Exercise 8 – Molecules and Drugs
Question 1
In allergy sufferers, histamine causes runny nose, red eyes, and other symptoms.
a. Give the chemical formula for this compound
C5H9N3
c. Which part (or parts of the molecule make the compound water-soluble?
The nitrogen atoms attached to the hydrogen atoms is able to form a hydrogen bond with the water molecule.
Question 2
Antihistamines are widely used drugs for treating symptoms of allergies caused by reactions to histamine compounds. The class of drug competes with histamine, occupying receptor sites on cells normally occupied by histamine. Here is the structure for a particular antihistamine.
a. Give the chemical formula for this compound.
C16H21N3
b. What similarities do you see between this structure and that of histamine that would allow the antihistamine to compete with histamine?
One similarity is the two carbon chain with a nitrogen at the end (-C-C-N-). Another similarity is the -N-C-N- chain. It also has similar spatial placement. The flat 5-ring in histamine is also similar to the flat 6-ring in antihistamine.
With these similarities, antihistamine can then bind to histamine receptor sites on cells more tightly than histamine itself. This will block histamine action.
Question 3
“Drugs can be broadly classed into two groups: those that produce a physiological response in the body and those that inhibit the growth of substances that cause infections.” Into which class does each of these drugs fall into?
aspirin, antibiotics (Keflex), amphetamine, morphine, estrogen, pencillin
Produce a physiological response: aspirin, antibiotics, morphine
Inhibit the growth of substances: amphetamine, estrogen, penicillin
Question 4
Herbal or alternative medicines are not regulated in the same way as prescription or OTC medicines. In particular, the issues of concern are identification and quantification of the active ingredient, quality control in manufacture, and side effects when the herbal remedy is used in conjunction with another alternative or prescription medicine.
a) What do you think is the evidence from herbal supplement manufacturers that address these issues?
Herbal medicine may interact with prescription drugs
- May have opposite effect that prevents treatment from being effective
- May limit the absorption of a prescription drug in the body
b) Do you know anything about Singapore’s legislation on the topic?
Medicines Act classifies alternative medicines as complementary health products. Manufacturers are legally responsible for the safety of these products. They should not contain any substance under the schedule of the Poisons’ Act. In addition, labelling of such medicines must match the actual chemical composition of the physical product.
Exercise 7 – The World of Polymers and Plastics
Question 1
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.
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.
Question 2
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.
LDPE is too weak for this application.
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. A linear HDPE will possess characteristics like flexibility, and at the same time increases the strength.
Question 3
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. Why doesn’t the same thing happen to paper? Explain on a molecular level.
Plastic bags are most commonly made out of polyethylene. These branched polymers have low tensile strength and crystallinity, hence when stretched the polymers 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.
However, paper is most common made from cellulose, a naturally made homo-polysaccharide. Due to the extensive intra and intermolecular hydrogen bonds within the polymers, it has a high tensile strength and does not stretch easily.The cellulose molecules in paper are held far more rigidly in place, and are not free to become aligned. But this polymer is weak when a shearing force (i.e. tearing) is applied.
Question 4
A Teflon ear bone, fallopian tube, or heart valve? A Gore-Tex implant for the face or to repair a hermia? Some polymers are biocompatible and now used to replace or repair body parts.
a. List four properties that would be desirable for polymers used with the human body
(1) Stable over time of intended use
(2) Non-toxicity
(3) Ease of implantation
(4) Non-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 for 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.
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).
c. What is the difference in material used in “hard” and “soft” contact lenses? How do the differences in properties affect the ease of wearing of contact lenses?
Soft contact lens are mainly composed of soft, flexible plastics that are oxygen-permeable. These materials include silicone-hydrogels.
Hard contact lens are made of rigid plastics like poly-methyl-methacrylate (PMMA).
Soft contact lens are generally easier to wear. They are made of flexible plastics that stay in place and also more comfortable.
Hard contact lens get dislodged easily as they have higher rigidity and hence lower pliability.
