Application Exercise 9: Molecules and Drugs

In allergy suffers, histamine causes runny nose, red eyes, and other symptoms. Here is its structural formula. 

Give the chemical formula for this compound.
1a. C5H9N3



Circle the amine functional groups in histamine.

Which part (or parts) of the molecule make the compound water soluble?
1c. Nitrogen groups, amine groups = They are able to form hydrogen bonds, making the compound soluble in water. 

Give the chemical formula for this compound.

What similarities do you see between this structure and that of histamine (shown in the previous question 1) that would allow the antihistamine to compete with histamine?
2b. They all have amine groups which are responsible for the binding between the compound to the receptor. Thus Anti-histamine is capable of competing with histamine for binding to the histamine receptors to inhibit the onset of allergic reactions

3. Consider this statement. “Drugs can be broadly classed into two groups: those that produce a physiological response in the body and those that inhibit the growth of substance that cause infections.” Into which class does each of these drugs fall?

Inhibit growth of substances that cause infection
Keflex antibiotic

Produce physiological response in the body

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 prescription medicine.

What do you think is the evidence from herbal supplement manufacturers that address the issues?
4a.But since they became widely available in 1994, the FDA and some independent researchers have found problems with some dietary supplements. 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.

In 2013 researchers in Toronto published a report in which they sampled and analyzed 44 herbal supplements. The supplements were sold in both the US and Canada, and labeled as containing single herbs. Using DNA bar coding analysis, less than half the supplements (48%) contained any of the herb listed on the label. More than half of the supplements contained something that wasn’t on the label (substitutions or fillers). Even among the samples that contained the herb on the label, many also contained fillers or contaminants.

Do you know anything about Singapore’s legislation on the topic? 
4b. No, however upon research, my group managed to find information and understand how legislation on this topic works in Singapore. The enactment of the Act that all forms of TCM practice would be regulated. The Act, by virtue of section 14(1), states that the Minister for Health may, by order published in the Gazette, declare any type of practice of traditional Chinese medicine as a prescribed practice for the purposes of the Act if he is of the opinion that it is in the public interest for that type of practice to be regulated. The Ministry of Health’s intention is to start with acupuncturists, because it is an invasive procedure that carries risks of injury and infection. Accordingly, by way of the Traditional Chinese Medicine Practitioners (Prescribed Practice Of Traditional Chinese Medicine) Order 2001, the Minister for Health declared, pursuant to this section, that acupuncture is a prescribed practice of TCM. As part of the regulation of acupuncturists, the Minister for Health also made the Traditional Chinese Medicine Practitioners (Registration of Acupuncturists) Regulations 2001 (the ‘Regulations’) which came into effect on 23 February 2001. The Regulations prescribe the procedure and requirements for being registered as an acupuncturist. Broadly speaking, in order to be registered, a person must have the required qualifications and experience. In addition, the person seeking registration may also be required to take and pass a qualifying examination. This will be the case where he does not have the requisite experience or his qualifications are not of a specified kind. It should be noted that sections 24 and 25 of the Act have not yet come into force. These sections deal with the unlawful engagement in prescribed TCM practices (namely, acupuncture). As these are not currently in force, acupuncturists have effectively been given a grace period to ready themselves for the need to register with the Board.

Application Exercise 7: The World of Polymers & Plastics

  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.Hint:Remember that Styrofoam is made with foaming agents.
    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.
  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 cannot 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.

    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?
    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

  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. Does the same thing happen when you pull on a piece of paper? Why or why not? Explain on a molecular level.

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

  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.
    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 and (2) 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. 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.
    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).

Why is it important? – Biofuel

Biofuel vs Fossil Fuel

Fossil fuels are more expensive as pumping fuel from the ground is a difficult and expensive process, fossil fuels are also limited by availability as it requires millions of years to produce. Thus the availability of fossil fuels cannot keep up with the demand for energy making it more expensive.
Available land area
Due to limited land area it is impossible to grow enough biomass to make biofuels as there is only a limited area of land which can be used for farming etc. The land is also required for growing food not just biomass for biofuels thus it makes it very hard to meet both demands
Biofuels contribute to Global warming 
The energy required to convert biomass to biofuel is more than the energy produced by these biofuels.
At the same time fertilizers are used for the growth of these crops and they contain nitrous oxide that causes global warming

Application Exercise 6: Neutralising the Threat of Acid Rain

  1. 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?
    Sulfur dioxide are release from the coal-fired plants, creating sulfate particles responsible for 60% to 80% of the poor visibility in eastern parks. 

