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AE 7: The World of Polymers and Plastics

Source: https://i.ytimg.com/vi/YcLS_FF6wfs/maxresdefault.jpg

1. When Styrofoam packing peanuts are immersed in acetone, they dissolve. If the acetone is allowed to evaporate, a solid remains. The Solid still consists of Styrofoam, but now it is solid and much denser. Explain.

Answer: Styrofoam is composed of 98% air. When polystyrene dissolves in acetone, the air in the foam is released, thus compacting the Styrofoam into a solid which is much denser.

2. Consider Spectra, Allied-Signal Corporation’s HDPE fiber, used as liners for surgical gloves. Although the Spectra liner has a very high resistance to being cut, the polymer allows a surgeon to maintain a delicate sense of touch. The interesting thing is that Spectra is linear HDPE, which is usually associated with being rigid and not very flexible.

a. Suggest a reason why branched LDPE cannot be used in this application.

b. Offer a molecular level reason for why linear HDPE is successful in this application.

Answer:

a. Branched LDPE are softer and more flexible but have lower tensile strength, thus, during a surgery, it may break easily exposing surgeons to viruses or bacteria present.

b. The polymer chains in HDPE, on the other hand, are more linear. They pack closer together, resulting in greater intermolecular forces and a more “crystalline” structure. HDPE has greater tensile strength than LDPE.

3. When you try to stretch a piece of plastic bag, the length of the piece of plastic being pulled increases dramatically and the thickness decreases. Does the same thing happen when you pull on a piece of paper? Why or why not? Explain on a molecular level.

Answer: No it does not happen to paper. For plastic bags, the molecules are packed together with high degree of branching, thus creating a less strong intermolecular forces which results in lower tensile strength and increased ductility. This happens in the opposite manner for paper whereby paper has a low ductility characteristic.

4. A Teflon ear bone, fallopian tube, or heart valve? A Gore-Tex implant for the face or to repair a hernia? Some polymers are biocompatible and now used to replace or repair body parts.

a. List four properties that would be desirable for polymers used within the human body.

b. Other polymers may be used outside your body, but in close contact with it. For example, no surgeon is needed for you to use your contact lenses—you insert, remove, clean, and store them yourself. From which polymers are contact lenses made? What properties are desirable in these materials? Either a call to an optometrist or a search on the Web may provide some answers.

c. What is the difference in the material used in “hard” and “soft” contact lenses? How do the differences in properties affect the ease of wearing of contact lenses?

Answer:

a. The properties are (1) stable over time of intended use, (2) non-toxic, (3) inert and (4) light. Other factors to consider are low cost, lack of solubility in body fluids, and the ease of implantation.

b. Polymethyl methacrylate (PMMA), one of the earliest polymers used for rigid gas permeable lenses. Silicone-acrylate materials now are more commonly used under trade names such as Kolfocon. Desirable properties include being nontoxic, permeable to oxygen, comfortable to wear, and inexpensive. Also desirable is the ability to conform to the shape of the eye and to be easily cleaned.

c. Hard contact lenses are typically made of PMMA, a rigid non-gas permeable plastic. The soft contact lenses that replaced them are made of silicone, which is flexible and allows oxygen to reach the eye. Because of these properties, the soft lenses tend to be more comfortable.

 

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AE 6: Neutralising the Threat of Acid Rain

Source: http://www.conserve-energy-future.com/wp-content/uploads/2013/04/Deforestation_ForestDamage.jpg

1. Mammoth Cave National Park in Kentucky is in close proximity to the coal-fired electric utility plants in Ohio Valley. Noting this, the National Parks Conservation Association (NPCA) reported that this national park had the poorest visibility of any in the country.

a) What is the connection between coal-fired plants and poor visibility.
b) The NPCA reported “the average rainfall in Mammoth Cave National Park is 10 times more acidic than natural.” From this information and that in your text, estimate the pH of rainfall in the park.

Answer:

a) Coal-fire plants produce sulphur dioxide creating sulfate particles which is responsible for the poor visibility.

b) Normal rain pH is about 5-6 pH. If the average rainfall in Mammoth Cave National Park is 10 times more acidic, this means that the pH of the rainfall is 4-5 pH.

2.Here are examples of what an individual might do to reduce acid rain. For each, explain the connection to producing acid rain.

a) Hang your laundry to dry it.
b) Walk, bike, or take public transportation to work.
c) Avoid running dishwashers and washing machines with small loads.
d) Add additional insulation on hot water heaters and pipes.
e) Buy locally grown produce and locally produced food.

Answer:

a) Water evaporates from the clothes which in turn produces water vapour. H2O combines with SOx and NOx in the air to produce H2SO4 and HNO3 (Acid rain).

b) Public transportation produces NOx from the exhaust which dissolves with H2O in the air to form HNO3 which in turn contribute to the possibility of acid rain.

c) The amount of electricity needed to run dishwashers and washing machines does not change with the amount of load. As such, more fuel is required to run the machines and in turn produces compounds which contribute to the formation of acid rain.

d) With additional insulation on hot water heaters and pipes, this increases the efficiency of the heat systems as there will be lesser heat loss to the surroundings. As such, lesser fuel is required to compensate for the negligible heat loss.

e) Buying local food, this amounts to lesser import by plane or ships. This results in less fuel burnt to run the planes and ships and thus, reducing the chance of acid rain formation.

3. a). Give names and chemical formulas for five acids and five bases.
     b). Name three observable properties generally associated with acids and bases.

Answer:
a)

Acid

 Base
Hydrochloric Acid (HCl) Ammonia (NH3)
Sulphuric Acid (H2SO4) Sodium Hydroxide (NaOH)
Nitric Acid (HNO3) Magnesium Hydroxide (Mg(OH)2)
Phosphorus Acid (H2PO4) Ammonium Hydroxide (NH4OH)
Sulphurous Acid (H2SO3)

Calcium Hydroxide (Ca(OH)2)

b)
1. Acids turn blue litmus paper red.
2. Bases turn red litmus paper blue.
3. When acid reacts with an active metal, effervescence is observed and gas evolved will extinguish a lighted splint with a ‘pop’ sound.
4. Bases feel slippery and soapy.

4. The concerns of acid rain vary across the globe. Many countries in North America and Europe have websites dealing with acid rain. Either search to locate one (“Canada, acid rain”) or use these links to websites in Canada, the UK, or Europe. What are the issues in Singapore? Does the acid deposition originate outside or inside the Singapore’s borders?

Answer:

In the course of pursuit for industrialization to reach a level of development, many Asian nations emphasized on economic development, coupled with the high rate of population growth stemming from an already large population base, guarantees that SO2 and NOx emissions will increase significantly. This is because technology is emerging at a rapid rate, cutting the need for manpower and in turn, increasing the usage of machines.

As atmospheric contaminant are able to be transported over a long distance before it is being deposited, atmospheric pollution and acidification in Asia is a cause of concern to the Singapore Environment.