Topic 2:Topic 2: Elemental and Environmental Elemental and Environmental

ChemistryChemistry2.1 The Periodic Table2.2 Cycles in Nature (Carbon Cycle,

Nitrogen cycle & Fertilizers)2.3 Greenhouse Effect2.4 Acid Rain2.5 Photochemical Smog2.6 Water Treatment2.6 Water Treatment

2.2: Cycles in Nature 2.2: Cycles in Nature Carbon and Oxygen CycleCarbon and Oxygen Cycle

A complex series of processes through which all A complex series of processes through which all of the small molecules and inorganic ions in of the small molecules and inorganic ions in existence rotate so as to maintain their presence existence rotate so as to maintain their presence in the atmosphere.in the atmosphere.

The processes involved are: The processes involved are: Decomposition of organic compoundsPhotosynthesis by plantsAerobic respiration Combustion activities

Decomposition: Organic matter contain Organic matter contain C, N, P, S elements which elements which

make up biological compounds: carbohydrates, make up biological compounds: carbohydrates, proteins, fats and oils,…proteins, fats and oils,…

Organic matter decomposed through 2 conditions:Organic matter decomposed through 2 conditions:

Aerobic AnaerobicPresence of O2 Absence of O2

Produces:Carbon dioxide, CO2

Nitrate ions, NO3-

Sulfate ions, SO42-

Phosphate ions, PO43-

Produces:Methane, CH4

Ammonia, NH3

Hydrogen sulfide, H2S

Phosphine, PH3

Photosynthesis: Green plants convert COGreen plants convert CO22 to glucose. to glucose. Chlorophyll in leaves act as catalystChlorophyll in leaves act as catalyst 6 CO2 + 6 H2O → C6H12O6 + 6 O2

Respiration: Derive energy from burning of glucose.Derive energy from burning of glucose. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy

Under specific conditions, organisms that do not fully Under specific conditions, organisms that do not fully decay formed decay formed carbon based fuels ( (coal, oils and and natural gas) over a slow and time consuming process over a slow and time consuming process taking several million years. COtaking several million years. CO22 is then release into is then release into atmosphere when these carbon based fuel undergo atmosphere when these carbon based fuel undergo combustion. Eg combustion of petrol produces CO2 and H2O. C8H18 + 25/2 O2 → 8 CO2 + 9 H2O

sunlight

Click on the website below for detailed information about carbon cycle, its animated!• http://www.ebex21.co.nz/enlargement.asp• http://bcs.whfreeman.com/thelifewire/content/chp58/

5802002.html• http://epa.gov/climatechange/kids/carbon_cycle_vers

ion2.html• http://www.wildbc.org/publications-resources/climate

change/greenhouse-effect-part2.pdf

Check out the games offer in these sites regarding carbon cycle, its fun:• http://www.windows.ucar.edu/earth/climate/carbon_c

ycle.html

In atmosphere, nitrogen occurs as In atmosphere, nitrogen occurs as diatomic diatomic moleculesmolecules, , NN≡N, N≡N, N22 ≈78% (Why so much?) ≈78% (Why so much?)

Inert / lack reactivity and and not soluble in water. Explain why atmospheric nitrogen is inert. (2m) - - triple covalent bonded (strong bond)triple covalent bonded (strong bond) - - lots of energy is require to break itlots of energy is require to break it State why the plants cannot absorb atmospheric

nitrogen directly. (1m) - Plants can only absorb nitrogen in the form of - Plants can only absorb nitrogen in the form of

nitrate ions (soluble form) to make protein.

Therefore nitrogen gas must be converted either naturally or artificially into nitrates ions.

