Question 1

a. C5H9N3

b.

c. Amine

Question 2

a. C17H21NO

b. 

The similarities are as below:

(a) a two-carbon chain with a nitrogen at the end (marked in red)

(b) a three-atom sequence of N-C-N (marked in blue).

(c) The flat 5-ring of histamine seems to be similar to the flat 6-ring of the antihistamine.

Due to the similarities in structure, the antihistamine will compete with histamine to bind to the histamine receptor sites on cells.

Question 3

Question 4

a.

The herbal supplement manufacturers are permitted to say, for example, that a particular herbal supplement addresses a nutrient deficiency, supports health, or is linked to a particular body function (like immunity or heart health). Such a claim must be followed by the words, “This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.” Besides, the herbal supplement manufacturers must follow certain good manufacturing practices to ensure the identity, purity, strength, and composition of their products. If a product is found to be unsafe or otherwise unfit for human consumption, the authorities may take enforcement action to remove the product from the marketplace or work with the manufacturer to voluntarily recall the product.

Reference: https://ods.od.nih.gov/HealthInformation/DS_WhatYouNeedToKnow.aspx

Products like herbs are sometimes tainted with germs, pesticides, or toxic heavy metals. Other supplements do not contain what’s listed on the label. Still, others contain more or less than the amount of the herb listed on the label. And many have ingredients that aren’t listed on the label at all.

This problem extends beyond the supplement makers and sellers. Some herbal suppliers (those who grow, harvest, or sell the crops) may mix or even substitute their crops with less expensive or more readily available plants. There’s also the problem of accidental contamination when one plant grows in with others, as well as cases of mistaken identity (when one plant looks like another). Given the global market, all of these problems can make it harder for a company to be sure that what they thought they were buying to make supplements is actually the herb they wanted.

b. There are limits for the safety and quality levels for heavy metals and microbial in the supplement.

“The product label should be prominently and conspicuously displayed on the product at the point of sale. Where the size, shape or nature of the final product or package does not permit the full listing of labelling information, the use of inserts, leaflets, hang tags, in appropriate format, will be allowed. However, the name of the product, the recommended dosage, the batch reference and relevant precautionary statements should be displayed on the final product or package.”

Reference: http://www.hsa.gov.sg/content/dam/HSA/HPRG/Complementary_Health_Products/Overview_Framework_Policies/Health_Supplements/HSGuidelines.pdf

Question 1:

Polymer is dissolved by the acetone, hence the gas of the foaming agent freely escapes. The polymer collapses on itself and is more dense because the gas has been expelled.

Question 2:

a. LDPE cannot be used in this application because the material is not strong enough.

b. The molecules of HDPE must line up according to the way that generates enough strength. Using linear HDPE is successful because it allows sufficient flexibility.

LDPE	HDPE

Question 3:

When the piece of plastic bag is stretched, the strip becomes narrow. The molecules are aligned parallel to each other according to the direction of the pull. This is a irreversible alteration of the three-dimensional structure, hence if the pulling persists, the plastic breaks. If this same pulling force is applied to a piece of paper, the paper will tear because it does not have stretching properties. The cellulose molecules in 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:

1. stable over time of intended use
2. non-toxic

Other factors to consider are:

1. low cost
2. lack of solubility in body fluids
3. lack of reactivity in body fluids
4. 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 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 (GRP) 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.

The desirable properties in these polymer materials are:

1. Unreactive to chemicals on the eye surface
2. Lets oxygen pass through the eye surface
3. Transparent and moderately flexible
4. Low density
5. Easy to manufacture from a raw material that is available in abundance

c. Difference in material used in “hard” and “soft” contact lenses

How it affects the ease of wearing of contact lenses:

a) What is the connection between coal-fired plants and poor visibility? 

Coal-fired plants produce sulfur dioxide, creating sulfate particles which is the culprit for 60-85% of poor visibility in the eastern parks.

b) The NPCA reported “the average rainfall in the 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.

The estimated pH of rainfall in the park is pH 4-5, because normal rain has a pH of 5-6. If rainfall in this park is 10 times more acidic, the range should be around pH 4-5.

