Category Archives: Research

Process, Research

Application Exercise 7 – The World of Polymers and Plastics

Leave a comment

1) 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 you stretch the plastic bag, the plastic bag narrows and “necks down”. The molecules of the plastic bag will become aligned to each other in a parallel manner and in the direction of the pull. When you alter the molecule alignment, the process is not reversible and will eventually break when it is pulled for a continued period.

However, in the case of the paper, the paper does not react the same way as the plastic bag when it is pulled. When it is pulled, the paper instead tears instead of stretching to any extent. This is because of the cellulose molecules that are held far more rigidly in place in paper that cannot be freely aligned such as the molecules of the plastic bag.

2) 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: Styrofoam packing peanuts are made of 98% air. When it is immersed in the acetone, the acetone will allow the gases of the foaming agent to escape, leaving behind a denser Styrofoam piece. Therefore, it is more solid and much denser because the gases have been removed.

3) 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. Branched LDPE are not packed in a linear or crystal structure. This means that there is less intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. Therefore, LDPE is usually lower in tensile strength but higher ductility. Therefore, it cannot be used in surgical gloves as it is not strong enough and may be too “flimsy” like a plastic bag.

b. Linear HDPE has a low degree of branching and is mostly made up of linear molecules where intermolecular forces are stronger than highly branched polymers. Therefore, HDPE has high tensile strength. However, in order for it to be flexible enough to be used in surgical gloves, only a thin liner of HDPE is used. This ensures the gloves are strong enough to be resistant to cuts and at the same time, flexible enough for use as gloves (fit into surgeons hands, stretched, etc.).

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 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) Non-toxic, (2) Lack of reactivity in body fluids, (3) Lack of solubility in body fluids and (4) stability over time of intended use. We can also consider the costs and the ease of implantation.

b. In the market, there are different types of contact lenses that are made of different kinds of polymers. 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).

c. Polymethyl methacrylate (PMMA) are typically used in hard contact lenses. This is a rigid non-gas permeable plastic which may reduce the oxygen supply to eyes when it is used. On the other hand, soft contact lenses are made of silicone, a flexible and gas permeable plastic. This allows sufficient oxygen to reach the eye, making it more comfortable and less painful on the eyes.

My Work, Process, Research

Application Exercise 5 – Water for Life

Leave a comment
  1. How can you purify your water when you are hiking? Name 2 or 3 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.  3 ways hikers are able to purify water are: boiling water, using filters or purifiers, and using purification tablets (chlorine dioxide tablets).Out of the aforementioned possibilities to purify water on a hike, the cheapest method is most likely boiling water as it uses simple tools such as a tin can to place the water in and fire starters to start the fire. This method requires just 1 to 3 min for the water to be prepared. However, this method wastes fuel in lighting the fire which are essential for cooking.

    Using filters or purifiers does effectively purifiers water obtained from streams or other water bodies easily, but the cost for these equipments may not be cheaply available, although of recent years the equipment have become more affordable.

    Purification tablets is the preferred choice based on efficiency and convenience as the tablets are lightweight and will not take up much space to be carried on a hike. They are also easy to use by just dropping the tablet into the water container and waiting 30 minutes, the water will become drinkable.

  2. Explain why desalination techniques, despite proven technological effectiveness, are not used more widely to produce potable drinking water. Desalination of water is very expensive costing hundreds to thousands of dollars due to the large amount of energy it requires. As salt dissolves very easily, forming strong hydrogen bonds with water, the intermolecular bonds would be difficult to overcome. Expensive technological equipment is another contributing factor to the high costs of desalination technique. It is much cheaper and accessible to use local freshwater especially for the less developed countries whereby amenities are less available.
  3. 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.

    a. Corrosion of lead pipes which transports water to the drinking fountains.

    b. Research activities uses water from a different pipe from drinking water which may not be contaminated with elevated lead levels.

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

Fat-soluble vitamins are non-polar so as to interact with non-polar lipid molecules while water-soluble vitamins would have polar properties enabling interaction with polar water molecules. Similar polarity properties with the solvents are important to allow the vitamins to dissolve and be transported to the respective regions within the body.