Nitrogen CycleNitrogen Cycle

NaturallyNaturally Biological process with the help of soil bacteria with the help of soil bacteria

Nitrogen fixing bacteria convert nitrogen convert nitrogen compounds (Ncompounds (N22) that is insoluble into its water ) that is insoluble into its water soluble form ammonia gas then later to ammonium soluble form ammonia gas then later to ammonium compounds. (compounds. (Nitrogen fixation process))

N2 → NH3 → NH4+

Nitrifying bacteria will then convert NH will then convert NH44++ into nitrite into nitrite

ions then nitrate ions via two steps, nitrate ions will ions then nitrate ions via two steps, nitrate ions will then be absorb by plants. (then be absorb by plants. (Nitrification process))

NH4+ → NO2

- → NO3-

Nitrosomonas nitrobacter

Rhizobium

Lightning discharges/ forest fires/ volcanic eruption High energy / temp in these events is sufficient to break the in these events is sufficient to break the

strong triple covalent bond in strong triple covalent bond in NN22 leading to reaction between leading to reaction between atmospheric nitrogen with atmospheric oxygen to form nitric atmospheric nitrogen with atmospheric oxygen to form nitric oxide.oxide. N2 + O2 → 2 NO

Nitric oxide will then react with more atmospheric oxygen to Nitric oxide will then react with more atmospheric oxygen to produce nitrogen dioxideproduce nitrogen dioxide 2 NO + O2 → 2 NO2

Nitrogen dioxide will dissolves in water to form nitric acid and Nitrogen dioxide will dissolves in water to form nitric acid and nitrous acid.nitrous acid. 2 NO2 + H2O → HNO2 + HNO3

Nitric acid ionises in water to produce nitrate ions Nitric acid ionises in water to produce nitrate ions HNO3 + H2O → H3O+ + NO3

-

ArtificiallyArtificially Industrial process to produce nitrogen fertilizer to produce nitrogen fertilizer

Haber process: atmospheric nitrogen is used to Haber process: atmospheric nitrogen is used to manufacture ammonia gas.manufacture ammonia gas. N2 + 3 H2 → 2 NH3

Production of fertilizer: ammonia gas react with nitric Production of fertilizer: ammonia gas react with nitric acid to form ammonium nitrate. acid to form ammonium nitrate. NH3 + HNO3 → NH4NO3

Fertilizer dissociates in soil water produces nitrates.Fertilizer dissociates in soil water produces nitrates. NH4NO3 + aq → NH4

+ + NO3-

Human activities that produces high heat energythat produces high heat energyHeat from internal combustion of engines and and

industrial smelters/ furnaces will provide sufficient will provide sufficient energy to cause the energy to cause the surrounding atmospheric surrounding atmospheric nitrogennitrogen to react with atmospheric oxygen. to react with atmospheric oxygen.

Click on the website below for detailed information about nitrogen cycle!http://www.biology.ualberta.ca/facilities/multimedia/

uploads/intro-biology/ncycle.swfhttp://www.nodvin.net/snhu/SCI219/demos/Chapter

_3/Chapter_03/Present/animations/32_2_1a.htmlhttp://trc.ucdavis.edu/biosci10v/bis10v/media/ch30/

nitrogen_cycle_v2.html

Check out the games offer in these sites regarding nitrogen cycle:http://www.naturenextdoor.org/PDF%20Files/thenite

cycle.pdfhttp://www.studystack.com/matching-1457

Fertilizer Fertilizer Plants need soluble nitrogen in the form of Plants need soluble nitrogen in the form of NO3

- (nitrate ion) to synthesize proteins, amino to synthesize proteins, amino acids, DNA, RNA, nucleic acidsacids, DNA, RNA, nucleic acids…. ….

While soluble phosphorous in the form of While soluble phosphorous in the form of H2PO4-

(dihydrogen phosphate ion) is required is required to to synthesize nucleic acids, ADP and ATPsynthesize nucleic acids, ADP and ATP..

Fertilizers: chemical compound added into soil Fertilizers: chemical compound added into soil to to increase soil fertility.increase soil fertility.

Fertilizer must be Fertilizer must be soluble in water (nutrients (nutrients can be absorbed).can be absorbed).

Organic fertilizer:Organic fertilizer: cow dung, cow dung, human feaces, bone/blood, guano.human feaces, bone/blood, guano.

