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Q1) When Styrofoam packing peanuts are immersed in acetone (the primary component in some nail-polish removers), they dissolve. If the acetone is allowed to evaporate, a solid remains. This solid still consists of Styrofoam, but now it is solid and much denser. Explain. (Hint: Remember that Styrofoam is made with foaming agents)

Answer:

Acetone dissolves the polymer (Styrofoam), allowing the foaming agent to escape. Once the acetone has evaporated, the polymer remains and is now solid and more dense than before as it has collapsed due to the lack of foaming agent.

 

Q2) Consider Spectra, Allied-Signal Corporation’s HDPE fibre, 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 very 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.

Answer:

LDPE does not have the required strength to resist being accidentally cut during surgery.

 

B) Offer a molecular-level reason for why linear HDPE is successful in this application.

Answer:

As the arrangement of molecules affects the material’s flexibility, the arrangement of molecules in a linear fashion offers the material sufficient flexibility.

 

Q4) When you try to stretch a 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:

When the plastic bag is stretched, it necks and narrows down. Molecules become aligned parallel to each other and in the direction of the pull. When stretching paper in the same way, however, it does not stretch but breaks instead. This is due to the molecules in the cellulose in paper being arranged in a more rigid way that does not permit the molecules to be re-aligned like in the case of the plastic bag.

 

Q5) Some polymers are biocompatible and now used to repair human body parts.

A) List 4 properties that would be desirable for polymers used within the human body.

Answers:

The materials should be non-toxic, should not degrade over time, easy to transplant into the body, and does not react with body tissues and fluids.

 

B) Other polymers may be used outside the body, but in close contact with it. For example, a surgeon is not needed to use contact lenses- they can be removed, stored, and cleaned 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.

Answers:

Polymethyl methacrylate (PMMA), polyacrylamide, and rigid gas permeable (RGP) polymers. Properties desirable in these materials include: does not react with substances on the eye surface, permeable to oxygen so as to allow oxygen to reach the eyeball, easy to manufacture, comfortable to wear, and easily deformable so as conform to the shape of the eyeball. Ease of cleaning is also important for reusable contact lenses.

 

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 contact lenses?

Answers:

“Hard” lenses are usually made of PMMA, which was more rigid and non gas-permeable. “Soft” lenses are made of silicone, PMMA and fluoruopolymers, which is more flexible and allowed oxygen to permeate through it to reach the eyeball. The soft lenses may be more comfortable due to these properties.

 

References

  1. Polymers in everyday things- contact lenses [PDF]. (n.d.). RSC. http://www.rsc.org/Education/Teachers/Resources/Inspirational/resources/3.1.1.pdf

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Q1) Mammoth Cave National Park in Kentucky is in close proximity to the coal-fired electric utility plants in the 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?

Answer:

Coal-fired power plants generate sulphuric acid which reduces visibility especially in the summer months when there is more sunlight. This is because the sulphuric acid forms small droplets which in turn form aerosols that reflect sunlight rather than absorb it, reducing visibility.

B) The NPCA reported that “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 the rainfall in the park.

Answer: 

Normal rain is slightly acidic, about pH 5.3. This means that the pH of the rain in Mammoth Cave is 4.3. This is because a decrease of 1 on the pH scale, which is a logarithmic scale, corresponds to two substances differing in H+ concentration by 10 times.

 

Q2) Here are some examples of what an individual might do to reduce acid rain. For each, explain the connection to producing acid rain.

Answers:

A) Hang your laundry to dry it.

Drying laundry via hanging eliminates the need to generate additional energy in order to operate clothes dryers. This means less energy will be needed to be generated via coal, decreasing the SOx emissions from coal-fired power plants. SOx emissions contribute to acid rain, so decreasing their emissions would regulate the pH of rain.

B) Walk, bike, or take public transportation to work.

This reduces the amount of NOx generated by vehicles as compared to everyone taking public transport. Since NOx emissions also contribute to acid rain, reducing NOx emissions would also help in regulating the pH of rain.

C) Avoid running dishwashers and washing machines with small loads.

Not maximising the capacity of the machine results in an inefficient use of energy, which means there is wastage of energy generated via coal. Since generating energy via coal results in SOx emissions into the atmosphere, it is important to make sure any energy is used efficiently.

D) Add additional insulation on hot water heaters and pipes.

Adding additional insulation prevents heat from the water from escaping into the environment easily. This reduces the need to reheat water that has lost heat due to lack of insulation. Extra energy is thus not used to reheat the water, reducing the need for energy via coal-fired power plants that emit SOx into the atmosphere.

E) Buy locally grown produce and locally produced food.

This reduces the amount of energy needed to transport food from farm to table. Imported food needs to travel a longer distance to reach us and the extra NOx and SOx generated to provide energy to transport the food over longer distances can contribute to acid rain.

 

Q3)

A) Give names and chemical formulas for 5 acids and 5 bases.

Answer:

Acids:

  1. H2SO4 Sulphuric acid
  2. HCl Hydrochloric acid
  3. H3PO4 Phosphoric acid
  4. HNO3 Nitric acid
  5. H2CO3 Carbonic acid

Bases:

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

B) Name three observable properties generally associated with acids and bases.

  • Acids: have a sour taste, turns blue litmus paper red, turns phenolphthalein colorless
  • Bases: have a bitter taste, turns red litmus paper blue, turns phenolphthalein pink

 

Q4) 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 Singapore’s borders?

Answer:

Some issues in Singapore could include health hazards such as haze, and infrastructure issues when acid rain comes into contact with buildings, where money could be involved to repair the infrastructure. Also, the biodiversity of animals could be affected due to acid rain, as most aquatic animals cannot survive below pH 5. Singapore has several fish farms, and a decrease in pH could affect the fish in the water.

Our group thinks that acid deposition originates from both inside and outside Singapore. For example, in the case of haze, the acid deposition originated from outside Singapore. However, acid deposition originating inside Singapore could come from sources such as Jurong Island, where there are refineries, and car exhausts from our transport systems.

 

References:

  1. Gunasingham, A. (2009, September 14). Native species in Singapore may be wiped out by acid rain. Retrieved March 16, 2017, from http://wildsingaporenews.blogspot.sg/2009/09/native-species-in-singapore-may-be.html#.WMjlNu5EmM8