in the stratosphere. The term ozone screen will give the misconception that it reflects the UV rays instead of absorbing it. It also gives people an impression that we are totally being screened from the UV rays which is not true.

We also learnt about some of the reasons that the solutions to ozone depletion proposed in the Sydney Harris cartoon will not work. This is because ozone is destroyed and produced at apporoximately the same rate, hence it is difficult to replenish the ozone layer as the rate of it being destroyed will increase.