Atmosphere and Enviroment

8/8/2019 Atmosphere and Enviroment

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AIRVolume Composition of gases

present in dry air.Nitrogen : 79%

Oxygen : 20%

Noble gases : 1% (mainly argon)Carbon dioxide : 0.03%


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Expt. to determine the % by volume

of oxygen in air

(1) Set up the apparatus as shown.

(2) Record the total volume of air in both

syringes.(3) Heat the copper powder (must be in

excess, why?To use up oxygen in air)

strongly with a Bunsen burner. Pass the airback and forth over the hot copper until

there is no further change in volume.


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Expt. to determine the % by volume

of oxygen in air

Eqn: 2Cu(s) + O 2(g) p 2CuO(s)

(4) Allow the apparatus to cool to roomtemperature. Why?

To measure the final volume of air at thesame temperature as the initial

volume.(5) Record the total vol. of gas left in the

syringe.


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Combustion a reaction in which a substance reacts

with oxygen with the production ofheat. If flame is produced duringcombustion, the process is calledburning.


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Combustion of elementsMany elements burn in oxygen to produce

oxides.For examples: Carbon

burns with bright red glow

produces a colourless & odourless gas Product is carbon dioxide, CO2


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Combustion of elementsSulfur

burns with a blue flame

produces colourless & pungent gas

Product is sulfurdioxide, SO2Magnesium

burns with a very bright white flame

produces white solid

Product is magnesium oxide, MgO


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Combustion of elementsCopper

Powder burns with a dull red glow produces black solid

Product is copper(II) oxide, CuO


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9/28

Combustion of Hydrocarbons

Complete combustion

If there is plenty of oxygen,hydrocarbons burn to produce carbondioxide and water and thecombustion is complete.

For example:

CH4 (g)+2O2(g)pCO2(g) + 2H2O (g)


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Combustion of HydrocarbonsIncomplete combustion

If there is limited oxygen, the combustion is

incomplete, carbon monoxide and carbonparticles (soot) are produced.

Equations:

2CH4 (g) + 3O2(g) p2CO (g) + 4H2O (g)CH4 (g ) + O2(g) p C(s ) + 2H2O (g)


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CARBON CYCLEThe removal of carbon dioxide from theatmosphere

Photosynthesis is the principal means by whichcarbon dioxide is removed from theatmosphere. The green leaves from the plantsuse energy from the sun to convert the carbon

dioxide in the air and the water from the soilinto glucose and oxygen.

Eqn: 6CO2 + 6H2OpC6H12O6 + 6O2


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The return of carbon dioxide to

the atmosphere

Respiration by plants and animals

Respiration is an energy releasing reaction

which involves the breaking down of glucoseto form carbon dioxide and water. Thisreaction provides energy for both plants andanimals and returns carbon dioxide to the

atmosphere.Equation :

C6H12O6 + 6O2 p6CO2 + 6H2O


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The return of carbon dioxide to

the atmosphereCombustion

Combustion ofcarbon-containing substances such aswood, natural gas and coal produce carbon dioxide.

Eg: C(s) + O 2(g) pCO2(g)

Links:

http://www.bbc.co.uk/schools/gcsebitesize/biology/livingthingsenvironment/2energyandnutrienttransferrev4.shtml

http://epa.gov/climatechange/kids/carbon_cycle_version2.html


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THE OZONE HOLEOzone gas

surrounds the Earth about 40 km abovethe ground

absorbs harmful ultraviolet radiation(which may cause skin cancer) from the

sun.


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THEOZONE HOLEChlorofluorocarbons (CFCs)

were used as aerosol propellants and coolant

fluids for refrigerators and air conditioners. are long-lived because they are unreactive in

the lower atmosphere.

were decomposed by sunlight when high up

in the atmosphere to produce chlorineatoms. The chlorine atoms destroy theozone molecules and deplete the ozone layer.


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GLOBAL WARMING Carbon dioxide, methane and other

greenhouse gases in the air trap heat

radiation from sun and prevent much of itescaping into space.

