Session 9: Unit 9 – Molecules and Drugs
1) In allergy sufferers, histamine causes runny noses, red eyes and other symptoms. Here is its structural formula.
a) Give the chemical formula for this compound.
C5H9N3
b) Circle the amine functional groups in histamine.
(in red)
c) Which part (or parts) of the molecule make the compound water-soluble?
(in blue)
2)
3)
4)
Session 7: Unit 8 – The World of Polymers and Plastics
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.
Reason being that acetone will dissolve the polymer which lets the gas of the foaming agent to evaporate. Now that the gas has evaporated, the polymer collapses on itself and becomes more dense.
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.
Branched LDPE can not be used in this application because 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.
When plastic is stretched the molecules in the plastic become aligned parallel to each other in the direction in which it is pulled. This effect is irreversible and any continued pulling will cause the plastic to eventually break. However, when this is done to paper, the paper tears and does not undergo any stretching. This is due to the cellulose molecules in the paper being held rigidly together. Hence, they are not free to become aligned.
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.
The four main properties are:
(1) It will be stable over time of intended use
(2) It is non-toxic.
(3)
(4)
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.
One of the earliest polymers used for rigid gas permeable lenses is Polymethyl methacrylate (PMMA), it 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. 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 usually made of PMMA which is a rigid non-gas permeable plastic and the soft contact lenses that replaced the hard ones are made of silicone, which is more flexible and allows oxygen in the eye. Comparing the properties of the two lenses, obviously the soft lenses will be more comfortable.
Session 6: Unit 6 – Neutralising the Threat of Acid Rain
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 sulfur dioxide which creates sulfate particles that are responsible for approximately 60 to 85 percent of the poor visibility in the park.
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.
A normal rain has a pH range between 5-6, so if the rainfall in this park is 10 times more acidic, the pH range must be between 4-5.
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 – This eliminates the need to use a dryer which consumes a large amount of electricity to generate heat. As a result, carbon emission would be reduced and hence reducing the occurrence of acid rain. This is because carbon dioxide can dissolve in rain water to form carbonic acid, which contributes to the formation of acid rain.
b) Walk, bike, or take public transport to work – These effectively reduce carbon emission and formation of nitrogen oxides. Nitrogen oxide gases are usually produced from the reaction of nitrogen and oxygen during combustion of fuels in air, especially at high temperatures in car engines. This reduces the formation of acid rain as nitrogen oxide is a main contributor in the formation of acid rain.
c) Avoid running dishwashers and washing machines with small loads – More chores could be finished with less electricity wasted. Hence, this increase in effectiveness reduces carbon emission and hence the formation of acid rain, due to the reduction in carbonic acid production.
d) Add additional insulation on hot water heater and pipes – Additional insulation improves the efficiency of heat transfer and less electricity will be required to heat up the water. As a result, carbon emission is reduced and hence the formation of acid rain is reduced too.
e) Buy locally grown produce and locally produced food – Eliminates the need for long-distance transportation, which requires large amounts of fuel during transportation and thus produces high amounts of carbon emission. This effectively reduces acid rain.
Q3a) Give names and chemical formulas for five acids and five bases.
- Acids:
- Hydrochloric Acid (HCl)
- Sulfuric Acid (H2SO4)
- Sulfurous Acid (H2SO3)
- Phosphoric Acid (H3PO4)
- Carbonic Acid (H2CO3)
- Bases:
- Sodium Hydroxide (NaOH)
- Magnesium Hydroxide (Mg(OH)2)
- Potassium Hydroxide (KOH)
- Calcium Hydroxide (Ca(OH)2)
- Ammonium Hydroxide (NH4OH)
b) Name three observable properties generally associated with acids and bases:
- Acids:
- Taste sour
- Turn litmus paper red
- Corrosive to metals
- Bases:
- Taste bitter
- turn litmus paper blue
- Caustic to skin
Q4)
Acid rain could be driving Singapore’s remaining native species to extinction. For example, twenty species of animals plentiful in the Bukit Timah Nature Reserve in the 1980s, including frogs, crabs and fish, are slowly being wiped out.
Acid rain is formed both within and outside of Singapore.
Sulphur dioxide is a toxic gas and contributes to acid rain. The local emitters of sulphur dioxide include motor vehicles, refineries, power stations, shipping and other industries.
External sources of acid rain include forest fires in Indonesia causing severe air pollution in Singapore. Forest fires produce carbon dioxide and sulphur dioxide, which combines with rain to make carbonic acid and sulphuric acid.
Session 5: Unit 5 – Water for Life
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.
The first and direct method to purify water is to boil it. While boiling kills microorganisms that are present in the water, it’s unable to remove the chemical contamination within the water. In addition boiling requires time, heat source and may release pollutants such as soot and CO in the process.
Second method is to purify water with iodine. This method is not time consuming unlike boiling. However iodine is not recommended for long term use. Furthermore, people with thyroid problems and pregnant women are discouraged from using iodine. Also similar to boiling, iodine does not remove chemical contamination although it renders the water bacteriologically safe.
The third method is adding a small amount of household bleach. This method kills some microorganisms but is unable to kill all. Therefore it is not 100% effective.
