Week 11 – Application Exercise Answers

Question 1

(a) C5H9N3


(c)  The amine groups, as hydrogen bonds can form between the lone pair on the very electronegative nitrogen atom and the slightly positive hydrogen atom in a water molecule.

Question 2

(a) C16H21N3

(b)  Both have an ethylamine group (-CH2-CH2-N-)

Question 3

Those that produce a physiological response in the body:





Those that inhibit the growth of substances that cause infections:

-Antibiotic (Keflex)


Question 4

(a)  Because of the inherent complexity of naturally grown medicinal plants and the often variable nature of cultivated ones, the examples of contamination with toxic medicinal plants and/or plant parts and the number and small quantity of defined active ingredients, the production, and primary processing has a direct influence on the quality of herbal medicines. For this reason, application of good manufacturing practices in the manufacture of herbal medicines is an essential tool to assure their quality.

As a result, most manufacturers of herbal medicines have now incorporated necessary details in the product design, such as the list of ingredients, the recommended dosage, warnings (eg. not suitable for pregnant women or those taking certain Western medicine concurrently), as well as the place of manufacture. Product labels are almost always conspicuously displayed and elaborate leaflets are also almost always included in the product.

In Singapore, manufactured alternative products are subjected to screening by respective authorities for safety and control before being marketed.

(b)  According to HSA, these Acts cover health supplements:

A. Medicines Act (Chapter 176) & its Subsidiary Legislation especially:
i. Medicines (Prohibition of Sale & Supply) Order;
ii. Medicines (Traditional Medicines, Homoeopathic Medicines and Other
Substances) (Exemption) Order;
iii. Medicines (Non-Medicinal Products)(Consolidation) Order;
iv. Medicines (Labelling) Regulations;
v. Medicines (Medical Advertisements) Regulations;
vi. Medicines (Licensing, Standard Provisions & Fees) Regulations

B. Medicines (Advertisement & Sale) Act (Chapter 177)

C. Sale of Drugs Act (Chapter 282) & its Regulations especially:
i. Sale of Drugs (Prohibited Substances) Regulations;
ii. Sale of Drugs (Prohibited Drugs) (Consolidation) Regulations;
iii. Sale of Drugs (Rhodamine B) Regulations 1993

D. The Poisons Act (Chapter 234) & The Poisons Rules


Health Supplements Guidelines (PDF). (2015). http://www.hsa.gov.sg/content/dam/hsa/hprg/complementary_health_products/overview_framework_policies/health_supplements/hsguidelines.pdf


Week 10 – Application Exercise Answers

Question 1

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

Question 2

(a) LDPE cannot be used in this application because it does not have the required strength.

(b) The molecules of HDPE must be arranged in a way that produces the required strength. Using a thin layer of HDPE allows sufficient flexibility.

Question 3

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 irreversible. If the pulling continues, the plastic breaks. When the same pulling force is applied to a piece of paper, the paper tears rather than stretch to any significant extent. The cellulose molecules in the paper are held far more rigidly in place and are not free to become aligned.

Question 4

(a) The benefits for polymers intended for use in the body should far outweigh any risks. The two main properties are (i) stable over time of intended use and (ii) non-toxic. Other factors to consider are low cost, lack of solubility in body fluids, lack of reactivity in body fluids, and the ease of implantation.

(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 non-gas permeable lenses, is structurally similar to Lucite and Plexiglas. Silicone-acrylate materials are now more commonly used under trade names such as Kolfocon. Newer rigid gas permeable (RGP) polymers contain fluorine: fluro-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 non-toxic, permeable to oxygen, comfortable to wear, and inexpensive. Additionally, it is preferred if it has the ability to conform to the shape of the eye and easily cleaned (if it is not disposable).

(c) As mentioned in the previous part, 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.

Week 9 – Application Exercise Answers

Question 1

(a) The burning of coal (1-6% sulfur) produces varying amounts of SO2. Once SO2 is in the air,  it reacts with oxygen molecules in the atmosphere to form SO3, which acts as a formation of aerosols.

S (s) + O(g) → SO(g) [Burning]

2 SO(g) + O(g) → 2 SO(g) [Reaction with Air]

Aerosols do not absorb sunlight but instead reflects it, thereby reducing visibility.

Moreover, combustion from coal plants also releases huge amounts of water vapor.

CH(g) + O(g) → CO(g) + 2 H2O (g)

Water vapor when cooled in the hilly forest becomes visible as fog.