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

Hanging laundry uses natural sunlight and wind to dry the clothes, whereas a clothes dryer requires electricity, which uses energy produced by power plants to dry the clothes. By avoiding the use of clothes dryer, we reduce the use of electricity and thus reduce the need to produce more energy through power plants (reduce burning of coals, reducing SO3 emissions).

b. walk, bike, or take public transportation to work

All of these options reduces acid rain production because they require less to zero amount of gasoline and has little to no emissions that contribute to acid rain production.

c. Avoid running dishwashers and washing machines with small loads.

Using larger loads reduce the energy per unit load in dishwashers and washing machines. This requires less energy to wash the same amount of items, so power companies don’t have to produce as much electricity by coal burning which emits SO3.

d. Add additional insulation on hot water heater and pipes

Additional insulation means less heat loss from the hot water heater and pipes, so the need to produce electricity to generate heat is lessened, reducing SO3 emissions.

e. Buy locally grown produce and locally produced food.

Buying locally grown produce and locally produced food reduce the use of gasoline which is needed in food transportation. This reduction in gasoline use results in less gas emissions that contribute to acidity of rain.

3.
a) Gives names and chemical formulas for five acids and five bases.

ACIDS: hydrochloric acid (HCl), nitric acid (HNO3), sulfuric acid (H2SO4), sulfurous acid(H2SO3) and phosphoric acid (H3PO4).

BASES: potassium hydroxide (KOH),  sodium hydroxide (NaOH), ammonium hydroxide (NH4OH), magnesium hydroxide (Mg(OH)2) and calcium hydroxide (Ca(OH)2).

b) Name three observable properties generally associated with acids and bases.

Generally, acids turns blue litmus paper red, corrodes metals, and release carbon dioxide from a carbonate. On the other hand, bases turn red litmus paper blue, have a soapy/slippery feel in water, and are caustic to skin.

4. The concerns of acid rain vary across the globe. Many countries in the 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 the Singapore’s borders?

From August to October 1993, the Indonesian forest fires that happened released large amounts of gaseous and particulate pollutants into the atmosphere. The emissions of particulates formed a plume that was visible by satellite and affected regional air quality in Southeast Asia significantly. This prolonged haze saga allowed us to examine the effects of biomass burning on regional atmospheric chemistry. A comprehensive study was done to assess the influence of biomass burning impacted air masses on precipitation chemistry in Singapore. 104 rain samples were collected and went through an automated wet-only sampler from July through December 1997, determining many major organic and inorganic ions. Mean pH values ranged from 3.79-6.20 with volume-weighted mean of 4.35. Many of the rain samples had elevated concentrations of these ions during the biomass burning period. The relatively high concentrations of sulfate, nitrate, and ammonium ions observed during the biomass burning period are due to the long residence time of air masses. This leads to gas progressively turning into particles of biomass burning emission components. The decrease in pH of precipitation in response to the increased concentrations of acids is only marginal. This is credited to the neutralization of acidity by ammonia and calcium carbonate.

One fine winter morning in Finland, John awoke to see clear blue skies with cotton clouds outside his window. He decided to venture out into the woods and hike up the mountain just a few kilometres away from his countryside house. He assembled his hiking gear, grabbed his winter jacket, and promptly began his journey.

The feeling of having forgotten something lingered in John’s minds from the time he locked his house doors. He could not pinpoint what he had seemingly forgotten. Nevertheless, he trudged on. In the forest, his feet crunched away at the snow and gravel on the deserted bike trail when a sudden gust of wind blew, rustling the snow-laden branches overhead and the some of the snow fell. He felt lucky as his winter jacket had a hoodie that prevented the snow from landing on him and melting because of body heat. He could get cold if he was wet. It was then he realised that he had forgotten his water bottle.

John did not want to make a detour home for water as it would waste precious daylight. He recalled what his high school teacher taught them about purifying water for drinking. There were several methods, he recalled, and the danger of drinking non-purified water is that bacteria and harmful organisms like salmonella could be present [1].

He found a river hidden in the forest, where most of the water had froze over, leaving a small trickle that came from the mountains. He stopped in his tracks and decided to try the first method of purifying water for drinking. The first method of purifying water is by boiling. In science class, John was taught that the boiling point of water decreases as atmospheric temperature decreases.  . Thankfully he was still at an approximate altitude near sea-level (1 atm of pressure). He took out a matchbox and started a small fire. John knew that the number of microorganisms can be reduced to non-detectable levels, simply by raising the temperature of water to roughly 65 ºC [3]. In addition, he could build a bigger fire in an attempt to raise the temperature to 100ºC (at 1 atm) where boiling occurs. At 100ºC, most bacteria and microorganisms will be killed. However, John was wary that water could still be contaminated with chemicals.

