Student Text 18

C H A P T E R

Problems with the atmosphere

C H A P T E R

Problems with the atmosphere

18

Chapter 18 Problems with the atmosphere

Key Knowledge Role of the atmosphere in maintaining life in the environment

effects of human activities, such as agriculture, industry, transport, energy production, on the

atmosphere

chemical reactions and processes of acid rain

qualitative effects of ozone depletion and photochemical smog

The major contributing gases to the enhanced greenhouse effect and at least one of the associated state,

national or international protocols

Breath of lifeor death?The atmosphere is vast, but it is not so vast that the waste gases we generate can be diluted to insignificance. Human activities have pushed natural cycles, such as the carbon cycle, out of balance. As a result, global warming, air quality, acid rain and the hole in the ozone layer have become key issues.

Some of the debate on these issues has been very emotive because of the likely impact of controls on national economies, jobs and lifestyles. This situation is made all the more complex because many of those who enter the debate do not understand the chemical processes at work. In this chapter, we will consider some of the scientific research undertaken on these issues, and look at some of the underlying chemistry and the solutions that have been already been put in place.

Figure 18.1 Air quality is poor in many major cities.


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The hole in the ozone layer

OzoneOzone, O

3, is another molecular form of oxygen and so is called an

allotrope of oxygen (Figure 18.2).It is a light blue gas with a pungent odour. This odour can sometimes

be detected near photocopiers and other electrical equipment, and also after lightning, since ozone is produced when any electrical discharge passes through oxygen.

The ozone layerOzone occurs naturally in a layer within the stratosphere (Figure 17.6 on page 404). When oxygen molecules at this height are exposed to the higher energy UV (ultraviolet) radiation from the Sun, they split into separate atoms:

O2(g) 2O(g)

The oxygen atoms produced in this reaction contain an unpaired electron, which makes them highly reactive. When they collide with

an oxygen molecule, they attach themselves to it and form ozone. This requires the presence of an extra particle to absorb some of the energy released in the reaction, shown as M in the following equation, where M can be N

2, another O

2 molecule, or

other particle:

O(g) O2(g) M(g) O

3(g) M(g)

The net reaction therefore is:

3O2(g) 2O

3(g)

The concentration of ozone does not keep building up, however, because the ozone molecules absorb UV radiation of slightly different energy and split up, forming oxygen once more:

2O3(g) 3O

2(g)

If there is no interference, the rates of these two reactions are in balance and so the concentration of ozone in the ozone layer remains steady. Because both processes absorb UV radiation, only about one in 1030 parts of this particular type of radiation reaches the Earths surfacea very significant reduction! Without this protection, life on Earth would be very different.

The destruction of ozoneUnfortunately, the balance between the production and decomposition of ozone is threatened by the presence of certain chemicals in the stratosphere

at the height of the ozone layer. Two of the winners of the 1995 Nobel Prize for Chemistry, Marion Molina and Sherwood Rowland, were the first scientists to show how ozone is affected by some pollutants. The most common of these pollutants are the chlorofluorocarbons (CFCs).

A highly reactive particle that has an unpaired electron is termed a radical.

chemBYTEHow much ozone?

The concentration of the ozone in the ozone layer is only about 10 ppm (v/v). It has been estimated that if all the ozone from the Earths surface to a height of 60 km were assembled on the Earths surface, it would make a thin lm of gas only about 3 mm thick! Yet it would weigh some 3000 million tonnes!

Ozone was first discovered in 1839. Its name comes from the Greek word ozein, meaning to smell.

OO O

This shared pair has come from the centraloxygen atom only. Hence the central atomis considered to have a positive charge andthe recipient oxygen atom a negative charge.

Figure 18.2 The structural formula of ozone and a molecular model of this triatomic molecule

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Many compounds containing chlorine and bromine do not contribute to this destruction. Fluorine radicals from the CFCs do not contribute because they rapidly form hydrogen fluoride, HF, which does not attack ozone, although it is a dangerous compound in other ways (page 203).

Ozone concentration is measured in dobson units. One dobson unit (1 DU) represents one ozone molecule per billion molecules of air.

In 1974, Molina and Rowland found that when CFCs are released into the atmosphere, they move up to the stratosphere, where they are decomposed by UV radiation. This releases chlorine atoms, which contain an unpaired electron and hence are very reactive. The chlorine radicals catalyse the decomposition of ozone molecules through a series of steps, shown below. Bromine radicals, formed from the bromine atoms present in some CFCs, act in a similar way.

First step: X(g) O3(g) O

2(g) XO(g) where X Cl or Br

Second step: XO(g) O(g) X(g) O2(g)

Net reaction: O3(g) O(g) 2O

2(g)

Since the chlorine and bromine radicals are regenerated in the process and not consumed, they can go on to destroy many more molecules of ozone. These destructive radicals have a lifespan of up to 110 years. Thus each CFC molecule entering the ozone layer can cause the destruction of billions of ozone molecules!