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.
Normal rain has a pH range of 5–6, so if the rainfall in this park is 10 times more acidic,the pH range must be 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 to dry requires less energy as compared to using a clothes dryer. An electric dryer required power that are produced by companies through the burning of coal. 

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

By walking or taking a bike, we are not burning any energy sources such as coal and gasoline that will contribute to acid rain. Public transportation is better than driving individually as it reduces the amount of gasoline used hence reducing emission. Therefore, contributing less to the acidity of rain.

c. Avoid running dishwashers and washing machines with small loads.
Maximum energy efficiency. Dishwashers and washing machines are powered by companies by burning coal which contribute to the increase acidity of rain.

d. Add additional insulation on hot water heaters and pipes.
Insulating hot water heaters and pipes can reduce heat loss and raise water temperature. Therefore, less coal is needed to be burn to power the above appliances, hence reducing acid rain. 

e. Buy locally grown produce and locally produced food.


Food miles refer to distance a food item had travel from farm to household. Therefore, to conserve energy and reduce global climate change, we should buy more locally grown and produced food. A tremendous amount of fuel are used to transport food long distances. The combustion of fuels will release carbon dioxide, sulfur dioxide, particulate matter and other pollutants into atmosphere, contributing to climate change, acid rain and air pollution. Refrigeration are also required to keep products fresh resulting in more coal used to power it.

3a. Give names and chemical formula for five acid and five bases.
– Hydrochloric acid: HCI

– Carbonic acid: H2CO3
– Nitric acid: HNO3
– Sulfuric acid: H2SO4
– Sulfurous acid: H2SO3

– Sodium hydroxide: NaOH

– Potassium hydroxide: KOH
– Calcium hydroxide: Ca(OH)2
– Ammonium hydroxide: NH4OH
– Methyl amine: CH3NH2

3b. Name three observable properties generally associated with acids and bases.
– The word acid derived from Latin word acere, France word acide & Germany word säure which

means sour. All acids taste sour such as vinegar and lemon juice.
– Acids make litmus (a blue vegetable dye) turn red.
– Acids destroy chemical properties of bases.

– All bases taste bitter. Mustard and most medicines are bases.
– Bases will restore the original blue colour of litmus after reddened by an acid.
– Bases destroy chemical properties of acids.

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 the Singapore’s borders?

According to Environment and Climate Change Canada (, acid deposition is a general term that includes more than simply acid rain. Acid deposition is primarily the result of emissions of sulphur dioxide (SO2) and nitrogen oxides (NOx) that can be transformed into dry or moist secondary pollutants such as sulphuric acid (H2SO4), ammonium nitrate (NH4NO3) and nitric acid (HNO3) as they are transported in the atmosphere over distances of hundreds to thousands of kilometres.

Acidic particles and vapours are deposited in two processes – wet and dry deposition. Wet deposition is acid rain, the process by which acids with a pH normally below 5.6 are removed from the atmosphere in rain, snow, sleet or hail. Dry deposition takes place when particles such as fly ash, sulphates, nitrates, and gases (such as SO2 and NOx), are deposited on, or absorbed onto, surfaces. The gases can then be converted into acids when they contact water.

A research was conducted by Balasubramanian, R.; Victor, T.; Begum, R., Tittle: Impact of biomass burning on rainwater acidity and composition in Singapore, in 1999.