 

Process, Research

Application Exercise 4 – Global Warming

Leave a comment
  1. Understanding Earth’s energy balance is essential to understanding the issue of global warming. For example, the solar energy striking Earth’s surface averages 168W/m^2, but the energy leaving Earth’s surface averages 390W/m^2. Why isn’t Earth cooling rapidly?

This phenomenon is also known as “thermal inertia”. This is due to energy being emitted as longwave radiation because the earth and its atmosphere has characteristic temperatures. The Earth stays hot even after energy leaves it’s surface because it’s still emitting the energy it had absorbed earlier.

  1. Decide and explain whether the statement, “This winter has lowered my concerns about global warming”, is correct or incorrect. Explain.

This statement is incorrect as increasing snowfall is actually caused by warmer temperatures due to global warming because more evaporating water from water bodies on earth was available for precipitation.

Cold weather is also due to air moving from higher pressures to lower pressures around the world. Artic oscillations push cold wet and snowy weathers to parts of the earth with lower pressures, resulting in colder winters.

  1. One of the first radar devices developed during the WWII used microwave radiation of a specific wave range that triggers the rotation of water molecules. Why was the design not successful?

Absorption of microwave radiation by water in the atmosphere interferes with the detection of the intended object.

  1. Now that you have studied air quality, stratospheric ozone depletion and global warming, which do you believe poses the most serious problem for you in the short run and in the long run?

In the short run, air quality is believed to pose the most serious problem as it affects the most important human survival necessity, that is to breathe. For example, air pollutions like the haze causing a surge in PSI values would lead to respiratory problems or even death.

In the long run, global warming is believed to pose the most serious problem as it is destructing the planet we all live in. For example, the melting ice caps causing a rise in sea levels leads to floods and droughts. Also, extreme weather conditions and excessive deforestation affects our land and would eventually lead to our planet being unsuitable for human survival.

Process, Research

Application Exercise 3 – Energy from Combustion

Leave a comment
  1. From personal experience, state whether these processes are endothermic or exothermic. Give a reason for each.

a) A charcoal briquette burns.

This reaction is exothermic because hear is released as the charcoal burns. The heat released is used to cook your food!

b) Water evaporates from your skin.

This reaction is endothermic because water (liquid state) absorbs heat from your skin necessary for it to change into water vapour (gaseous state). Therefore, your skin will feel cooler.

c) Ice melts:

The reaction is endothermic as ice (solid state) absorbs heat for it to melt into water (liquid state).

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

In this case, we would consider a natural gas (methane) explosion:

CH4 + 2 O2 –> CO2 + 2 H2O

In this example, the bond energies involve:

-C–H single bonds, 416 kJ/mole

-O=O double bonds, 498 kJ/mole

-H–O single bonds, 467 kJ/mole

-C=O double bonds, 803 kJ/mole

From this, we can see that the energies of the product (CO2 + 2 H20) are larger than those of the reactants. This will lead to a large negative net energy change, thus highly exothermic explosions.

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

Heat is a form of energy while temperature is a measurement indicating the direction of the heat flow. Heat always flows from a hotter object to a colder object. Take for example choosing between spilling a drop of tea on yourself than the whole cup of tea at the same temperature. Even at the same temperature, it will definitely be more painful from the bigger volume of tea because of the higher heat content. Heat depends on the temperature and volume of material. In the case of temperature, when cold water is added to the hot tea, the heat will flow from the hot tea to the cold water and the final temperature of the new mixture will be between that of the original temperatures of the cold water and tea.

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

a) the knocking characteristics of this gasoline?

It has the same knocking characteristics as a mixture made up of 98% isooctane and 2% n-heptane. The word ‘premium’ gasoline would indicate lower knocking characteristics and that this company’s gasoline has a higher octane rating than other gasoline blends sold at other stations.

b) whether the fuel contains oxygenates?

The octane rating does not provide additional information about whether the fuel contains oxygenates. This can be found on other labels around the pump instead.

Featured image link: http://www.iscv.org/tag/energy-use/