Not all the chlorine and bromine radicals that participate in the destruction come from CFCs. About 20 per cent come from natural sources, such as chloride and bromide salts in the oceans. However, these have always been present, and so cannot be blamed for any change in ozone concentrations.

The hole in the ozone layerFollowing the work of Molina and Rowland, scientists started to notice a serious, localised decrease in the concentration of ozone in the ozone layer over Antarctica. This depletion in ozone became known as the hole in the ozone layer. This hole appears each spring, and is caused by the action of UV radiation on chlorine molecules produced on ice clouds that form in the stratosphere above Antarctica in winter. This effect also occurs at the North Pole but is not as dramatic, since the temperatures are never as low there as they are over Antarctica.

Solving the problemThe discovery of the hole in the ozone layer in 1985 and the subsequent evidence for the strong link between ozone depletion and certain chemicals produced by the chemical industry sparked intense international debate. CFCs were widely used at the time as refrigerants and as propellants for aerosol sprays, because they were very chemically stable. Under the Montreal Protocol of 1987, which was later strengthened, many countries agreed to cut CFC emissions. There is some indication that these controls

chemBYTEOops!

Long before scientists working for BAS discovered the hole, satellites had detected seasonally very low ozone concentrations, but had been programmed to discard such low readings as inaccurate, attributable to an instrumental error. It was only when the BAS ndings were published that the scientists who processed the satellite data went back and realised what the programming decision had masked.

Figure 18.3 A satellite image of the hole in the ozone layer over Antarctica in September 2005. Ozone levels are colour-coded from dark blue (lowest), through cyan and green to yellow (highest).

CFCs in actionClick on the link to CFCs in action and view the animation of the destruction of ozone by CFCs. Read more about this process.

are succeeding in protecting the ozone layer. Members of the British Antarctic Survey (BAS), who have been measuring ozone levels in the Antarctic for the past 40 years and were the first to discover the ozone hole, believe that the hole will not get much worse provided countries continue to reduce their CFC emissions. This view is supported by CSIRO scientists, who have also been at the forefront of this research.

Ozone layerClick on the link to ozone layer and view the latest NASA images of the hole in the ozone layer above the South Pole as well as for the whole globe.

1 Draw a diagram of the ozone layer and annotate it to explain how it blocks out most of the Suns UV radiation.

2 What does the fact that only the higher energy UV radiation can break up oxygen molecules and ozone molecules suggest about the

strength of the bonds within these molecules? Why might this be the case?

3 Many polymers decompose under the action of UV light. However, sunglasses are made of a polymer that is opaque to UV light.

Why is it important that our eyes are protected from this radiation?

4 The chlorofluoromethanes is a family of CFCs given the commercial name freons. Freon 12 has the formula CF2Cl

2 and CFC-12 has

the formula CF2ClBr. Draw the valence structure of each of these molecules.

5 The ozone concentration in a particular sample of air was 25 DU. What would this concentration be in:

a ppm? b %(v/v)?

6 Explain why a layer of ozone gas up in the stratosphere, which is many kilometres high, would make a layer of only 3 mm at ground level.

7 Some propellants were designed to be safe, inert, non-toxic and non-flammable for aerosol spray cans.

a Why would these properties be important for many aerosol products?

b Examine the labels on three of these products used now and state what gas has been used instead of CFCs.

c Are there any concerns about this replacement gas? Discuss.

8 Human emissions of CFCs occur mainly in the northern hemisphere. Nevertheless, the greatest hole in the ozone layer occurs over

the South Pole, not the North Pole. Explain why.

9 Ozone located in the ozone layer plays are very important, life-sustaining role. However, it is very harmful to us if we were to breathe it in.

a Name some sources of the ozone present near the Earths surface.

b Conduct a search of electronic and print media to find out what harmful effects can come from breathing in ozone, and write a

brief report.

c We still need some UV radiation to land on the Earths surface. Our skin must have some exposure to it in order to synthesise

vitamin D. Plants need it for photosynthesis. Explain why photosynthesis is the means by which we access the Suns energy for

the energy needs of our bodies.

QU E S T IONS 18 . 1

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Photochemical smogHave you noticed the brown haze present in many cities, especially on still, sunny days? This haze is termed photochemical smog because it arises from the action of sunlight on pollutants in the airprimarily nitrogen oxides and hydrocarbon vapours. There are hundreds of chemical compounds present in this smog, although the relative concentrations of these pollutants change over the day. The principal pollutants present are ozone, oxides of nitrogen (known as NO

x) and peroxyacetyl nitrate (known as PAN).

It is nitrogen dioxide, NO2, which gives the smog its brown colour (page 361).

The main source of the nitrogen oxides and hydrocarbon vapours is the exhaust gases of motor vehicles. In engines that run on hydrocarbon fuels (page 232), the hydrocarbons react with oxygen present in the air that is drawn through the combustion chamber, producing carbon dioxide and steam. This combustion is not 100 per cent efficient. Unburnt hydrocarbon vapours are swept out with these gases. In addition, in the limited oxygen supply in the combustion chamber, carbon monoxide also is produced. Moreover, although most of the nitrogen present in the air intake passes out in the exhaust gases, the temperature in the engine is high enough for the following reaction to occur:

N2(g) O

2(g) 2NO(g)

The NO, CO and unburnt hydrocarbons present in exhaust gases are described as primary pollutants. The NO

2, ozone, PAN and other compounds present in

photochemical smog are termed secondary pollutants, because they are produced from the primary pollutants through a series of complex chemical reactions in the presence of sunlight (Figure 18.5).