John’s memory was jolted when he recalled watching a documentary about filtration devices. He was certain that by using a filtration device, water could be easily purified and drinkable, and does not need removing his gloves to light a match in the cold. To his dismay, he did not have any with him.

He had an idea of using finely packed sand to filter water. He looked around, and realised that all that surrounded him were sheets of white snow. The sand was buried beneath 1 feet of snow. Well, he could dig for the sand, but it would render him more thirsty in the end. Nope, he ruled it out.

John sat by the river bank, pondering if there were any other methods of water purification. He ruled out distillation, as it was a time consuming method given that he only had a few matchsticks remaining. He thought of chemical methods, such as using chlorine or iodine, but there was a smell which he did not like [4, 5]. Nope, he ruled it out as well.

At last, a decision was made to head back home where it had safe drinking water. It was unfortunate that John had to cut his hike short, but he trusted in the municipal water system to provide clean and drinkable water. John was confident of the town’s method of water purification through the concurrent use of coagulation and flocculation, sedimentation, filtration, and disinfection [6].

References:

[1] Caterina Levantesia et al. Salmonella in surface and drinking water: Occurrence and water-mediated transmission.
[2] The Engineering Toolbox. Boiling Point of Water and Altitude. Retrieved from http://www.engineeringtoolbox.com/boiling-points-water-altitude-d_1344.html.
[3] Robert Angelotti et al. Time-Temperature Effects on Salmonellae and Staphylococci in Foods
II. Thermal Death Time Studies.
[4] Drinking Water and Chlorine Odor, http://www.waterandhealth.org/drinking-water-chlorine-odor/
[5] How To Purify Water With Iodine For Survival, http://www.survivopedia.com/how-to-purify-water-with-iodine/
[6] Community water treatment, https://www.cdc.gov/healthywater/drinking/public/water_treatment.html.

Question 2:

Water can be purified to drinking standards through the use of desalination. There are two main methods, distillation and reverse osmosis.

Distillation is a process in which heat is supplied to non-purified water in order to evaporate the water. Once evaporated, the water vapour is cooled in the condenser, and will condensed water will be collected in a flask as seen in the figure above.

One drawback of distillation is that it requires energy to heat water to its boiling point. The specific heat capacity and latent heat of water does not change, hence despite technological advances, the amount of energy needed to evaporate the water is the same. Energy is also required for the pumping of water through the condenser.

Osmosis is a natural process in which water is passed through a concentration gradient (from high concentration of water to low concentration of water) through a partially permeable membrane. Osmosis will take place even in the absence of supplied energy, so long as the concentration gradient is present.

Reverse osmosis is not a natural process in that it requires energy to pump water through the membrane. The figure above highlights that pressure (energy to supply this pressure) is applied on water with high salt concentration through the partially permeable membrane.

The downside of reverse osmosis compared to distillation is that there could still be dissolved chemicals lingering after passing through the membrane. Reverse osmosis also requires the frequent replacing of membranes to ensure that it functions properly [1].

In general, distillation and reverse osmosis are desalination techniques that require huge amounts of energy and costs for purification.

References:

[1] M. Shanker et al. Is Reverse Osmosis Effective for Produced Water Purification? Viability and Economic Analysis, SPE 115952.

Question 3:

Water which has high acidity or low mineral content causes pipes and solder joints to corrode, enabling the lead to be present in drinking water [1].

In a chemical engineering department, it is inevitable that lead is used in experiments. There are two possible outcomes. Lead that is disposed into the drainage system will get into the sewage system which will account for elevated lead levels. Lead that is properly disposed of will not account for these elevated lead levels.

References:

[1] How Lead Gets into Drinking Water. https://www.epa.gov/ground-water-and-drinking-water/basic-information-about-lead-drinking-water#getinto

Question 4:

Vitamins B and C are water soluble, while vitamins A, D, E, and K are fat soluble.

The main difference between water solubility and fat solubility stems from the polarity of molecules [1].