Inorganic fertilizer:Inorganic fertilizer: Nitrogen fertilizers are synthesized from ammonia are synthesized from ammonia

(through Haber process) with any strong acid.(through Haber process) with any strong acid.2 NH2 NH33 + H + H22SOSO44 → (NH → (NH44))22SOSO44

NHNH33 + HCl → NH + HCl → NH44ClCl

Phosphorus fertilizer: Phosphate rock (bird : Phosphate rock (bird droppings insoluble in water) is heated with sulfuric droppings insoluble in water) is heated with sulfuric acid to form superphosphate.acid to form superphosphate.

CaCa33(PO(PO44))2(s) 2(s) + 2H+ 2H22SOSO4(aq)4(aq)→ 2CaSO→ 2CaSO4(s)4(s)+Ca(H+Ca(H22POPO44))22

Excessive usage of fertilizer, will leads to , will leads to Nutrients NONutrients NO33

- - - flow into pond or lake (still water)- flow into pond or lake (still water) Cause a sudden growth of algae - Cause a sudden growth of algae - algae bloom Algae bloom cause the Algae bloom cause the depletion of oxygen and and

light blocking on the pond or lake; eventually no on the pond or lake; eventually no life can live in the water. life can live in the water.

A type of water pollution: A type of water pollution: Eutrophication

Excess nitrate ions (not absorb by plants) will Excess nitrate ions (not absorb by plants) will undergo denitrifying process, converting nitrate ion undergo denitrifying process, converting nitrate ion to nitrogen gas or nitrous gas (inert)to nitrogen gas or nitrous gas (inert) NONO33

-- → → NN22 / / N2O Nitrous oxide in the lower atmosphere will cause Nitrous oxide in the lower atmosphere will cause

enhanced greenhouse effect..

http://coseenow.net/2008/11/eutrophication-animation/

Eutrophication

2.3 Greenhouse Effect (GHE)2.3 Greenhouse Effect (GHE)Natural GHE – maintain steady temperature in Earth’s atmosphereSolar radiation contains mostly UV radiation, with

shorter wavelength is re-radiate from Earth surface as infra-red (IR) radiation, with longer wavelength.

Part of the infra-red radiation (radiant heat) will be absorbed / trapped by greenhouse gases (CO2, CH4, CFC, N2O, O3 and H2O - in the lower atmosphere) to keep Earth surface warm.

The rate at which heat is trapped by the atmosphere equals the rate at which heat is lost from the atmosphere.

Enhanced GHE The The increase concentration of GH gases resulted

from human activities (through industrial & (through industrial & agriculture sector), agriculture sector),

lead to an lead to an increased in the absorption / trapping of infra-red radiation / heat,

which in turn is responsible for which in turn is responsible for an increase in the Earth’s overall temperature; thus causing global ; thus causing global warming.warming.

Sources of GH gasesGH gas

Main source Human activity

CO2 Excessive Excessive combustion of fossil combustion of fossil fuelsfuels

Transport, power Transport, power production, burning of production, burning of rainforest, land clearingrainforest, land clearing

CH4 Anaerobic Anaerobic breakdown of breakdown of organic materialsorganic materials

Excessive livestock Excessive livestock farming of cattle and farming of cattle and sheep, rice growing sheep, rice growing

N2O Denitrification of Denitrification of nitrates by microbesnitrates by microbes

Excessive usage of Excessive usage of nitrogenous fertilizers in nitrogenous fertilizers in agricultureagriculture

Melting of polar ice caps, increases sea-level: Melting of polar ice caps, increases sea-level: cause flooding of low-lying/ coastal areacause flooding of low-lying/ coastal area

Erratic climate and weather changes: Erratic climate and weather changes: e.g. El Nino and La Ninae.g. El Nino and La Nina

Increase pest population: drop in crop yieldIncrease pest population: drop in crop yield Disrupt aquatic food chain, ecosystem: kill Disrupt aquatic food chain, ecosystem: kill

planktons/ fishes/ corals that are heat sensitive planktons/ fishes/ corals that are heat sensitive Increase multiplication of bacteria: increase Increase multiplication of bacteria: increase

occurrence of epidemicsoccurrence of epidemics

Effects of enhanced GHE

Reduce excessive emission of GH gasesReduce excessive emission of GH gases

CO2 re-forestation, use alternative fuel source, use alternative energy, car pool, use public transportation

