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Unit 7: Application Exercise 7

  • 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.

Answer:

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

 

  • 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. LDPE cannot be used in this application because it does not have required strength.

b. The molecules of HDPE must line up in a way that produces the required strength. Using a thin linear of HDPE allows sufficient flexibility.

 

  • 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:

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.

 

  • 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. (1) Stable over time of intended use, (2) non-toxic, (3) ease of implantation, (4) low cost.

b. 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 plexiglass. 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). Desirable properties include being non-toxic, permeable to oxygen, comfortable to wear, and not expensive. The ability to conform to the shape of the eye and to be easily cleaned are also desirable.

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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Unit 5: Application Exercise

Q1) How can you purify your water when you are hiking? Name two or three possibilities. Compare these methods in terms of cost and effectiveness. Are any of these methods similar to those used to purify municipal water supplies? Explain.

There are many options to purify water while hiking.

  • Boiling

– Boiling is the most certain way of killing all microorganisms. According to the Wilderness Medical Society, water temperatures above 160 degree F kill all pathogens within 30 minutes and above 185 degrees F, within a few minutes. So by the time it takes for the water to reach the boiling point from 160 degrees F, all pathogens will be killed, even at high altitude. To be extra safe, let the water boil rapidly for one minute, especially at higher altitudes since water boils at a lower temperature.

– Boiling however requires time and does not remove chemical contamination. It also requires fuel and may release soot and carbon dioxide to the atmosphere.

  • Iodine Treatment

– Iodine is light sensitive and must always be stored in a dark bottle. It works best if the water is over 68 degrees F. Iodine has been shown to be more effect than chlorine-based treatments in inactivating Giardia cysts. However, some people may be allergic to iodine and cannot be used for water purification. Persons with thyroid problems or on lithum, women over fifty, and pregnant women should consult their physician prior to using iodine for purification. Also, some people who are allergic to shellfish are also allergic to iodine. If someone cannot use iodine, use either a chlorine-based product or a non-iodine-based filter.

– Iodine is easy and effective in around twenty minutes, but iodine should not be used long term. While iodine renders water bacteriologically safe, it does not remove chemical contaminations. Many people also dislike the taste of iodine-treated water.

  • Filtering device

– Filtration has the advantage that it does not require chemicals and removes many of the organisms not killed by boiling or iodine treatment.

– Filters are the most expensive option, a good filter pumps out good water in a few minutes and is reusable.

Municipal water preparation involves coagulation, sedimentation, filtration, and disinfection. Obviously more comprehensive, but like during hiking involves both filtration and disinfection – mainly chlorination.

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

Most common desalination techniques are reverse osmosis and distillation. However, both of these require a large amount of energy to salts from seawater or brackish water and thus are expensive methods. If a less expensive option is available such as hauling fresh water from a distance, then this option is used.

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.

 

  • The likely source of lead is from solder in the pipe joints or from lead pipes themselves.

  • Research activities should not contribute to lead in the drinking water, assuming that any lead compounds are not dumped down the drain. Most chemistry experiments especially at the undergraduate level have been redesigned and do not involve lead compounds and other toxic metal ions. Recall that 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.

Only water-soluble vitamins would be expected to be polar molecules. Though a fat-soluble vitamin will often have individual polar bonds or small regions of the molecule, overall this is outweighed by nonpolar sections. Polar covalent bonds attract to water through hydrogen bonding and may allow the molecules to dissolve in water, while nonpolar covalent bonds favour interactions with the nonpolar chains in lipids.

 

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Unit 4: Application Exercises

Today’s topic is about energy.

These are the application questions cool

State whether these processes are endothermic or exothermic. Give a reason for each.

Burning a charcoal briquette.

Burning a charcoal briquette is an exothermic process because heat is generated.

Water evaporating from your skin

This is an endothermic process as heat is absorbed from the skin and used to break the inter molecular bond between the water molecules so that water can evaporate.

Ice melting 

Ice melting is an endothermic process as energy is absorbed to break inter molecular bonds between water molecues.

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

An energy level diagram showing an exothermic reaction

From the figure above we can see that the energy level of the reactants are higher than that of the products. Bond breaking is an endothermic process while bond forming is a exothermic process. Since the overall reaction is exothermic the energy released by bond forming would be greater than energy absorbed by bond breaking. Hence the bond strength of the products would be stronger.

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

In scientific terms, heat is the total measure of the motion of molecules in a substance while temperature is the average energy of molecular motion in a substance. However this doesn’t really tell you the difference

Consider a small cup of hot water and a large tub of hot water. Both have the same temperature. However the large tub of water has more heat. The large tub of water contains the molecules with the same energy as the small cup but since the large tub has more molecules it has more energy and hence more heat.

In short temperature is not energy but a measure of it. Heat is energy.

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

An octane rating of 98 means that that the fuel acts similarly to a fuel that is 98% resistant to knocking.

The octane rating does not tell us any information about whether the fuel contains oxygenates.

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Unit 3: Application Exercise

Application Exercise 4

Q1. Understanding Earth’s energy balance is essential to understanding the issue of global warming. For example, the solar energy striking Earth’s surface averages 168 watts per square meter (W/m²), but the energy leaving Earth’s surface averages 390 W/m²Why isn’t Earth cooling rapidly?

The amount of energy emitted by the Earth’s surface is more than double of the incident solar energy on the Earth as the atmosphere absorbs and retains this emitted heat energy, keeping the Earth’s energy balanced.

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

The stamen is incorrect. Weather is measured over minutes, hours, days or seasons while climate change is measured over a period of more than 30 years. Hence, a lower temperature during the winter does not mean that the Earth is cooling.

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?

The atmospheric water molecules surrounding the radar devices absorbed the microwave radiation, triggering the molecules to rotate rapidly and converting electrostatic potential energy to thermal energy. This interfered with the detection of intended objects, making the radar devices pointless.

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)?

In the short run, deteriorating air quality will be of the largest concern. Worsening air pollution (eg. haze) affects us directly as it leads to health problems such as cardiovascular and respiratory problems.

In the long run, depleting stratospheric ozone will be the most severe problem. As the ozone layer depletes, more UV rays penetrate and reach the Earth’s surface. Exposure to higher amounts of UV radiation leads to irreparable damage to the ecosystem. For example, the human health is adversely affected through increased risk of skin cancer, cataracts and weakening immune system; reduced agriculture as crops are more vulnerable to increased UV radiation; threatening of marine life and animals due to disruptions in food chains and reproduction cycles.