As shown in the nitrogen cycle (page 415), NO further reacts with oxygen in the air to produce NO2 which, like ozone, is a respiratory irritant. This in turn dissolves in moisture and rain to form nitrites and nitrates. This is a principal source of acid rain (studied next). The main products of combustion, CO2 and water vapour (steam), also present problems, since both are greenhouse gases.

Health hazardClick on the link to health hazard and read the article from the Medical Journal of Australia. What are some of the possible health effects of undertaking exercise in polluted air? What advice is given to enable people to maintain their best level of fitness?

CO, NO, unburnt hydrocarbons

sunlightenergy

verycomplexreactions

O3, NOx, PAN,other

compounds

secondary pollutants

PHOTOCHEMICALSMOG

main gases from exhaust

primary pollutants

CO2, H2O, N2

Figure 18.5 The production of photochemical smog a schematic diagram


CH3O

O

C

NO2Figure 18.4 The structural formula of PAN. This is a serious pollutant, even in low concentrations. It causes severe eye irritation and damage to plants.

National Pollutant InventoryClick on the link to National Pollutant Inventory and view the data on air pollutants. What is the most significant single source of pollutants in Australia, other than that from industrial facilities? What are the pollutants to which we are most exposed? Why is there great concern about mercury

emissions into the air? What is their main source? Are human activities the only sources of these pollutants?

Acid rainWe have already considered one main source of acid rain, sulfur dioxide, the damage this can cause and how this can be controlled to some extent (page 339). The other principal source is nitrogen oxide, NO, which is produced by high-temperature combustion engines in motor vehicles, agricultural machinery, diesel trains and aircraft, as well as many industrial machines and fossil fuel power stations. Nitric acid is produced from NO by a series of reactions:

In air: 2NO(g) O2(g) 2NO

2(g)

In water vapour and rain: 3NO2(g) H

2O(l) 2HNO

3(aq) NO(g)

These reactions are part of the nitrogen cycle (page 415). The problem is that human activities produce excessive amounts of nitrogen oxides and nitric acid, which damage the environment and pose a major threat to human health and safety. This is exacerbated by the fact that our atmosphere can so swiftly carry these and other pollutants around the globe (Figure 18.6).

According to CSIRO Division of Atmospheric Research and the EPA, acid rain is not a significant problem in Victoria. Of greater concern is the build-up of ozone in summer and of particulate matter from smoke (mostly in winter).

Figure 18.6 Why the management of airborne pollution is difficult

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Solving the problemAlthough NO is produced naturally during lightning, and SO

2 is produced in

volcanic activity, clearly if we are to address the problem of acid rain, not to mention photochemical smog, we need to prevent the release of the oxides of nitrogen and sulfur from human activities. Ideally, we should lower our demand for energy and, where possible, avoid using motor vehicles. Industry should follow the principles of green chemistry and develop alternative processes which do not produce NO

x, SO

x and other

atmospheric pollutants.Where these gases are produced, however, the waste gases should be

treated to remove as much NO and other pollutants as possible before they are emitted into the air. Catalytic converters, fitted to the exhaust system of motor vehicles, represent one such solution (Figure 18.7). These provide a catalytic surface on which CO and NO are converted to CO

2 and

N2, respectively. However, although

their use has achieved a significant reduction in the concentrations of CO, NO and unburnt hydrocarbons, catalytic converters are not without their drawbacks. For example, the catalyst surface can become poisonedthat is, deactivated by certain pollutants.

chemBYTEGrass pollution

It has been known for some time that the cooking of hamburgers and fries in our huge takeaway food industry is a major source of airborne unburnt hydrocarbons. Now CSIRO scientists have discovered that mowing our lawns also can release hydrocarbons into the air! We may need to consider growing grasses that do not need to be mown so often! This is being researched in other countries as well!

QU E S T IONS 18 . 21 Acid rain contains one or more of sulfurous acid, sulfuric acid or nitric acid. These are produced in chemical reactions of SO

x and NO

x

with water.

a Explain what is meant by the formulas SOx and NO

x.

b Identify two natural sources of acid rain.

c Outline one problem that results from acid rain.

d Coal-fired power stations emit both SOx and NO

x. Explain why both are present in the waste gases emitted from the huge

furnaces in which coal is burnt.

e Name at least one other source of each of SOx and NO

x from human activities.

f Give two reasons why these gases can rapidly move from one country to another.

2 a Distinguish between the kind of smog that occurred in London in 1952 and photochemical smog in terms of their chemical

composition and the conditions that lead to their formation.

b Design a simple flow chart for the production each type of smog.

c Explain why each type of smog presents serious health problems.

d Describe one chemical solution to each type of smog.