CHCH44 No solutionNo solution

NN22OO Educate farmers to use just enough fertilizerEducate farmers to use just enough fertilizer

CFCCFC Find substitution or banFind substitution or banHH22OO No solution (out of control)No solution (out of control)

OO33 A strong oxidant which presence in low A strong oxidant which presence in low concentration in the lower atmosphere, concentration in the lower atmosphere, negligible (will not cause enhanced GHE)negligible (will not cause enhanced GHE)

Solutions

Click on the website below for detailed information about greenhouse effect, its animated and fun!http://

earthguide.ucsd.edu/earthguide/diagrams/greenhouse/

http://epa.gov/climatechange/kids/global_warming_version2.html

http://www.sciencemuseum.org.uk/energy/site/EIZInfogr9.asp

http://www.wildbc.org/publications-resources/climatechange/greenhouse-effect-part2.pdf

http://www.planetguide.net/book/chapter_3/greenhouse1.html

2.4 Acid Rain Rain is Rain is naturally acidic, between , between pH 5.6 - 6.5, due , due

to to dissolves carbon dioxide forming carbonic acid..CO2 + H2O → H2CO3

Carbonic acid (weak acid) Carbonic acid (weak acid) ionises partially in water in water to produce low concentration of hydronium ions.to produce low concentration of hydronium ions.

H2CO3 + H2O H3O+ + HCO3-

Acid rain: rain water with a : rain water with a pH value less than 5.6,, is formed from human activities that produces is formed from human activities that produces oxides of nitrogen and / or and / or oxides of sulfur into into troposphere.troposphere.

** pH: : a measure of the concentration of hydrogen / a measure of the concentration of hydrogen / hydronium ions in mol/L { hydronium ions in mol/L { pH = -log10 [H+] / [H3O+] } }

pH calculation: pH = -log10 [H+] / -log10 [H3O+] pOH = -log10 [OH-] pH + pOH = 14

1.1. Calculate the pH of 1.2 x 10Calculate the pH of 1.2 x 10-3-3 mol/L HCl mol/L HCl solution.solution.

2.2. Calculate the pH of 0.1 x 10Calculate the pH of 0.1 x 10-3-3 mol/L NaOH solution. mol/L NaOH solution. 3.3. Calculate the [HCalculate the [H++] of nitric acid solution with a pH of 2.9.] of nitric acid solution with a pH of 2.9.4.4. Calculate the pH of sulfuric acid when [Calculate the pH of sulfuric acid when [HH33OO++] = 3.8 x ] = 3.8 x

1010-3-3 mol/L. mol/L.5.5. Calculate the pH of KOH solution when the [OHCalculate the pH of KOH solution when the [OH--] in the ] in the

solution is 2.1 x 10solution is 2.1 x 10-3-3 mol/L. mol/L.

Acid rainAcid rain due to due to Oxides of nitrogen (NOx)1. High energy provided causes atmospheric nitrogen react with provided causes atmospheric nitrogen react with

oxygen forming nitric oxide.oxygen forming nitric oxide.• Natural phenomena: lightning discharges, volcanic activity, Natural phenomena: lightning discharges, volcanic activity,

forest fires.forest fires.• Human activities: internal combustion of engine, industrial Human activities: internal combustion of engine, industrial

smelters / furnaces. smelters / furnaces. N2 + O2 → 2 NO

2.2. Nitric oxide continue to react with more oxygen forming nitrogen Nitric oxide continue to react with more oxygen forming nitrogen dioxide. dioxide. 2 NO + O2 → 2 NO2

3.3. Nitrogen dioxide then dissolve in water vapor to form nitric acid Nitrogen dioxide then dissolve in water vapor to form nitric acid and nitrous acid.and nitrous acid. Nitric acid then ionises completely to release Nitric acid then ionises completely to release high [H+], therefore , therefore pH < 5.6. 2NO2 + H2O → H+ + NO3

- + HNO2

Acid rainAcid rain due to due to Oxides of sulfur (SOx)1.1. Activities below causes the formation of sulfur dioxideActivities below causes the formation of sulfur dioxide