The research look into the impact of the Indonesian forest fires that took place from August through October 1997. Large amounts of gaseous and particulate pollutants were released into the atmosphere. The particulate emissions produced a plume that was easily visible by satellite and significantly affected regional air quality in Southeast Asia. The prolonged haze episode provided an unprecedented opportunity to examine the effects of biomass burning on regional atmospheric chemistry. The researchers undertook a comprehensive field study to assess the influence of biomass burning impacted air masses on precipitation chemistry in Singapore. Major inorganic and organic ions were determined in 104 rain samples collected using an automated wet-only sampler from July through December 1997. Mean pH values ranged from 3.79 to 6.20 with a volume-weighted mean of 4.35. There was a substantially large number of rain events with elevated concentrations of these ions during the biomass burning period. The relatively high concentrations of SO4 2-, NO3 -, and NH4 + observed during the burning period are attributed to a long residence time of air masses, leading to progressive gas to particle conversion of biomass burning emission components. The decrease in pH of precipitation in response to the increased concentrations of acids is only marginal, which is ascribed to neutralization of acidity by NH3 and CaCO3.



Carbon Fixation
The process of taking an inorganic compound e.g. Carbon Dioxide to organic compounds. If it happens in a living organism its called biological carbon fixaton.

A hydrocarbon by or from a living organism that humans can use to power something e.g. cars or any hydrocarbon produced by or from a living organism in a short period of time.

Organic matter, dead material that was once living e.g. kernel of corn sugar cane etc. It is used to make biofuels and this makes biofuel more renewable as biomass can be reproduced in a short time.

Examples of biofuel vs its fossil fuel counterparts

Biofuel Fossil Fuel Differences
Ethanol Ethane/ Gasoline Ethanol burns cleaner than gasoline but it only has half the energy per unit mass of gasoline. Thus it produces less carbon monoxide but more ozone which contributes substantially to smog
Biodiesel Diesel Burns cleaner than diesel, produce less particulate and fewer sulfur compounds. However, it is corrosive to the engine thus modifications have to be done for the engine to take biodiesel. Has only slightly less energy per unit mass than diesel
Methanol Methane Easier to transport as compared to methane as it’s in the liquid form. Only has one third to half as much energy per unit mass as methane.
Biobutanol Butane/ Gasoline Can run in any car that uses gasoline, contains almost the same energy per unit mass as gasoline


Alcohols contain very little or no sulfur thus combustion of alcohol produces very little sulfur dioxide and sulfuric acid. However, alcohols are derived from plant and animal matter thus containing a lot of nitrogen. This is bad as it will produce a lot of nitric oxides and other nitrogenous compounds which contributes to acid rain in the long run

However, burning alcohols and biodiesel produces less carbon monoxide as compared to petrol diesel.

Production of biofuels from biomass
Biofuel: Ethanol

Biomass: sugar cane, corn, wheat, sugar beets, industrial sweet potatoes

Method of production: Biochemical Conversion

Enzymes and microorganisms Catalyse the conversion of biomass or biomass-derived compounds into desirable products. Enzymes such as Cellulase break down the carbohydrate fractions of biomass to five- and six-carbon sugars via hydrolysis, Yeast and bacteria then ferment the sugars into products


Application Exercise 5: Water for life

  1. How can you purify your water when you are hiking? Name two or three possibilities. What are the relative costs and effectiveness of these alternatives? Are any of the methods similar to those used to purify municipal water supplies? Explain.

    Several options exist for purifying water while hiking. The traditional method is to boil it. Boiling kills many microorganisms that may make you sick, but requires time and will not remove chemical contamination. Boiling also requires time, fuel, and may release soot and CO to the environment.

    Another method of water purification is with iodine. It is easy and effective in twenty minutes, but iodine should not be used long-term., In addition, pregnant women and people with thyroid conditions should avoid purification with iodine. While iodine renders water bacteriologically safe, it doesn’t remove chemical contaminants. Many people dislike the taste of iodine-treated water.


    Lastly, filtering cleans water mechanically. Travel water filters are good microfiltration unit that can remove: “harmful cocci, bacteria, protozoa, fungi, cysts, and parasites are totally removed, including the chemically resistant infectious agents of Giardia, the amoebic and shigella dysenteries, and those causing typhoid, cholera bilharzia and a long list of other dangerous diseases.” Filtration has the advantage over other methods mentioned above as it does not require chemicals. However, filters are the most expensive option out of the rest but a good filter pumps out good water in a few minutes and is reusable.

    2. Explain why desalination techniques, despite proven technological effectiveness, are not used more widely to produce potable drinking water.