3 List four ways in which the emission of waste gases such as SOx and NO

x can be prevented or reduced according to the principles of

green chemistry.continues on next page

Figure 18.7 Inside a catalytic converter

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The enhanced greenhouse effectWhen radiation from the Sun reaches Earth, some is reflected back into space by atmospheric particles, liquid and ice particles in clouds and the Earths surface itself. Some radiation is absorbed before it reaches the Earths surface, not only by the ozone layer (page 422) but also by water vapour. Even so, a vast amount of solar energy reaches the Earths surface. Despite this, the Earths surface does not get hotter and hotter because it continually radiates heat energy, in the form of infrared radiation, into the atmosphere. This heat transfer to the atmosphere occurs because the Earths surface has a higher temperature than the atmosphere.

Certain gases in the atmosphere, known as greenhouse gases, absorb much of this infrared radiation and get hotter. They radiate some of this radiation back to the Earths surface. As a result, the mean surface temperature is 16 C, 33 C higher than that of the Moon, and the temperature range is far less than that on the Moon, which is the same distance from the Sun.

The greenhouse effectThe greenhouse effect is the greenhouse-like (or blanket-like) trapping of some of the infrared radiation from the Earths surface by the greenhouse gases

Aerosol researchClick on the link to aerosol research. See the latest images from NASA of various massive events that have spread particulate pollutants across the globe by clicking on each part of the image library

at the bottom (Dust, Smoke, Ash and Todays Aerosols) in turn. Read about the different types of

aerosols detected by the TOMS instruments. What does the acronym TOMS represent? Explore more

of this website.

continued from previous page

4 Write an equation for the action of nitric acid on marble, CaCO3, and calculate what mass of nitric acid

would be required to dissolve 20.0 g marble.

5 The emission of pollutant gases from certain industries can be reduced by methods such as electrostatic

precipitation to remove dust, and the use of activated charcoal (which absorbs certain gases) and giant

fabric filters (Figure 18.8). Investigate one of these solutions or else catalytic converters. Find out how it

works, as well as its advantages and disadvantages.

6 In your view, how should environment authorities, the manufacturing industry and individual

community members address the problems of photochemical smog and acid rain? What are the major

limitations of bandaid solutions such as catalytic converters?

Figure 18.8 The Bag House, Eraring Power Station, NSW. The thousands of filter bags act like giant vacuum cleaner bags, removing almost all the particulate matter from the waste gases.

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(Figure 18.9). It is a naturally occurring and life-sustaining process that has occurred on Earth for millions of years. Were it not for the moderating influence of the greenhouse gases on the temperature of the Earths surface, life as we know it could not exist. The greenhouse gases include methane, water vapour, carbon dioxide and ozone.

Ozone absorbs about3% of the Suns energy.

H2O

O3

The atmosphere radiates heat energy into space.

EARTH

The Earth absorbs about48 (that is, almost half)of the Suns energy.

Atmospheric particles and liquid andice particles in clouds and on theEarths surface reflect about 31 ofthe Suns energy back into space.

Water vapour absorbs about18% of the Suns energy.

Greenhouse gases absorb some of the heat energy from the Earth and radiate the rest back to Earth and out into space.

The Earth radiatesheat energy into theatmosphere.

greenhouse gases

Figure 18.9 A schematic representation of the greenhouse effect

Global warmingOver millions of years, natural cycles have controlled the concentration of greenhouse gases in the atmosphere. There were processes that produced them and processes that removed them. But then humans started to engage in large-scale activities such as generating electricity by burning coal and other fossil fuels, clearing huge areas of forests to grow crops and graze ruminant animals (which burp out vast quantities of methane), running agricultural and other machinery on fossil fuels, manufacturing concrete, glass, steel, aluminium and so on, and transporting people and goods.

These activities have significantly increased the concentration of greenhouse gases in the atmosphere to way beyond their natural levels (Figure 18.10). Figure 18.11 shows the increase in concentrations of methane, which is a far more potent greenhouse gas than is carbon dioxide.

The enhanced greenhouse effect is the trapping of additional infrared radiation from the Earths surface by the increased concentration of greenhouse gases. It is of concern, since there is now evidence that it is causing a gradual increase in the Earths average surface temperature. This phenomenon is commonly known as global warming or climate change.


Added to this is the additional heating of the atmosphere by large cities and huge industrial complexes. Studies have shown that as they are much hotter than the surrounding land, they radiate significant heat into the atmosphere.

Possible consequencesBased on their present understanding of the atmosphere, and on the assumption that the worlds population, and hence its energy consumption, will continue to increase, atmospheric scientists have predicted that there will be an increase of between 0.8 and 2.0 C in the Earths surface temperature by 2030. Possible consequences of this temperature increase include:

Change in the climate of each part of the globe. This would affect our water resources, the type of agriculture that is possible in each region, and the health of all living species. There could be an expansion of tropical regions, which means a larger proportion of the worlds population could be exposed to malaria and other deadly tropical diseases. Most of Australia is likely to be drier, however.