Natural phenomena: forest fire, volcanic activities Natural phenomena: forest fire, volcanic activities (burning of sulfur containing compounds)(burning of sulfur containing compounds) S organic matter + O2 → SO2

Human activities:Human activities: Burning of carbon based fuel which contain S as Burning of carbon based fuel which contain S as

impuritiesimpurities S carbon based fuel + O2 → SO2

Roasting of sulfide ore in the during production of Roasting of sulfide ore in the during production of metal in industrial, eg. Production of zinc starts of metal in industrial, eg. Production of zinc starts of by roasting of zinc sulfideby roasting of zinc sulfide

2 ZnS + 3 O2 → 2 ZnO + 2 SO22.2. In atmosphere, sulfur dioxide slowly reacts with In atmosphere, sulfur dioxide slowly reacts with

atmospheric oxygen to form sulfur trioxide.atmospheric oxygen to form sulfur trioxide. 2 SO2 + O2 → 2 SO3

3.3. Sulfur dioxide and sulfur trioxideSulfur dioxide and sulfur trioxide dissolves in rain water dissolves in rain water to form sulfurous acid and sulfuric acid, respectively. to form sulfurous acid and sulfuric acid, respectively. SO2 + H2O → H2SO3 SO3 + H2O → H2SO4 (1)

Sulfurous acid and sulfuric acid ionises in water to Sulfurous acid and sulfuric acid ionises in water to produce Hproduce H++ which leads to acid rain. which leads to acid rain.Sulfurous acid ionises partially in water to produce low Sulfurous acid ionises partially in water to produce low concentration of Hconcentration of H++ ions. ions. H2SO3 H+ + HSO3

-

Sulfuric acid ionises completely in water to produce Sulfuric acid ionises completely in water to produce high concentration of H+ ions.. H2SO4 → 2 H+ + SO3

2- (2)OR

SO3 + H2O → 2 H+ + SO32-

Effect of acid rain1.1. Leach essential mineralsLeach essential minerals (nutrients) from topsoil (nutrients) from topsoil

Fe2O3 + 6 H+ → 2 Fe3+ + 3 H2O2.2. Mobilisation of toxic cationsMobilisation of toxic cations such as aluminium such as aluminium

Al2O3 + 6 H+ → 2 Al3+ + 3H2O

3.3. Erode limestone structuresErode limestone structuresCaCO3 + 2 H+ → Ca2+ + H2O + CO2

4.4. Corrode metallic structuresCorrode metallic structuresFe + 2 H+ → Fe2+ + H2

5.5. Killing pH sensitive aquatic lifeKilling pH sensitive aquatic life in rivers/ lakes/ in rivers/ lakes/ 6.6. Lower the pH of soil, growth of vegetation will be Lower the pH of soil, growth of vegetation will be

stunted, crop yield decreasestunted, crop yield decrease

Solutions Cut down the emissions of NOx and SOx

1.1. Treat industrial waster by liming the smoke stack Treat industrial waster by liming the smoke stack using ‘using ‘scrubber’ containing solid alkali such as ’ containing solid alkali such as calcium oxide (lime).calcium oxide (lime).

CaO + SO2 → CaSO3

2.2. Use Use catalytic converter in cars in cars2CO + 2NO → 2CO2 + N2

3.3. Use cleaner fuel (less sulfur content) Use cleaner fuel (less sulfur content) 4.4. Use alternative source of energy eg. solar energy… Use alternative source of energy eg. solar energy…

When acid rain already falls into lake water, When acid rain already falls into lake water, liming can can be done to neutralises the Hbe done to neutralises the H++ in the lake water. in the lake water. CaO + 2 H+ → Ca2+ + H2O

Check out the these animated websites about acid rain:http://www.epa.gov/acidrain/education/site_students/

whatisacid.html (by EPA, highly recommended! Detailed explanation about acid rain, including games)

http://www.youtube.com/watch?v=RP-sU8i2edo&feature=related

http://www.yteach.co.uk/page.php/resources/view_all?id=air_oxygen_nitrogen_Earth_argon_carbon_dioxide_water_UV_temperture_solar_space_atmosphere_page_5&full=1&w_size=1024&h_size=768