(b) Natural rain is slightly acidic due to atmospheric carbon dioxide dissolving in and reacting with water to produce weak carbonic acid. Hence the approximated pH for natural rain is around pH 5.3.

Given that the pH scale is a log scale, if the acid level is 10 times stronger, it is equivalent to 1 pH more acidic. Hence, the NPCA reporting that the rain in Mammoth Cave National Park is 10 times more acidic than natural would mean that the rainfall in the park is approximately pH 4.3.

Question 2

(a) Instead of using a dryer, hang your laundry to dry it. A large portion of acid rain emissions can be attributed to power (that comes from gas or coal) generated by appliances. The idea is to use less power (reduce SO2 emission).

(b) Automobile transportation emits high levels of NOx, which contributes to the extra acidity in rain. Walk, bike, or take public transportation to work helps reduce NOx emission rate (less cars).

(c) Avoid running dishwashers and washing machines with small loads helps to reduce energy and power consumption (reduce SO2 emission).

(d) Adding additional insulation on hot water heaters and pipes helps to reduce energy use by preventing heat and cold from escaping (reduce SO2 emission).

(e) Non-locally produced food requires transportation (e.g. trucks, planes, cars, trains, boats) that are powered by fossil fuels. By purchasing locally produced and grown foods, it helps to reduce transportation-related emissions (NOx) being released to the atmosphere.

Question 3

(a) Names and chemical formulas for 5 Acids:

  1. Sulfurous acid (H2SO3)
  2. Sulfuric acid (H2SO4)
  3. Nitric acid (HNO3)
  4. Hydrochloric acid (HCl)
  5. Carbonic acid (H2CO3)

       Names and chemical formulas for 5 Bases:

  1. Sodium hydroxide (NaOH)
  2. Magnesium hydroxide (Mg(OH)2)
  3. Ammonia (NH3)
  4. Barium hydroxide (Ba(OH)2)
  5. Potassium hydroxide (KOH)

(b) 3 observable properties for Acids:

  1. Sour taste
  2. Turn blue litmus paper red
  3. pH less than 7

       3 observable properties for Bases:

  1. Bitter taste
  2. Turn red litmus paper blue
  3. pH greater than 7

Question 4

The main concern of acid rain in Singapore is the fear of wiping out native species. A study showed that 20 species of animals plentiful in the Singapore’s Bukit Timah Reserve in the 1980s, including frogs, crabs and fish are slowly being wiped out [1]. Researchers have found that the water in the stream on the nature reserves to have a pH value of 4.4 to 4.7, which is believed to be more acidic now than 20 years ago [1]. Singapore is therefore, dealing with acid rain (e.g. National Environment Agency monitoring rainfall acidity) in an aim to preserve the native species and wildlife reserves in Singapore.

Acid deposition can originate both outside and inside of the Singapore’s border. An example of acid deposition from outside is the Haze (which originates from the deforestation of Singapore’s neighboring country, Indonesia) An example of acid deposition from inside is attributed to Singapore being a tropical stream, which are naturally acidic.

[1] http://wildsingaporenews.blogspot.sg/2009/09/native-species-in-singapore-may-be.html#.WMlB3G-GOM8 

Week 7 – Application Exercise Answers

Question 1

water-tank-disinfection-tablets-aquatabs-rawalpindi-201509160555182271580000                    bulk-buy-aquatabs-water-purification-tablets-2487-p

Purification Tablets – Cheap, requires about half an hour to purify. To be used on water without sediments.

lifestraw-in-use-cropped                            18s0xpp96523djpg

Filtration Straws – Cheap, instantaneous usage. But has to be replaced after a certain amount of uses.

Boiling of Water – Requires fuel, takes about 15mins to boil. Has to be filtered before the start of boiling to reduce the amount of sediments.

Purification methods of municipal water supplies consist of:

Filtration Systems, similar to Filtration Straws
A water filter is a device which removes impurities from water by means of a physical barrier, chemical, and/or biological process.

Distillation Systems, similar to Boiling which involves heat
Distillation is a process in which impure water is boiled and the steam is collected and condensed in a separate container, leaving many of the solid contaminants behind.

Disinfection, similar to Purification Tablets, Boiling
Disinfection is a physical or chemical process in which pathogenic microorganisms are deactivated or killed. Examples of chemical disinfectants are chlorine, chlorine dioxide, and ozone. Examples of physical disinfectants include ultraviolet light, electronic radiation, and heat.