Rise of sea level, principally from the expansion of the upper levels of water in the oceans as their temperature rises, leading to flooding of low-lying areas.

Solving the problemAs a result of increasing scientific evidence that global warming is occurring, since 1979 a number of international summits have been held on climate change. It has been acknowledged that action needs to be taken, especially by highly industrialised countries, which are major contributors to the problem. This has been strengthened by the international agreement known as the Kyoto Protocol, which lists emissions target commitments for developed countries.

Large amounts of methane gas are produced at the Werribee Sewage Treatment Plant as bacteria break down organic matter. This gas is collected and burnt to generate electricity. Although this produces another greenhouse gas, carbon dioxide, this is less harmful, as methane is a far more potent greenhouse gas than carbon dioxide.

Figure 18.10 Human activities have increased the output of greenhouse gases.

All animals including humans, give some CH4due to fermentation. Termites produce a significant amount.

Grazing ruminant animals each belch up 300L per day!

Landfill (decay): organic material breaking down in the absence of oxygen

Biomassburning

Coal mines, natural gas fields

Marshes Rice paddies

Fertilisers Combustion

Seecarboncycle

Note:These are the principal greenhousegases produced in human activities

N2OCO2CH4H2O

vapour

Some scientists believe that the consequences of global warming will not be as dire as this. They question the computer models on which many predictions have been based and argue that more data needs to be accumulated and more sophisticated computer models need to be constructed before the predictions can be considered reliable.

1980 1985 1990 1995 2000

1700

ppb

1600

1500

Methane (CH4)

Figure 18.11 Methane concentrations (in parts per billion) measured at the Cape Grim Baseline Air Pollution Station in Tasmania (Source: CSIRO)

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QU E S T IONS 18 . 31 In 1996, the Bureau of Transport and Communications Economics, an advisory body to the Australian government, released a paper

on the projected cost of absorbing the carbon dioxide from motor vehicles by using trees. If rapidly growing trees such as Pinus

radiata were planted, it was predicted that the cost would be $2 per tonne of CO2 emitted in the year 2000 and $5 per tonne per

year by the year 2015. The calculations were based on the fact that a typical modern car emits about 7 tonnes of CO2 per year.

Absorbing the total amount of CO2 would require the planting of 100 000 hectares of trees per year, reaching up to about two

million hectares by the year 2015.

a Write an equation to show how trees absorb CO2.

b The trees would have to be replaced every few years, since only rapidly growing trees consume significant CO2: in mature trees,

the rate of absorption of CO2 just balances the rate at which it is produced in cellular respiration. What might be another

advantage of this practice?

c What might be one drawback of this tree-planting solution?

d What other strategies could reduce the amount of CO2 from cars, without resorting to so much tree planting?

continues on next page

Article 2 of the Kyoto Protocol includes the following statements:

Each Party included in Annex I, in achieving its quantified emission limitation and reduction commitments under Article 3, in order to promote sustainable development, shall: a Implement and/or further elaborate policies and measures in

accordance with its national circumstances, such as: i Enhancement of energy efficiency in relevant sectors of the

national economy; ii Protection and enhancement of sinks and reservoirs of greenhouse

gases not controlled by the Montreal Protocol, taking into account its commitments under relevant international environmental agreements; promotion of sustainable forest management practices, afforestation and reforestation;

iii Promotion of sustainable forms of agriculture in light of climate change considerations;

However, there are many problems to be resolved. For example, not all major greenhouse emitters are signatories. Although this does not necessarily mean that these countries are not implementing strategies to help address the issue of global warming, clearly there needs to be a resolution of the difficulties they have with the Protocol. Most scientists are arguing that concerted action by all countries to curb greenhouse emissions is vitaland urgent!

Australian scientist sounds warningClick on the link to Australian scientist sounds warning. Read the paper on The changing composition of the global atmosphere by Dr David Etheridge, a highly respected Australian scientist, presented at a symposium held by the Australian Academy of Science. What are Dr Etheridges

credentials for speaking on this subject? What issues and concerns does he raise? How can changes in the atmosphere be monitored? What actions

does he think are necessary if we are to successfully manage the global atmospheric environment?

431

continued from previous page

2 Figure 18.12 shows the results of studies of ice core samples taken at Vostok, Antarctica.

Age (thousands of years) Present

CO2 (

ppm

v)

Chan

ge in

atm

osph

eric

tem

pera

ture

(C)

160 120 80 40 0

180

200

220

240

260

280

10.0

7.5

5.0

2.5

0

2.5

CO2

C

Figure 18.12 The graph of the Vostok ice core studies of the variations in temperature and carbon dioxide concentrations in the atmosphere in the past 160 000 years

a Is there any evidence in the graph to suggest that there is a direct relationship between temperature and carbon dioxide

concentrations in the atmosphere? Discuss.

b Explain the difference between the greenhouse effect and the enhanced greenhouse effect, and their impact on the viability of

life on this planet.

