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 agent.

Dissolving the polymer in acetone allows the gas of the foaming agent to escape. After the removal of gas, the polymer collapses on itself and becomes denser.

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.

It does not have the required strength.

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

The molecules of HDPE must line up in a way that produces the required strength. Using a thin liner of HDPE 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.

Stretching of the plastic bag cause the plastic strip to narrow and “neck down”. The alignment of molecules cause them to be parallel to each other and in the direction of the pull. This alteration of the 3D structure is irreversible, and would cause the plastic to break if the pulling continues. 

When the same pulling force is applied to a piece of paper, the paper will tear instead.  This is because the cellulose molecules in paper are held far more rigidly in place and hence unable to be moved to align.

Q4. 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 

1. stable over time of intended use

2. non-toxic

3. low cost

4. lack of solubility and reactivity in body fluids

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.

There are several different types of contact lenses on the market which uses different types of polymer. Polymethyl methacrylate (PMMA) is one of the earliest polymers used for rigid gas permeable lenses. Currently, Kolfocon is the commonly used trade name for silicone-acrylate materials. 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). These materials have desirable properties such as being non-toxic, permeable to oxygen, comfortable to wear, and inexpensive. Other important quality include the ability to conform to the eye shape and easily cleaned.

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?

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

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?

Coal-fired plants release sulphur dioxide, creating sulphate particles that are responsible for 60 to 85% of the poor visibility in eastern parks.

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.

Normal rain has a pH range of 5–6, so if the rainfall in this park is 10 times more acidic, the pH range must be 4–5 since pH is a log scale based on 10, a pH change of 1 unit represents a power of 10 change in [H+].

Q2. 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.

Hanging laundry to dry requires less energy than using a electric dryer. Cutting down on energy use cuts down on the need for power companies to produce electricity by burning coal, hence decrease the amount of SO2 emission thus decrease the production of acid rain.

b. Walk, bike, or take public transportation to work.

All of these transportation method reduces the amount of gasoline (or other energy source) used, cutting down on NO emissions and thus contributing less to the acidity of the rain.

c. Avoid running dishwashers and washing machines with small loads.

 Avoid running dishwashers and washing machines with small loads will reduce cutting down on energy use cuts down on the need for power companies to produce electricity by burning coal, hence decrease the amount of SO2 emission thus decrease the production of acid rain.

d. Add additional insulation on hot water heaters and pipes.

Reduce heat loss of the hot  water heater and pipes hence reducing extra energy used to keep water hot. This will decrease the need to produce electricity by burning coal, hence decrease the amount of SO2 emission thus decrease the production of acid rain.

e. Buy locally grown produce and locally produced food.

Buying locally grown produce can decrease the sale of industrial food production which is mostly dependent on fossil fuels when refined and burned can emit SO2 and NO which is the main cause of acid rain.

Q3.

a. Give names and chemical formulas for five acids and five bases.

Acids:

Sulphuric acid (H₂SO₄)

Nitric acid  (HNO₃)

Chromic acid (H₂CrO₄)

Boric acid (H₃BO₃)

Acetic acid (CH₃COOH)

Bases:

Lithium hydroxide (LiOH)

Sodium hydroxide (NaOH)

Potassium hydroxide (KOH)

Calcium hydroxide (Ca(OH)2)

Barium hydroxide (Ba(OH)2)

b. Name three observable properties generally associated with acids and bases.

Acids are sour while Bases are bitter.

Acid turn blue litmus paper red while Bases turn red litmus paper blue.

Both acid and bases conduct electricity.

Q4. The concern of acid rain vary across the globe. Many countries in North America and Europe have websites dealing with acid rain. Either search to locate (“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?

Issues in Singapore:

Haze- Forest burning from neighbouring country

Increase in mean temperature

Rising sea level

The acid deposition originate both inside and outside of Singapore’s border. However, the extent of acid deposition is higher outside of  Singapore’s border.

Acid deposition originate from the inside of Singapore due to the factories that emits SO2 and NO gases as they burn coals for energy but this is a small amount because the government set regulation to control the amount of harmful gases emitted.

Acid deposition originate from the outside of Singapore’s border such as forest burning in Indonesia which releases harmful gases that can lead to acid rain. This is a more serious problem because the authorities in the country do not regulate the amount of harmful gases emitted hence the acid deposition is more serious outside Singapore.