Question 2


Desalination of water requires a lot of energy. Salts dissolves very easily in water, forming strong chemical bonds, and those bonds are difficult to break. Energy and the technology to desalinate water are both expensive, and this means that desalinating water can be pretty costly.  Also, the residue is very saline brine, which must be disposed of without causing too many environmental problems.

Question 3


The corrosion from the piping used to transport water.

(b) No, the research activities carried out in the chemistry building do not account for the elevated lead levels found in the drinking water. The drinking water pipeline and the pipeline used for research purpose are totally different pipelines. They are not interlinked, so water used in the research activities will not contaminate the drinking water.

Question 4

Colorful pills on spoon

Water soluble vitamins are polar. They contain polar groups such as -OH which can interact with other polar water molecules, via hydrogen bonding. Fat soluble vitamins are non-polar. They have few or no polar group, thus they tend to interact with the hydrophobic fatty acid tail found in lipids.

Week 6 – Application Exercise Answers

Question 1

Even though the amount of energy emitted from the surface is more than double the amount received from the sun, Earth does not cool rapidly. The surface of Earth absorbs a large amount of energy from the atmosphere. The presence of greenhouse gas will also trap radiation within the atmosphere, resulting in higher temperatures in the atmosphere. Hence, inhibiting the rapid cooling of the Earth.

Question 2

The statement is incorrect. The sea levels are still rising even in the polar climates, for example, in the Northern and Southern Hemisphere.
The observation is too narrow to explain the global phenomenon. While the said cartoon could apply to that specific region/zone, the effects of global warming is still omnipresent and continues to affect the other parts of the world.
As illustrated in the cartoon, the water levels are still rising, yet Pepper and Salt are oblivious and choose to ignore the warning signs of global warming.

Question 3

The use of microwave radar devices during WWII was not a feasible idea. Water in the atmosphere would absorb the microwave radiation which triggers the rotation of the molecules, thus reducing the efficiency of the microwave radars as energy is not fully transmitted.

Question 4

In the short run, air quality (Unit 1) poses the most serious problem in the short run. It creates the most immediate effect compared to the other two units. This is because when the air quality is compromised, mankind has to wear masks to reduce the inhalation of particulate matter, which could induce immediate effects on oneself, such as breathing difficulties, shortness of breath, etc.
In the long run, global warming (Unit 3) has the greatest impact on the world. Effects include melting ice caps resulting in higher sea levels, which causes the loss of habitat for animals such as polar bears. There will be increase in average global temperature, which could indirectly implicate mankind by loss of homes due to flooding. Low lying land areas will be submerged.

Week 5 – Application Exercise Answers

Question 1

  1. Exothermic. It is a combustion reaction.
  2. Endothermic. Liquid water molecules absorb energy to overcome the intermolecular forces between h20 molecules to become gaseous vapour.
  3. Endothermic. When solid ice melts into water, energy is absorbed, increasing kinetic energy of its molecules, explaining its liquid state.

Question 2

To make a good explosion, the total amount of energy in reactants should be much, much greater than the final total amount of energy in its products, so that the enthalpy change (-ΔH/ energy released) will be huge.

Therefore, bond strength in reactants has to be very strong as compared to bond strength in products (weak).

Question 3

Temperature is an objective measurement of the amount of heat energy present in a body, which is represented using units like the Kelvin scale (for absolute temperature) and Celcius/Fahrenheit.

eg. “It is hot and sunny outside. The weather forecast says it would be 37 degrees Celcius.”

Heat refers to the total energy of all molecular motion inside an object. The hotter an object, the more rapid the molecules move inside it. Heat is also defined as the transfer of kinetic energy from one body to another.

eg. “Put the pack of ice next to the frozen food we bought, not next to the hot food, or else the ice will melt faster from the heat.”

eg. Heating a beaker of water over a bunsen burner with a thermometer.

eg. Chemical energy from burning of gas is converted to thermal energy to heat the water, which results in the bubbling of water and a rise in surrounding air temperature. The amount of heat energy converted is measured by the thermometer in the water.

Heat can be physically felt, temperature cannot. Heat energy depends on the size and type of object on how it conducts heat; temperature not dependent.

eg. A metal plate and a book in the same set-up, both are at same temperatures, however the heat we perceive when we touch them are different.

Question 4

(a) Octane rating of 98: knocking characteristic of 98% isooctane & 2% heptane. The higher the octane number, the more compression the fuel can withstand before igniting. It is a measure of the ability of gasoline to burn smoothly without knocking (resistance).

(b) Octane rating provides no information about the presence of oxygenates.

CM8001 Group 18

Skip to toolbar