3 Investigate the issue of global warming using electronic and print media and prepare a multimedia report in terms of:

a the gases contributing to the problem, their sources, and which of these gases are causing the most concern

b the predicted consequences if the mean temperatures of the atmosphere and oceans rise, and the myths that need to be

dispelled

c current research on the issue

d the Kyoto Protocol and solutions that have begun to be implemented, the solutions you would regard as bandaid measures and

those that might be classed as preventative

e proposals for future action, particularly in Australia and what is hindering this process.

18.1

432 Unit 2


increased risk ofskin cancers,

cataracts, damageto plants

increased rate of corrosion of metals,

and of deterioration ofmarble, concrete etc.

damage to plants and ecosystems

increased UV exposure

change of climate,flooding of

coastal regions etc.

unburnt hydrocarbons,NO, CO from motor vehicles

particulate matterand other pollutants

Cl and Br radicalsfrom aerosols

SOx and NOx fromburning fossil fuels,industrial processes etc.

SOx from metalextraction

healthproblems

POOR AIR QUALITY

PHOTOCHEMICALSMOG

GLOBALWARMING

ACID RAINHOLE IN THE OZONE LAYER

THE IMPACT OF HUMANACTIVITIES ON THE ATMOSPHERE

CO2, H2O, CH4, N2Ofrom industrial andagricultural activities

Visual summary

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Key termsenhanced greenhouse effect

(global warming, climate change)hole in the ozone layer radical

greenhouse effect photochemical smog secondary pollutants

greenhouse gases primary pollutants

Review questions1 Nitrous oxide is the common name of dinitrogen oxide, N

2O. It is an important greenhouse gas because it does not easily

break down and has an atmospheric lifetime of more than a century. Although two-thirds of N2O emissions are from natural

sources such as oceans and soils, the concentration of N2O in the air is increasing because of land-use changes, biomass

burning, fertiliser use and some industrial processes. This is shown in Figure 18.13.

a Explain what is a greenhouse gas and how it acts.

b Name three other examples of greenhouse gases

and state one major source of each.

c Use the graph to estimate the approximate

percentage increase in N2O concentration from

1980 to 2000.

d Is the emission of increasing amounts of

greenhouse gases the only cause of global

warming? Discuss.

2 Another oxide of nitrogen is nitrogen oxide, NO,

which has the common name nitric oxide. This gas

is involved in the formation of acid rain and the

production of photochemical smog, and it can destroy

ozone.

a Write equations for the reactions that occur in the ozone layer in which ozone undergoes a natural cycle of being

produced and broken down. Explain why these reactions require high-energy UV radiation.

b NO is emitted by the engines of supersonic aircraft which fly at the height of the ozone layer. Explain why this would be

of concern.

c Write an equation for the production of NO in motor vehicles and explain why the reaction can only take place at high

temperatures.

d What term is used to describe the type of pollutant NO is when it is emitted by motor vehicles?

e What is photochemical smog and how is this gas involved in its formation?

f The ice clouds that form in the stratosphere above Antarctica each winter, and which are involved in the production of

the chlorine that is involved in the depletion of the ozone layer above Antarctica, contain crystals of water and nitric acid.

Write the equation for the reactions in which nitric acid is produced from NO in the atmosphere.

3 Methane is such a potent greenhouse gas that one solution to the problem of global warming in Victoria has been to collect this

gas from landfill, the Werribee Sewage Treatment Plant and other sources and burn it to generate electricity, even though the

products of the reaction are also greenhouse gases. This methane is produced by bacteria acting on the rubbish and sewage.

a Write the balanced equation for the combustion of methane in air.

b What potential might this have as a practical global solution to the enhanced greenhouse effect? Discuss.

WO

R D

18 18

1980 1985 1990 1995 2000

312

ppb

308

304

300

Nitrous oxide (N2O)

Figure 18.13 Nitrous oxide concentrations measured at the Cape Grim Baseline Air Pollution Station in Tasmania (Source: CSIRO)

PrefaceAcknowledgementsKey knowledge gridContentsUnit 1 The Big Ideas of ChemistryArea of Study 1 The Periodic TableChapter 1: An introduction to chemistryThe philosophers stoneThe alchemists of ChinaThe great forensic mystery

The alchemists of India and TibetThe alchemists of EgyptAlchemy and Western scienceThe elementsThe origins of atomic theoryThe age of enlightenmentSceptical chemistsThe Lavoisiers

The discovery of chemical lawsThe difference between a compound and a mixture

John Daltons model of the atomVisual summaryKey termsReview questions

Chapter 2: The structure of the atomCathode raysLight or particles?

The discovery of the electronDalton was wrong!

The Thomson plum pudding modelThe alpha-particle scattering experimentThe experimentThe resultsExplaining the results

The Rutherford nuclear modelHow big is the nucleus?The electrons

Problems with the Rutherford nuclear modelSpectral evidence

The Bohr model of the atomElectron shells

Explaining spectra using the Bohr modelReturning to the ground stateElectron configurationsChembox: The discovery of the protonAtomic numberWhy Z?