Exercise 6 – Acid Rain
Question 1
Mammoth Cave National Parks 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?
b. The NPCA reported “the average rainfall in Mammoth Cave National Park is 10 times more acidic than natural.” From this information and that is in your text, estimate the pH of rainfall in the park.
a. Coal-fired plants emit particulate matter (PM2.5, PM10) tat becomes suspended in the air. These carbon-based soot particles reduce visibility by decreasing the permeability of light.
b. The estimate pH is 4.3. Knowing the natural pH of rainfall is about 5.3, a concentration of 10 times of [H+] ions, it will translate into a decrease of one unit on the pH logarithmic scale.
Question 2
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.
b. Walk, bike, or take public transportation 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
a. By hanging laundry to dry, it reduces the electrical energy usage to the dryer. Production of electricity requires burning of coal or natural gas, which produces harmful pollutants that are a major contributor of acid rain (SOx and NOx).
b. By reducing the energy usage of cars, we use less fuel. This reduces the emissions of NOx and SOx. This reduces the acid rain contribution.
c. Running dishwashers and washing machines on full load instead of small loads conserves water usage. Water is a key driver of chemical reactions that reacts with NOx and SOx to produce nitric acid and sulfuric acid respectively, which are the main contributors of acid rain.
d. Insulation reduces heat loss and increases water temperature, decrease the consumption of electricity. Power generation to drive the energy needed to supply electricity and heat comes mainly from fossil fuel combustion, which leads to the production of sulfur dioxides, that will react with water to form sulfuric acid – the cause of acid rain.
e. Trucks, planes, cars, trains, and boats that are powered by fossil fuels are a huge contributor to the sulfur dioxide and nitrogen oxides that cause acid deposition. By shopping locally at markets and stores that source their products nearby, transportation-related acid rain emissions being released into the atmosphere is reduced.
Question 3
a. Give names and chemical formulas for five acids and five bases.
b. Name three observable properties generally associated with acids and bases.
Acids
HCl (Hydrochloric Acid)
H2SO4 (Sulfuric Acid)
HNO3 (Nitric Acid)
H2CO3 (Carbonic Acid)
CH3COOH (Acetic Acid)
- Has a soapy feel
- Tastes sour (don’t taste please)
- Turns red litmus paper blue
- Corrosive
- Reacts with metals to form salt & water
Bases
NaOH (Sodium Hydroxide)
Ca(OH)2 (Calcium Hydroxide)
NH4OH (Ammonium Hydroxide)
Mg(OH)2 (Magnesium Hydroxide)
Ba(OH)2 (Barium Hydroxide)
- Tastes bitter
- Feels slippery
- Turns blue litmus red
Question 4
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 Singapore’s borders?
URL Provided:
http://www.ec.gc.ca/
http://www.ukawmn.ucl.ac.uk/
http://www.grida.no/
http://www.nea.com.sg/
Acid rain is driving Singapore’s remaining native species to almost extinction. This is due to the fact that water in stream on nature reserve have pH value of 4.4 to 4.7 making it more acidic thus animals are unable to cope with the changes in acidity.
Usually acid deposition originate outside of Singapore’s borders which can be seen in case where the Indonesian forest fire will release large amounts of gaseous and particulate pollutants into the atmosphere which will affect the air quality in Southeast Asia which will cause acid rain.
Exercise 5 – Water For Life
Question 1
How can you purify your water when you are hiking? Name 2 – 3 possibilities. Compare these methods in terms of costs and effectiveness. Are any of these methods similar to those used to purify municipal water supplies? Explain.
- Collect fine sand particles to create sand filtration mechanism using a plastic bottle. As sand is mainly made up of silicate, it can interact/remove the polar impurities of water.This is chemical purification as it removes polar chemical impurities.This is similar to industrial sand filter facilities used in municipal water treatment.
- Make a fire using dry twigs and a flint. Use the heat from the flames to kill bacteria in water by boiling it.This is biological purification as it removes microorganisms.
Question 2
Explain why desalination techniques, despite proven technological effectiveness are not used more widely to produce potable drinking water.
Costly
Chemicals produced in this process (e.g. Chlorine) may be dangerous to the environment
High land usage, damages ecosystem.
Question 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?