    The two most common desalination techniques are distillation and reverse osmosis. Both of these require energy to remove salts from seawater or brackish water, and thus inherently are expensive. If a less expensive option is available (such as hauling fresh water from a distance), then the less expensive option is 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 likely source of lead is from solder in the pipe joints or from lead pipes themselves.

    b. Does the chemical research carried out in this chemistry building account for the elevated lead levels found in the drinking water? Why or why not?
    Research activities should not contribute to lead in the drinking water, assuming that any lead compounds are disposed of using prescribed methods. Although many undergraduate chemistry experiments used to use lead, most now have been redesigned to avoid it and other toxic metal ions completely.

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

    Only water-soluble vitamins would be expected to be polar molecules. Though a fat-soluble vitamin will often have individual polar bonds or small regions of the molecule, overall this is out-weighed by non-polar sections. Polar covalent bonds attract to water through hydrogen bonding and may allow the molecules to dissolve in water, while non-polar covalent bonds favour interactions with the non-polar chains in lipids.

Application Exercise 4: Global Climate Change


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 (W/m²), but the energy leaving Earth’s surface averages 390 W/m². Why isn’t Earth cooling rapidly?

Even though the amount of energy emitted is more than double the amount received, Earth does not cool rapidly because the atmosphere retains much of the emitted energy.

2. Describe & explain where the stamen is correct or incorrect. Explain. 


When temperature measurements are extrapolated into the future, predictions made by Arrhenius of a 5–6 °C rise in the average temperature of the planet’s surface may need to be revised. Current estimates from the United Nations predict that average temperatures will increase somewhere between 1.4 °C and 5.8 °C (2.5 °F and 10.4 °F) by the year 2100. Other scientists, looking at a possible doubling of CO 2 emissions in the future, estimate a temperature increase between 1.0 °C and 3.5 °C (1.8 °F and 6.3 °F). Future temperature changes can be influenced, at least to a considerable extent, by the human beings who inhabit this planet. We are a long way from the out-of-control hothouse of Venus, but we face difficult decisions. These decisions will be better informed with an understanding of the mechanism by which greenhouse gasses interact with radiation to create the greenhouse effect. For that, we must again take a submicroscopic view of matter. 

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


One of the first radar devices developed during World War II used microwave radiation of a wavelength that triggers the rotation of water molecules. This was unfortunate because:

i. it heated up the air around the machine.

ii. it caused diseases in the operators of the radar.

iii. absorption of microwave radiation by water in the atmosphere interferes with the detection of intended objects.

4. 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 why)?


Answers will likely depend a little on geography. Air quality will likely be the most serious short term concerns of my group, especially with the speed industrial is growing. Take a look at quality of air from Beijing, polluted by the factories or the cost saving method that result in haze and deforestation in Indonesia. The ozone hole is probably too far removed for students like us to have felt the impact directly. Depending on the perceptions of seriousness of climate change, ozone layer depletion will likely be the most serious long term concern we have.


Application Exercise 3: Energy from Combustion


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

a. A charcoal briquette burns


Exothermic. A charcoal briquette releases heat as it burns.

b. Water evaporates from your skin

Endothermic. Water absorbs the heat necessary for evaporation from your skin, and your skin feels cooler.

c. Ice melts


Endothermic. Ice absorbs the necessary heat to melt from the environment.

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


The bond energies involved are: 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. The bond energies of the products are larger than those of the reactants. This will lead to a large negative net energy change indicating an exothermic reaction.

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

Wouldn’t you rather spill a drop of hot coffee on you than the whole cupful at the same temperature? Although the drop and the cup full of coffee may initially have the same temperature, you will receive a bigger burn from the bigger volume of coffee because it has the higher heat content. Heat is a form of energy. In contrast, temperature is a measurement that indicates the direction heat will flow. Heat always flows from an object at high temperature to an object at lower temperature. This means that if hot coffee is added to cold coffee, heat will flow from the hot liquid to the cold liquid, and the final temperature of the mixture will be between the original temperatures of the two individual solutions. Heat depends on the temperature and on how much material is present.

