Month: March 2017

Unit 7: The World of Polymers and Plastics

Standard

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. The solid still consists of Styrofoam, but now it is solid and much denser. Explain. Hint: Remember that Styrofoam is made with foaming agents.

1) Acetone will dissolve the polymer, allowing the gas of the foaming agent to escape. The polymer collapses on itself and hence is more dense because the gas has been removed

Q2) 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.

2a) LDPE does not have the required strength to be used in this application, hence, it cannot be used in this application.

2b) The molecules of HDPE must line up in a way that produces the required strength. Furthermore, by using a thin liner of HDPE, it allows sufficient flexibility.

Q3) 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.

3) When the piece of plastic is stretched, the strip narrows and “necks down.” The molecules become aligned parallel to each other and in the direction of the pull. This alteration of the three-dimensional structure is not reversible, and if the pulling continues, the plastic breaks. When the same pulling force is applied to a piece of paper, the paper tears rather than stretching to any significant extent. The cellulose molecules in paper are held far more rigidly in place, and are not free to become aligned.

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 bio compatible 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?

4a) The benefits for polymers intended for use in the body should far outweigh any risks. The two main properties are (1) stable over time of intended use and (2) non-toxic. Other factors to consider are low cost, lack of solubility in body fluids, lack of reactivity in body fluids, and the ease of implantation

4b) Several different types of contact lenses are on the market and each uses a different type of polymer. Polymethyl methacrylate (PMMA), one of the earliest polymers used for rigid gas permeable lenses, is structurally similar to Lucite and plexiglas. Silicone-acrylate materials now are more commonly used under trade names such as Kolfocon. Newer rigid gas permeable (RGP) polymers contain fluorine: fluoro-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). Manufacturers’ websites are good sources of information. 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 (if not disposable).

4c) As mentioned in the previous part, 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.

 

Unit 6: Neutralising the Threat of Acid Rain

Standard

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

b) The NCPA 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.

1a) Coal-fired plants release sulphur dioxide which creates sulphate particles theatre responsible for 60 – 85% of poor visibility in eastern parks.

1b) Normal rain has a pH range of 5 – 6. If the rainfall in the park is 10 times more acidic, the pH range must be in the range of 4 – 5.

Q2) Here are some 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 transport 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.

2a) Laundry can be dried using a electricity dryer. Electricity is generated at power stations by electro-mechanical generator. It is driven by heat engines which is produced by fossil fuel. Fossil fuel burning will results in SOX being released into the atmosphere. Therefore, hanging your laundry to dry phase out the need of electricity usage.

2b) The amount of NOx generated will be reduced if everyone takes public transport instead of driving their own vehicles. As NOx is one of the components of acid rain, reducing the NOx emissions would help in controlling the pH level of the rain.

2c) These appliances use electricity which are generated by power-supply plants which burn coal. It will leads to the emission of sulfur dioxide which contributes to acid rain.

2d) With the additional insulation on hot water heater and pipes, it helps to reduce heat loss to the surrounding. Therefore, less energy is needed to heat up the system. With a lower energy consumption, lesser coal will be burnt and hence a lesser amount of SOx gas will be formed.

2e) Through buying local products, it means a lower demand for goods that are overseas. This means that there is a lower need for transport vehicles such as airplanes and ships to be used to transport products from other parts of the world. It helps to reduce the amount of NOx gas produced by the engines of these vehicles during transportation which will add to the formation of acid rain.

Q3a) Give names and chemical formulas for five acids and five bases.

Q3b) Name three observable properties generally associated with acids and bases.

3a) Acids:

Hydrochloric Acid (HCl)
Nitric Acid (HNO3)
Phosphoric Acid (H3PO4)
Hydroiodic Aacid (HI)
Hydrobromic Acid (HBr)

Bases:

Ammonia (NH3)
Sodium Hydroxide (NaOH)
Calcium Hydroxide (Ca(OH)2)
Lithium Hydroxide (LiOH)
Potassium Hydroxide (KOH)

3b) Acid tastes sour, turns blue litmus paper red, and releases carbon dioxide from carbonates. Bases taste bitter, turns red litmus paper blue, and have a slippery feel in water.

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 the Singapore’s borders?

4) I believe the acid deposition originated from both outside and inside of Singapore border.

The lower in the pH level in various location in Singapore is mainly due to the industrial activities. The burning of fossil fuels by the industrial and power plants releases sulfur into the atmosphere which combines with oxygen to form sulfur dioxide. This contributes to the increased in the acid level in various locations in Singapore.

The haze issue caused by our neighboring countries also contributed to the acid deposition of Singapore. Haze contains aerosols which allows the formation of acid rain. It leads to the increased in the acidity in the water bodies of Singapore.