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SULFUR

( eg SO2)

GROUP 16(AS)

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Sources of SO2

1. From human activity : egs

a. combustion of fossil fuel/petroleum Proteins in plants and animals consist of

amino acids. Certain amino acids contains S

Eg : cystine and methionine

Plants & animals decaycompressed byhigh pressure & tempforms fossil fuel

Petroleum burned in airS oxidised to SO2

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b. Contact process

c. manufacture of cement or bricks d. coal power stations

FeS present in coal is oxidised to SO2

CaO is used to absorb and prevent the SO2from being released into the atmosphere

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2. From natural sources: egs

a. volcanoes b. rotting vegetation and plankton

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Acid Rain

1. Role of SO2:

a. Acid rain: rain having pH less than 5.6 b. One of the chief culprit in formation of acid

rain is SO2released into the atmosphere

c. SO2+ moisture + O

2forms H

2SO

4

Eqn : 2SO2+ 2H2O + O22H2SO4

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2. Effects of acid rain :

a. kills fishes in lakes :

SO4

2-in acid rain combines with aluminium

in complex compounds (eg clay) to form

solubleAl2(SO4)3

This washes into streams where it interferes with

the operation of fish gills which becomes cloggedwith mucus.

Fishes die from lack of oxygen

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b. damage to trees and crops :

i) Al3+

poisons trees ii) essential nutrients are washed from soil.

Trees starve to death.

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c. corrodes or damages

i) buildings ( contains limestone or marbleCaCO3 )

ii) metallic structures eg bridges , ships and

motor vehicles

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Uses of SO2

1. Manufacture of H2SO4(Contact Process)

a. sulfur is burned in air S + O2 SO2 , H = exothermic

b. further oxidation :

2SO2 + O2

2SO3 ,

H = exothermic

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Conditions :

catalyst

V2O5, vanadium (V) oxide 4500C , 1 - 2 atm

c. SO3absorbed in 98% H2SO4

SO3 (g) + H2SO4(l)

H2S2O7 oleum

H2S2O7 (l) + H2O (l) 2H2SO4(l)

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Note : SO3is notabsorbed in water

Equation : SO3(g) + H2O (l) H2SO4(l) Reason :

Reaction is intensely exothermicas to

vaporise H2

SO4

formed(fumes are corrosive)

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Industrial importance of H2SO4:

Manufacture of fertilisers , detergents ,pigments , synthetic fibres and organic

chemicals ( eg dyestuff and explosives )

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2. As a preservative :

a. SO2is an inorganic food additive Eg : soft drinks . wine , soups , preserved

vegetables or fruits ( apricots , raisins )

Function of SO2

:

To kill or inhibit growth of yeast / fungi /

micro-organisms/bacteria

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b. cooked and processed food contains carbonyl

compounds

SO2is a reducing agent( anti oxidant) thereforeretard oxidation of food

Eg : Prevents alcohols and carbonyl compound (

aldehydes ) in food from being oxidised and

forming sour-tasting acids

Note : SO32-(sulfites) are also used in food

preservation