2.5 Photochemical Smog2.5 Photochemical Smog Lower atmosphere air pollutionLower atmosphere air pollution Photochemical = chemical reaction involve sunlight; Photochemical = chemical reaction involve sunlight;

smog = smoke + fogsmog = smoke + fog Major cause: Major cause: motor vehicles

CausesCauses1. Primary pollutants: : emitted directly into atmosphere

• NO - - Heat from the internal combustion of Heat from the internal combustion of engines/ industries can activate nitrogen in the air engines/ industries can activate nitrogen in the air to react with oxygen in the air to form nitric oxide.to react with oxygen in the air to form nitric oxide.

• Unburnt Hydrocarbons (HC) - - Incomplete Incomplete combustion of fossil fuel produces unburnt HCcombustion of fossil fuel produces unburnt HC

2. Secondary pollutants: : formed when primary pollutants undergo further chemical reactions

• NO form will continue to react with oxygen to NO form will continue to react with oxygen to form nitrogen dioxide, form nitrogen dioxide, NO2 2 NO + O2 → 2 NO2

In the presence of In the presence of sunlight (UV),sunlight (UV), nitrogen will nitrogen will undergo undergo photolysis ( (photochemical dissociation reaction) to form nitric oxide and monoatomic to form nitric oxide and monoatomic oxygen (radical).oxygen (radical).

NO2 → NO + O•• Monoatomic oxygen will then react with Monoatomic oxygen will then react with

atmospheric oxygen to form troposhperical atmospheric oxygen to form troposhperical ozone, O3 in the presence of sunlight. in the presence of sunlight.

O• + O2 → O3

• When unburnt HC will react with nitrogen dioxide When unburnt HC will react with nitrogen dioxide and ozone to form and ozone to form peroxy acyl nitrate (PAN) anan oxidant.oxidant.

CxHy + NO2 + O3 → CxHy.NO2.O3• Some unburnt HC eg. propane can be oxidised Some unburnt HC eg. propane can be oxidised

by ozone to formby ozone to form aldehyde. CH3CH2CH3 + O3 → CH2=CHCHO + 2H2O

acrolein

In the In the presence of sunlight and when the and when the air is stale (temperature inversion) all these all these gases will hover around / accumulate in one gases will hover around / accumulate in one area →area → Photochemical Smog..

Harmful EffectThe formation of ozone:The formation of ozone:• Affect human’s health: cause coughing, wheezing Affect human’s health: cause coughing, wheezing

and constriction and irritation of the bronchial and constriction and irritation of the bronchial respiratory system.respiratory system.

• Attack double bonds in polymers, causes cracking.Attack double bonds in polymers, causes cracking.• Plants - photosynthesis rate reduces.Plants - photosynthesis rate reduces.The formation of NOThe formation of NO22: lead to acid rain.: lead to acid rain.Presence of smog (yellowish) – low visibilityPresence of smog (yellowish) – low visibility

Solutions1.1. Use Use catalytic converter in car’s exhaust in car’s exhaust

• Oxidise CO to Oxidise CO to CO2 and reduce NO to and reduce NO to N2 2 CO + 2 NO → N2 + 2 CO2

2.2. Use alternative source of energy (long term)Use alternative source of energy (long term)3.3. Car pool, use public transportation (short term)Car pool, use public transportation (short term)

Daily Chemical Transformations Occurring in the Formation of Photochemical Smog.

Photochemcial smog

Check out the webpage below for further information about PCS: http://www.montereyinstitute.org/courses/AP%20En

vironmental%20Science/course%20files/multimedia/lesson77/animations/5a_Photochemical_Smog.html

http://www.yteach.co.uk/page.php/resources/view_all?id=pollution_air_atmosphere_carbon_dioxide_greenhouse_effect_sulphur_acid_rain_smog_ozone_layer_CFC_page_3&full=1&w_size=1024&h_size=768 [short video: detailed explanation about the components of automobile exhaust, formation of PCS and using catalytic converter to prevent PCS]

http://www.rbolen.com/bio225/downloads/photochemical_anim.swf