  1. A premium gasoline available at the most stations gas an octane rating of 98. What does that tell you about:


a. The knocking characteristics of this gasoline

Gasoline with an octane rating of 98 has the same knocking characteristics as a mixture composed of 98% isooctane and 2% n-heptane. As a “premium gasoline,” it has a higher octane rating than other blends sold at gasoline stations and hence is more resistant to knocking than these blends.

b. Whether the fuel contains oxygenates

The octane rating provides no information about whether or not the fuel contains oxygenates. Other labels around the pump should reveal this information.

Ozone Layer


The ozone layer or ozone shield is a region of Earth’s stratosphere that absorbs most of the Sun’s ultraviolet (UV) radiation. It contains high concentrations of ozone (O3) in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth’s atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 kilometres (12 to 19 mi) above Earth, although its thickness varies seasonally and geographically.


The ozone layer absorbs 97 to 99 percent of the Sun’s medium-frequency ultraviolet light (from about 200 nm to 315 nm wavelength), which otherwise would potentially damage exposed life forms near the surface.

Fun Fact: The United Nations General Assembly has designated September 16 as the International Day for the Preservation of the Ozone Layer.

When was the ozone layer discovered?
The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson. Measurements of the sun showed that the radiation sent out from its surface and reaching the ground on Earth is usually consistent with the spectrum of a black body with a temperature in the range of 5,500–6,000 K (5,227 to 5,727 °C), except that there was no radiation below a wavelength of about 310 nm at the ultraviolet end of the spectrum. It was deduced that the missing radiation was being absorbed by something in the atmosphere. Eventually the spectrum of the missing radiation was matched to only one known chemical, ozone. Its properties were explored in detail by the British meteorologist G. M. B. Dobson, who developed a simple spectrophotometer (the Dobsonmeter) that could be used to measure stratospheric ozone from the ground. Between 1928 and 1958, Dobson established a worldwide network of ozone monitoring stations, which continue to operate to this day. The “Dobson unit”, a convenient measure of the amount of ozone overhead, is named in his honor.

Formation of ozone
Ozone present in the stratosphere forms a protective layer, known as ozone layer , ozonosphere or ozone umbrella. Its concentration in atmosphere is about 10 ppm. In the upper atmosphere, atmospheric gases absorbs the sun’s radiation and release molecules . In lower atmosphere , atmospheric oxygen get dissociated and subsequently combines with molecular oxygen of the upper stratosphere, thereby producing ozone.

O2—–(UV radiation)—-> O+O
O2 + O ———–> O3


Different layers of the atmosphere
(Adapted from:
To understand ozone layer, it would be helpful to know the different layers of the atmosphere. The earth’s atmosphere is composed of many layers, each playing a significant role. The first layer stretching approximately 10 kilometers upwards from the earth’s surface is known as the troposphere. A lot of human activities such as gas balloons, mountain climbing, and small aircraft flights take place within this region.

The stratosphere is the next layer above the troposphere stretching approximately 15 to 60 kilometers. The ozone layer sits in the lower region of the stratosphere from about 20-30 kilometers above the surface of the earth. The thickness of the ozone layer is about 3 to 5 mm, but it pretty much fluctuates depending on the season and geography.

Ozone layer is a deep layer in earth’s atmosphere that contain ozone which is a naturally occurring molecule containing three oxygen atoms. These ozone molecules form a gaseous layer in the Earth’s upper atmosphere called stratosphere. This lower region of stratosphere containing relatively higher concentration of ozone is called Ozonosphere. The Ozonosphere is found 15-35 km (9 to 22 miles) above the surface of the earth. The thickness of the ozone layer differs as per season and geography. The highest concentrations of ozone occur at altitudes from 26 to 28 km (16 to 17 miles) in the tropics and from 12 to 20 km (7 to 12 miles) towards the poles.

Importance of Ozone
(Adapted from:
The presence of ozone layer in the stratosphere is vital as it absorbs the ultraviolet radiation that is harmful to life and prevent them from reaching the Earth’s atmosphere .  If these radiations are allowed to reach the Earth’s atmosphere they will increase the temperature of lower atmosphere to such an extent , that it will be impossible for any life to survive on earth. In addition, these UV radiations can cause severe radiation damage in human and animals such as DNA mutation and skin cancer.