Problems with the Bohr modelLimitations to drawings of Bohrs model

The Schrdinger modelThe subshellsAtomic orbitals

Electron configurations using the Schrdinger modelThe energies of the subshellsA sample electron configurationGiving an electron its address

Visual summaryKey termsReview questions

Chapter 3: The masses of atomsAtomic weightsTables of atomic weights

Weight and massWhat do you really weigh?

IsotopesMass spectra

Discovering the neutronMass numbers and symbols of isotopesThe relative mass scaleUnits of the relative mass scale

Relative atomic massRelative molecular massTheoretical percentage compositionApplying percentage compositionVisual summaryKey termsReview questions

Chapter 4: The modern Periodic TableDbereiners triadsThe cylinder of elementsThe Law of OctavesMendeleev and MeyerMissing elements found!Meyers workRecognition

Periodic tablesThe modern Periodic TableFeatures of the Periodic Table

The periods of the Periodic TableThe groups of the Periodic TableThe blocks of the Periodic TableThe s-blockThe p-blockThe d-block

The noble gasesCavendishs bubbleThe lazy oneWhere there is one The new group

The missing elementsThe transuranium elementsVisual summaryKey termsReview questions

Chapter 5: Trends of the Periodic TableMetallic and non-metallic characterGold a unique metalThe in-between elementsHydrogen the unique non-metal

Classes of compoundsChembox: Puzzling out the structures of substancesOxides of the elementsClasses of oxidesTrends in the oxides of the elements

Other compounds of the elementsReactive and unreactive elementsUnreactive elementsThe most reactive element of allThe most reactive metals

Trends in reactivities of the elementsViolent reactions

Explaining the trends in reactivityTrends in first ionisation energies

The reactivity of Group 1 metalsSize mattersReductants

Trends in electronegativitiesAcross a periodUp a groupExplaining the reactivity of fluorine


Chapter 6: Measurement in chemistryIntroducing the moleWhy this particular large number?

Relating number of moles to number of particlesParticles in packagesMolar massRelative masses of ionic compounds and ionsIons

Theoretical composition by mass of ionic compoundsRelating number of moles to massDetermining empirical formulasDeducing an empirical formula

Chembox: PheromonesDegree of hydration of hydrated saltsVisual summaryKey termsReview questions

Area of Study 2 MaterialsChapter 7: MetalsClues from the properties of metalsThe metallic latticeThe sodium ion

Explaining some properties with the modelProperties determined by bonding forcesMelting point and boiling pointDispelling mythsHardness

Metallic bondingFrom one extreme to another

Density of metalsLimitations to the metallic modelVersatile copperObtaining copperCopper alloysCopper in the seaCopper in cars

Chembox: Very smart materialsChemical reactivities of metalsChoosing the right metalVisual summaryKey termsReview questions

Chapter 8: Ionic compoundsThe properties of ionic compoundsThe formation of sodium chloride crystalsModelling the sodium chloride latticeExplaining why sodium chloride is brittleExplaining sodium chlorides electrical propertiesExplaining sodium chlorides chemical stability

Limitations to the modelOther ionic compoundsNaming ionic compounds

Polyatomic ionsWriting formulas from the charges on the ionsThe charges on the ionsWriting empirical formulas

Chembox: Smart new materialssynthetic bonesVisual summaryKey termsReview questions

Chapter 9: The non-metalsThe hydrogen moleculeHow tiny is that?How does the molecule hold together?

The fluorine moleculeThe oxygen moleculeWhen oxygen atoms meet

The sulfur moleculeCarbon the wonder elementDispersion forcesOther molecules

DiamondExplaining the tetrahedral structure

Explaining the properties of diamondHardness and melting pointThermal conductivityElectrical conductivity

GraphiteThat odd electronWhy the flat triangles?

Explaining the properties of graphiteHardness and melting pointElectrical conductivity

Chembox: BuckyballsNanotubesChemical reactivityThe non-metalsThe chemically stable elementsThe chemically reactive elements


Chapter 10: Molecular compoundsHydrogen fluorideThe hydrogen fluoride molecule

Water H2OThe molecule

Chembox: Ammonia the molecule of EgyptMethaneThe molecule

Properties of molecular compoundsMolecular compounds

Polar and non-polar moleculesNon-polar molecules

Hydrogen bondingLarge molecules

Water the unique moleculeWhy water expands when it freezesWhy water can support objects on its surfaceWhy ammonia is so soluble in waterSoaps

The wheel-shaped moleculesVisual summaryKey termsReview questions

Chapter 11: Organic compoundsWhat are organic compounds?Families of organic compoundsThe family of alkanesBuilding up the familyHomologous series

The properties of the alkanesExplaining the propertiesReaction with chlorine gasCombustion of the alkanesViscosity

Structural isomersSystematic naming of alkanesThe alkene familyThe gas that ripens fruit

The properties of the alkenesStructural isomers of alkenesAddition reactionsReaction with chlorineReaction with hydrogenReaction with bromineReaction with itself!