Pipes containing lead corrodes when water with high acidity or low mineral contain. This causes the lead to leak into the drinking water.
b. Do the research activities carried out in the chemistry building account for the elevated lead levels found in the drinking water? Explain.
Based on student accounts, all students conducting laboratory work in NTU are required to dispose of toxic/hazardous compounds in either a contained chamber. Furthermore, the pipes used in laboratory work are specially designed not to contain lead, but a less reactive material for highly reactive substances.
Question 4
Some vitamins are water-soluble, whereas others are fat-soluble. Would you expect either or both to be polar compounds? Explain
Water-soluble vitamins are expected to be polar compounds. They have hydrophilic compounds that allow them to form hydrogen bonds when dissolved in water.
Fat-soluble vitamins are vitamins that contain long chains of fatty acids, which are lipophilic and non-polar. These fatty acids are long hydrocarbon chains, hence they are non-polar.
Exercise 4 – Global Climate Change
Question 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 168 watts per square meter, but the energy leaving Earth’s surface average 390 watts per square meter. Why isn’t Earth cooling rapidly?
Energy leaving the surface of the Earth is still absorbed/reflected back to the Earth by the atmosphere. The presence of greenhouse gases absorb Infrared radiation from terrestrial surfaces, thereby preventing energy loss to outer space. Hence, the Earth isn’t cooling rapidly.
Question 2
“This winter has lowered my concerns about global warming. [Snow up to waist].” Decide and explain whether the statement is correct/incorrect.
The statement is incorrect as the increased melted ice observed during winter reflects the reality of global warming. The global temperature of the Earth is increasing.
Yet, winter is also attributed to seasonal changes and it’s occurrence is therefore not admissible as evidence that the Earth isn’t getting hotter.
Question 3
One of the first radar devices developed during WWII used microwave radiation of a specific wave range that triggers the rotation of water molecules. Why wasn’t the design not successful?
The atmosphere has water vapor present which intercepts microwaves that are propagated from the source. Hence, microwaves cannot be transmitted over long distances without diminishing in intensity. It is therefore not feasible to use radar devices that utilise microwaves.
Question 4
Which of the 3 units covered (1 – Air quality, 2 – Stratospheric ozone depletion, 3 – Global warming) poses the most serious problem to me (a) in the short run and (b) in the long run.
(a) Short run – Air quality
We breathe in air all the time. Therefore, if air quality is bad…we will die faster.
Millions of people die due to air pollution.
(b) Long run – Global warming
Global warming slowly results in climate change, resulting in sea levels rising, increase in global temperature. These conditions are gradual, and humans have adapted the ability to survive (air-con).
Exercise 3: Energy from Combustion
Question 1
Exothermic or Endothermic?
- A charcoal briquette burns – EXOTHERMIC, gives off heat
- Water evaporates from your skin – ENDOTHERMIC, cooling effect
- Ice melts – ENDOTHERMIC, requires higher temperature
Question 2
Chemical explosions are very exothermic reactions. Describe the relative bond strengths in the reactants and products that would make for a good explosion.
Weak bonds in reactants result in less energy intake required.
Strong bonds forming in products release a lot of energy.
This results in a huge difference between products and reactants energy content. Hence a significant release of energy in the form of an explosion.
Question 3
How might you explain the difference between temperature and heat to a friend? Use some practical, everyday examples.
Temperature is a measure of hotness, whereas heat is the flow of energy.
[From MA2003 (Intro to Thermo-Fluids)] Heat is a means of energy transfer between a system and its surroundings as a result of the temperature difference between them. Temperature difference is the driving force for heat transfer.
A boiling kettle is has a high temperature, therefore it is hot. You can feel the heat from the kettle due to the transfer of energy from the hot water to your hand. This transfer of energy is referred to as heat.
Question 4
A premium gasoline available at most stations has an octane rating of 98. What does that tell you about:
a. knocking characteristics of this gasoline?
b. whether the fuel contains oxygenates?
a. Rating of 98 has a knocking characteristic of 98% iso-octane and 2% n-heptane. It has higher octane rating than other blends sold at gasoline stations and hence is more resistant to knocking than these blends.
b. Yes. It tells us that the fuel contains oxygenates.