O3 + UV radiations——–> O2 + O

Depletion of Ozone
Mechanism of ozone depletion includes:
Natural process : Ozone in the upper atmosphere absorbs UV radiations of short wavelength and release atomic oxygen. This natural mechanism however do not upset the equilibrium of ozone because atmospheric oxygen absorbs UV radiation of wavelength of shorter than 240nm and photo dissociates into two oxygen atoms. This oxygen combines O2 molecules to form ozone.

Anthropogenic Process: CFCs used in refrigerants and aerosol sprays destroy ozone molecules. At the stratosphere, CFCs breaks to produce chlorine radicals. These chlorine radicals react with ozone molecules and destroy the ozone molecules in a series of reaction:

CFCl3 + UV Light ——- > CFCl2 + Cl
Cl + O3 ———– > ClO + O2
ClO + O ———– > Cl + O2

The free chlorine radical produced will react and destroy another ozone molecule again.

Ozone layer depletion

Impacts of CFCs on ozone layer

In 1985, a hole the size of the United States appeared in the ozone layer above the Antarctic. Without the ozone layer, more UV-B rays  from the sun penetrate the atmosphere with various inconvenient results, such as a massive increase in skin cancers, reduced crop productivity, depletion of fish stocks, and climate changes resulting in floods and famine.

The scientists rushed to the conclusion, over the next few years, that  the depletion of the ozone layer was due to chemicals known as chlorofluorocarbons, or CFCs, which are used in such things as aerosols, hamburger packaging and refrigerators. Most scientists agree that a reduction of 85 per cent in CFC emissions is needed immediately – just to stabilise conditions.

In  Montreal, however, the top brains from twenty-four countries decided on a reduction of only 50 per cent, and then not until 1998. Moreover, they were talking only about consumption of CFCs. In fact, they’ve actually agreed to let the big companies increase their production of CFCs.

Negative consequences of ozone depletion 
Adapted from:
Stratospheric ozone filters out most of the sun’s potentially harmful shortwave ultraviolet (UV) radiation. If this ozone becomes depleted, then more UV rays will reach the earth. Exposure to higher amounts of UV radiation could have serious impacts on human beings, animals and plants, such as the following:

Harm to human health

  • More skin cancers, sunburns and premature aging of the skin.
  • More cataracts, blindness and other eye diseases: UV radiation can damage several parts of the eye, including the lens, cornea, retina and conjunctiva.
  • Cataracts (a clouding of the lens) are the major cause of blindness in the world. A sustained 10% thinning of the ozone layer is expected to result in almost two million new cases of cataracts per year, globally (Environment Canada, 1993).
  • Weakening of the human immune system (immunosuppression). Early findings suggest that too much UV radiation can suppress the human immune system, which may play a role in the development of skin cancer.

Adverse impacts on agriculture, forestry and natural ecosystems

  • Several of the world’s major crop species are particularly vulnerable to increased UV, resulting in reduced growth, photosynthesis and flowering. These species include wheat, rice, barley, oats, corn, soybeans, peas, tomatoes, cucumbers, cauliflower, broccoli and carrots.
  • The effect of ozone depletion on the Canadian agricultural sector could be significant.
  • Only a few commercially important trees have been tested for UV (UV-B) sensitivity, but early results suggest that plant growth, especially in seedlings, is harmed by more intense UV radiation.

Damage to marine life

  • In particular, plankton (tiny organisms in the surface layer of oceans) are threatened by increased UV radiation. Plankton are the first vital step in aquatic food chains.
  • Decreases in plankton could disrupt the fresh and saltwater food chains, and lead to a species shift in Canadian waters.
  • Loss of biodiversity in our oceans, rivers and lakes could reduce fish yields for commercial and sport fisheries.

Damages to animals

  • In domestic animals, UV overexposure may cause eye and skin cancers. Species of marine animals in their developmental stage (e.g. young fish, shrimp larvae and crab larvae) have been threatened in recent years by the increased UV radiation under the Antarctic ozone hole.


  • Wood, plastic, rubber, fabrics and many construction materials are degraded by UV radiation.
  • The economic impact of replacing and/or protecting materials could be significant.