Why carbon is uniqueVisual summaryKey termsReview questions

Chapter 12: Designer materialsPlastics are not all plastic!Classes of polymerDesigner plasticsCrystalline regionsBranchingPlasticisers and other additivesPlasticisersStabilisers

Side groupsBenzene ringsSome different polymers

Other structural featuresSpatial orientationFoamingChain length

CopolymersRubberSynthetic rubbersSilicone rubbersA very smart invention

Cross-linked polymersResins

BiopolymersSurface tension and surface energyTotal surface energySurface area to volume ratio

Creating nanomaterialsCreating nanopowdersCreating nanodevices

Chembox: Molecular scaffoldsVisual summaryKey termsReview questions

Unit 2 Environmental ChemistryArea of Study 1 WaterChapter 13: WaterWater the unique substanceThe properties of waterCapillary actionWater the ultimate heat bankSpecific heat capacityWhy the difference?Why this property is crucial

Water the coolerApplications of this property

Water the solventIdentifying true solutionsFlocculationThe Tyndall effect

Solutions, colloids and suspensionsAqueous solutions

The solution processDissolving ionic solidsMolecular solids

Factors influencing solubilityThe forces operatingEnergy factorsTemperatureChemical reactions

Writing equations for solutionsMolecular substancesIonic compounds

Precipitation reactionsPredicting the formation of precipitatesMeasuring solubilityUnsaturated solutionsSupersaturated solutions

Water in crisisDistillationLiquid solutesPurifying local water

Chembox: Affordable desalinationReverse osmosisVisual summaryKey termsReview questions

Chapter 14: Acidbase and redox reactionsReactions in the environmentAcids and basesThe LowryBrnsted theoryConjugate pairsStrengths of acids and basesStrengths of acidsThe conjugate bases of acids

Water the acid and basePolyprotic acidsSulfuric acidPhosphoric acid

Amphiprotic substancesAcidbase indicatorsReactions of acidsAcid and an oxideAcid and a hydroxideAcid and a carbonateAcid and a hydrogen carbonateNeutralisation reactionsAcid and a metal

Redox reactionsStrength of metals as reductantsMetal displacement reactionsThe half-equationsPredicting reactions

An introduction to galvanic cellsThe salt bridgeThe electrodesThe circuit

Corrosion of ironSlowing down corrosion

Chembox: Acid rainVisual summaryKey termsReview questions

Chapter 15: Quantities in chemistryMolarityCalculating the molarity of a solution

Everyday concentration unitsUsing different concentration unitsDilution of solutionsThe dilution formula

An introduction to stoichiometryMassmass stoichiometryMassvolume stoichiometryVolumevolume stoichiometry for solutionsTitrationsThe pH scalepH calculationsChembox: Making the most of dairy wasteVisual summaryKey termsReview questions

Chapter 16: Green chemistryThe twelve principles of green chemistryGetting off to a safe startThe case of adipic acid

Using renewable resourcesThe case of diesel

Atom economyThe case of the analgesic ibuprofen

Chembox: Polyacrylate (PAC)Halogenated solventsSolventsVolatile organic compoundsPERC

Supercritical carbon dioxideThe use of surfactants

Putting out firesAlternative pest controlOrganochlorine compoundsOrganophosphates and carbamatesReduced risk pesticides

'Green bleachesVisual summaryKey termsReview questions

Area of Study 2 The AtmosphereChapter 17: The atmosphereThe atmosphereEssential gases of the atmosphereOxygenCarbon dioxideNitrogenWaterOzone

The layers of the atmosphereThe cold trap

OxygenStructure and bondingIsotopes and abundanceThe properties of oxygenMonitoring oxygen concentrations

The production of oxygenThe laboratory production of oxygenThe commercial production of oxygen

Oxidation numbersIdentifying the oxidant and reductantThe carbon cycleThe properties of carbon dioxideWhy is carbon dioxide so unreactive?

The nitrogen cycleVisual summaryKey termsReview questions

Chapter 18: Problems with the atmosphereBreath of life or death?The hole in the ozone layerOzoneThe ozone layerThe destruction of ozoneThe hole in the ozone layerSolving the problem

Photochemical smogAcid rainSolving the problem

The enhanced greenhouse effectThe greenhouse effectGlobal warmingPossible consequencesSolving the problem


Chapter 19: Measuring gasesChaotic gasesThe kinetic theory of gasesThe origin of the kinetic molecular theoryEffect of temperature changesForces between particlesExplaining the properties of gasesIdeal gases and real gases

Gas pressureBoyles lawCharless lawThe combined gas equationStandard conditions for gases

Molar volumesThe general gas equationGas stoichiometryVolumevolume stoichiometry for gasesVisual summaryKey termsReview questions

AppendicesAppendix 1: The relative atomic masses of the elementsAppendix 2: Guidelines for using significant figuresAppendix 3: Common ions, ion colours, flame colours and solubilitiesAppendix 4: Common units of measurementAppendix 5: Writing chemical equationsAppendix 6: Relative acid strengthsAppendix 7: Relative strengths of oxidants and reductants

AnswersGlossaryIndex

Student Text 18

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