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.

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.

1) Method 1: Boiling 

Boiling kills many microorganisms that cause illness. However, it requires time and will not remove chemical contamination. Boiling requires fuel and releases soot and CO2 to the environment. 

Method 2: Iodine

iodine is easy and effective in twenty minutes, but it should not be for long term usage. In addition, pregnant women and people with thyroid conditions should avoid purification with iodine. However, it does not remove chemical contamination. Many people dislike the taste of iodine-treated water. 

Method 3: Household bleach

A small amount of household bleach can be used to kill some but not all microorganisms in the water. Again, many people dislike the resulting taste.

Municipal water preparation applies a combination of methods which involves coagulation, sedimentation, filtration, and disinfection. It is a much more comprehensive process. It involves both disinfection and filtration which deal with the chlorination of the water. 

Q2) Explain why desalination techniques, despite proven technological effectiveness, are not used more widely to produce potable drinking water.

2) Distillation and reverse osmosis are two most common desalination techniques. Both require huge amount of energy to remove salts from seawater or brackish water, and thus inherently are expensive. 

Q3) Water quality in a chemical engineering building on campus was continuously monitored because testing indicated water from drinking fountains in the building had dissolved lead levels above those established by NEA.

a) What is the likely major source of the lead in the drinking water?

b) Do the research activities carried out in this chemistry building account for the elevated lead levels found in the drinking water? Explain.

3a) The likely major source of the lead in the drinking water:

• Solder in the pipe joints
• From the lead pipes themselves

3b) Research activities should not account for the elevated lead levels found in the drinking water, assuming that no lead compounds are discharged into the sewage system. Most of the modern undergraduate chemistry experiments have been redesigned to avoid having lead compounds and other toxic metal ions. The substances dumped into a sewage treatment system may end up downstream in someone else’s drinking water. 

Q4) Some vitamins are water-soluble, whereas others are fat-soluble. Would you expect either or both to be polar compounds? Explain.

4) Only water-soluble vitamins would be expected to be polar molecules. Even though a fat-soluble vitamin often have individual polar bonds or small regions of the molecule, overall it is out-weighed by non-polar sections. Polar covalent bonds are attracted to water through hydrogen bonding and may allow the molecules to dissolve in water. On the other hand, non-polar covalent bonds prefers interactions with the non-polar chains in lipids.

1) Earth does not cool rapidly even though the amount of energy emitted is greater than double the amount received. It is because the atmosphere retains much of the emitted heat energy.

Q2) “This winter has lowered my concerns about global warming…”. Decide and explain where the stamen is correct or incorrect. Explain.

2) The quote “This winter has lowered my concerns about global warming…” is not validated. It actually meant to poke fun at people who have no clue about global warming and do not understand the different between weather and climate.  It does not meant the earth is getting colder just because there are there are particular seasons in regions that are cold, like winter. Measure of time is the key difference that set apart weather and climate. Climate refers to the typical and average weather a region will have over a lengthy period of time. Therefore, scientists use climate for statistics about the temperature of earth. It helps to determine whether earth is getting warmer or colder. Weather as compared to climate is not that reliable. It is nothing more than the atmosphere condition over a brief period of time.

Q3) One of the first radar devices developed during World War II used microwave radiation of a specific wave range that triggers the rotation of water molecules. Why was the design not successful?

3) The design was not successful because of the following reasons:

• It heated up the air around the machine.
• It caused diseases in the radar operators.
• Water absorbed the microwave radiation in the atmosphere interferes with the detection of intended objects.

Q4) Now that you have studied air quality (Unit 1), stratospheric ozone depletion (Unit 2), and global warming (Unit 3), which do you believe poses the most serious problem for you in the short run (pick one and explain)? In the long run (pick one and explain why)?

4) The answers will be geographically influenced. Students will most likely be concerned of air quality as the most severe problem in short term, especially those living in and around large cities. The ozone hole is probably too far removed to affect most students directly. Depending on the students’ perceptions of the seriousness of climate change, that will most likely be their most serious long-term concern.

a) Burning a charcoal briquette

b) Water evaporating from your skin

c) Ice melting

1a) Exothermic. A charcoal briquette releases heat as it burns.

1b) Endothermic. Water absorbs the heat needed for evaporation from your skin and hence your skin feels cooler.

1c) Endothermic. Ice absorbs the necessary heat to melt from the surrounding environment.

Q2) Chemical explosions are very exothermic reactions. Describe the relative bond strengths in the reactants and products that would make for a good explosion.

2) The products’s bond energies are larger that those of the reactants. This will lead to a negative net energy change resulting a large exothermic reaction. Thereby making it suitable for a good explosion.

Q3) How might you explain the differences between temperature and heat to a friend? Use some practical, everyday examples.

3) I would explain to him by saying the following:

Would you rather spill a drop of hot soup on yourself or a whole bowl of it at the same temperature. Though the drop and the bowl of hot soup are of the same temperature, you will get a bigger burn from the greater volume of the soup because it is of higher heat content. Heat is a form of energy. It always flows from a point of higher temperature to a point of lower temperature. On the other hand, temperature is a unit of measurement that indicates the direction heat will flow.

Q4) A premium gasoline available at most stations has an octane rating of 98. What does that tell you about:

a) the knocking characteristics of this gasoline?

b) whether the fuel contains oxygenates

4a) Gasoline with 92 as its octane rating shares the same knocking characteristics as a mixture that is made up of 92% isooctane and 8% heptane. Therefore, it is resistant to knocking.

4b) The octane rating does not provides any information if the fuel contains any oxygenates. Other labels around the pump should show this piece of information instead.

The air that we are breathing is not pure but it is a mixture.

Suspended particulate matter in the air in high concentration can cause serious damage to human body.