An increase in amount of greenhouse gaseswill trap more heat and hence the earth

becomes hotter. This temperature rise iscalled global warming or the greenhouseeffect.


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GLOBAL WARMINGConsequence

1)Expansion of water andm

elt

ing ofpolar ice p rise in sea level p flood

2) Big climatic changes p poor harvestof crops p serious food shortages.


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AIR POLLUTANTS

(Sulfur Dioxide)(i) Source

Volcanoes and combustion of fossil fuels

which contain small amount of sulfur. Forexample, burning ofcoal in power stations.

(ii) Harmful effect

sulfur dioxide in air reacts with oxygen andwater to form sulfuric acid.

Eqn: 2SO2 + 2H2O + O2 p 2H2SO4


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AIR POLLUTANTS

(sulfur Dioxide)sulfuric acid dissolves in rain water, causingacid rain which corrodes buildings, attacksmetals and kills aquatic plants and animals.

(iii) Treatment/Preventionsulfur dioxide from chimney gases isabsorbed by calcium carbonate before

the gases are released into the air.Equation : SO2 + CaCO3p CaSO3 + CO2


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AIR POLLUTANTS

(Carbon Monoxide)(i) Source

Incomplete combustion of carbon containingsubstances. For example, incompletecombustion of petrol in car engine.

(ii) Harmfuleffect

Carbon monoxide combines readily withhaemoglobins in the blood and prevents theblood from absorbing oxygen. This will lead totiredness, headaches and even death.


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AIR POLLUTANTS

(Carbon Monoxide)Carbon monoxide is dangerous as it iscolourless and odourless, thereby

giving no warning of its presence.

(iii) Treatment/Prevention

Carbon monoxide produced in car enginecan be oxidized to carbon dioxide bycatalytic converters.


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AIR POLLUTANTS

(Oxides of Nitrogen)(i) Source

Produced by reaction between oxygen andnitrogen in air at high temperature (duringlightning and in car engine)

Eqns: N2(g) + O2(g) p 2NO (g)

2NO (g) + O 2(g) p 2NO2(g)

(ii) Harmful effectNitrogen dioxide in air reacts with oxygen andwater to form nitric acid.

Eqn: 4NO2 + O2 + 2H2O p 4HNO3


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AIR POLLUTANTS

(Oxides of Nitrogen)Nitrc acid dissolves in rain water, causing acid

rain which corrodes buildings, attacks metals

and kills aquatic plants and animals.

Nitrogen dioxide also produces ozone, another

pollutant which irritates eyesand lungs.


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AIR POLLUTANTS

(Oxides of Nitrogen)(iii) Treament/Prevention

Oxides of nitrogen produced in car

engine can be reduced by fitting cars withcatalytic converters.

The oxides of nitrogen are reduced to

harmless nitrogen gas.Equation: 2CO + 2 NO pN2 + 2CO2


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AIR POLLUTANTS

(Unburnt hydrocarbons)

(i) Harmful effect

Produces ozone which irritates eyes andlungs.

(ii) Treatment/Prevention

Can be oxidized to carbon dioxide andwater by catalytic converters.


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AIR POLLUTANTS

(Ozone)(i) Harmful effect

Irritates eyesand lungs.


Reduce vehicle emissions of pollutants by

the

use of catalytic converters.


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AIR POLLUTANTS

(Methane)(i) Harmful effect

Contributes to greenhouse effect.


No easy solution.


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Additional Readings Ozone depletionhttp://www.atm.ch.cam.ac.uk/tour/http://www.beyonddiscovery.org/content/view.article.asp?a=73

Global warminghttp://www.epa.gov/globalwarming/kids/gw.htmlhttp://en.wikipedia.org/wiki/Global_warming

Air pollution

http://www.environment.nsw.gov.au/envirom/princairpol.htmhttp://www.lenntech.com/FAQ-air-pollution.htm

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