When polarity is mentioned, it does not have anything to do with polar bears. A polar molecule means that it has an overall non-zero dipole moment, where there is a separation of charge, inducing electronegativity in the molecule [2].

Water soluble vitamins are overall polar. These vitamins contain polar groups that outweigh the non-polar groups. This non-zero polarity will cause these molecules to mix with water molecules as water molecules themselves are polar.

Fat soluble vitamins are overall non-polar. These molecules may contain polar groups, but are outweighed by non-polar groups, enabling them to mix with non-polar lipids, which render them fat soluble.

References:

[1] Are Vitamins Non-polar? http://allvitahealth.blogspot.sg/2015/08/are-vitamins-non-polar.html
[2] Dipole Moments, https://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Physical_Properties_of_Matter/Atomic_and_Molecular_Properties/Dipole_Moments

Although the amount of energy that leaves the earth’s surface is more than half of the amount of energy that reaches the surface, the earth does not cool rapidly due to the presence of greenhouse gases in the atmosphere. Greenhouse gases like CO2, water vapour, methane and many others have the ability to retain heat from the emitted heat energy, keeping the earth warm.

Question 2

This quote is incorrect and probably used to mock at people who does not know the difference between weather, climate and global warming. This is because a cool season like winter does not signify that the earth is cooling down instead of getting warmer and warmer due to global warming. To study the rate of global warming, scientist studies the average weather over a period of time known as the climate. In addition, another sign of global warming can also be extreme weather conditions like longer winter that usual as illustrated in the source which shows overflowing snow as a sign of long winters.

Question 3

It wasn’t successful because the machine causes the surrounding air to be heated up as well. Since radiation was used, it caused diseases to the machine operators. In addition, the water molecules present in the surrounding air also absorbed the radiation from the machine and gives interfering results, leading to inaccurate data obtained. As such, the machine was not a successful design.

Question 4

We believe that air quality poses the most serious effect for us in the short run whereas in the long run, global warming is the most serious effect.

Air quality poses the most serious effect in short run is because we are living in a bustling city where there are more architectures than trees around us and we live an active lifestyle whereby we have to be outdoors almost everyday. Hence, if the air quality is bad, our health will be affected almost immediately.

However, global warming on the other hand is a long run issue as global warming causes a change in the climate/weather which is changing at a much slower state for now. however, in long run, the small change in weather/climate now(which most have not realised yet) will slowly adds up and become a significant change in the future.

QUESTION 1

a. A charcoal briquette burns

> Exothermic as heat will be released by the burning charcoal briquette.

b. Water evaporates from your skin

> Endothermic as heat will be absorbed during evaporation.

c. Ice melts

> Endothermic as heat will be absorbed during melting.

QUESTION 2

Bond breaking in reactants will be an endothermic process whereas bond formation in products will be an exothermic process.

The energy absorbed during bond breaking (reactant) must be low while the energy released during bond formation (product) must be high to result in a negative net energy change, which also refers to an exothermic reaction.

For a good explosion, bond strength of reactants should be weak so lesser energy will be required to break bonds while bond strength of products should be strong so as to release more energy. This will result in a greater negative net energy change and hence a very exothermic reaction (good explosion).

QUESTION 3

Temperature is a form of measurement whereas heat is a form of energy.

For eg, comparing between a drop of hot water and a cup of hot water. Both are of the same temperature but it will be more tolerable to touch a drop of hot water as compared to a cup of hot water due to the difference in heat content.

QUESTION 4

a. Gasoline with an octane rating of 98 has the same knocking characteristic of 98% isooctane and 2% heptane. It has high octane rating hence it will be resistant to knocking.

b. The octane number of the gasoline will not tell us if it contains oxygenates but fuel with oxygenates do have higher octane ratings. Some common oxygenated fuel additives have octane ratings of over 100.

Soot and ash are particulate matter that can contribute to air pollution.

Came into class today and realised that there is an individual test !?!?!

Today I made new friends! 😄 Matthew from Physics, XC and Ying Jie from Chemistry, Yingshi from Bio and Yayu from ADM 😜

And… I learnt that the primary component of an exhaled breath is Nitrogen. Not CO2. Whoa.

Testing Testing Testing

We are learning how to post this post on the blog.

We just learnt how to create tags. This goes to the tag cloud.