The last method is mechanical filtration. Many manufacturers currently manufacture travel water filters with varying degrees of effectiveness. This method does not require the use of chemicals which is its main advantage. Although filters are expensive, they are the most effective way to filter water and are also reusable. Also this method is the most similar to the methods used to purify municipal water supplies.
Q2) Explain why desalination techniques, despite proven technological effectiveness, are not used more widely to produce potable drinking water.
Reverse osmosis and distillation are the 2 most common desalination techniques and energy is needed for both techniques to remove salts from seawater. The need for energy will be costly thereby making these techniques not widely used.
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?
The lead could come from the solder in pipe joints or the walls of the pipe itself.
b) Do the research activities carried out in this chemistry building account for the elevated lead levels found in the drinking water? Explain.
No if the lead is in experiments are disposed properly per protocol then it will not contaminate drinking water. Also toxic metal ions are not allowed in most basic experiments in a lab setting
4) Some vitamins are water-soluble, whereas other are fat-soluble. Would you expect either or both to be polar compounds? Explain.
I would expect water-soluble vitamins to be predominantly polar compounds whereas fat-soluble vitamins are predominantly non-polar compounds based on the concept of ‘like dissolves like’.
To put it in scientific terms, water-soluble vitamins are mostly polar because the energy released from the formation of polar interactions between water-soluble vitamins and water molecules are exothermic enough to overcome the comparably strong polar interactions between the vitamin molecules.
By the same logic, fat-soluble vitamins are mostly non-polar so that the energy released from the formation of non-polar interactions between fat-soluble vitamins and fats molecules are exothermic enough to overcome the equally weak non-polar interactions between the vitamin molecules.
Session 4: Unit 3 – Global Climate Change
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/m^2), but the energy leaving Earth’s surface averages 390 W/m^2. Why isn’t Earth cooling rapidly?
A: The Earth’s atmosphere retains a large percentage of heat. Thus, even though the amount of heat emitted by the Earth is more than double the amount of heat taken in, the Earth does not cool rapidly.
Q2. Decide and explain where the stamen is correct or incorrect. Explain.
A: The statement is incorrect. What the picture shows is actually the ignorance of the difference between climate and weather. This leads people to believe that global warming is not actually happening. In true fact, climate involves measuring the weather over a prolonged period of time, for example, 30 years. In contrast, weather involves measuring the atmospheric condition of a particular place over a short period of time. Thus, the changing of Seasons over the year does not indicate whether the Earth is cooling or warming. However, measuring the climate would help us with that.
Q3. One of the first radar devices developed during World War 2 uses microwave radiation of a specific wave range that triggers the rotation of water molecules. Why was the design not successful?
A: The design was not successful due to 3 main factors. Firstly, the devices’ microwave radiation heated up the air around the machine. Secondly, it resulted in operators of the radar getting contracting diseases. Thirdly, the radiation was absorbed by water molecules in the atmosphere, causing interference with the detection of the 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)?
A: In the short run, air quality will pose the most serious problem. This is due to the immediate observability and reaction to bad air quality. For example, haze could instantly trigger breathing problems. In comparison, ozone depletion and global warming do not have immediate observable effects and may take many years for the effects to seriously affects humans.
In the long run, global warming will pose the most serious problem. This is because the factors causing global warming can only be reduced but not completely removed. For example, the burning of fuel for energy can be reduced by replacing that with alternative sources of energy, such as solar energy. However, fuel consumption cannot be totally stopped. Hence, we can slow global warming but we might not be able to stop it completely, thus making it the biggest threat in the long run.
Session 3: Unit 4 – Energy from Combustion
Q1. From personal experience, state whether these processes are endothermic or exothermic. Give a reason for each.
A:
Q2. Chemical explosions are very exothermic reactions. Describe the relative bond strengths in the reactants and products that would make for a good explosion.
A: Explosions rely on the initial combustion or agitation of a substance to give off massive amounts of energy in a short period. This is because explosions reactions use substances that combust very quickly but also in such a manner that it will affect the substance next to it, thus creating a quick but violent chain reaction.
A chain reaction occurs when a substance with a weak chemical bond is agitated caused the bond to be broken. This broken bond releases large amounts of energy causing the substances next to it to break their bonds. This process will continue until all the substance is used up.
Q3. How might you explain the difference between temperature and heat to a friend? Use some practical, everyday examples.
A: Temperature is a measure of the average energy of molecular motion in a substance. For example, the average internal temperature of a human body is 37.0 degree Celcius. It uses arbitrary units like degree Celcius and Farenhit to give a gauge of the degree of hotness or coldness of an object.
On the other hand, heat is the total energy of molecular motion in a substance. For example, the heat of combustion of ethanol is 1360kJ mol-1. The term ‘heat’ is actually for layperson usage and should be replaced with ‘thermal energy’.
Q4. A premium gasoline available at most stations has an octane rating of 98. What does that tell you about:
a) the knocking characteristic of this gasoline?
A: An octane number of 98 means a knocking characteristic of 98% isooctane
and 2% heptane.
b) whether the fuel contains oxygenates?
A: The fuel may not contain oxygenates, i.e. methanol, ethanol, MTBE, and ETBE.