oxygen and ozone chemistry 222.pdf

Chemistry about oxygen and ozone

1. OXYGENAND OZONECHEMISTRY
BY
SUNIL

2. Oxygen(O2)
It is a nonmetallicchemical elementof Group 16 of theperiodic table.
Itis a colourless, odourless, tastelessgasessential to living organisms,
It taken up by animals, which convert it tocarbondioxide; plants, in turn,utilizecarbon
dioxideas a source of carbon and return the oxygen to the atmosphere.
It is a colourless, odourless, tastelessgasessential to living organisms, being taken up
by animals, which convert it tocarbondioxide; plants, in turn, utilizecarbon dioxideas
a source of carbon and return the oxygen to the atmosphere.
Its most importantcompoundiswater.

3. Occurrence and properties of oxygen
At 46% of the mass, oxygen is the most plentiful element inEarth’s crust.
The proportion of oxygen by volume in the atmosphere is 21% and by weight
inseawater is 89 %.
In rocks, it is combined with metals and nonmetals in the form of oxides that are
acidic (such as those ofsulfur, carbon,aluminum, and phosphorus) or basic (such as
those of calcium,magnesium, and iron) and as salt like compounds that may be
regarded as formed from the acidic and basic oxides, as sulfates, carbonates,
silicates,aluminates, and phosphates.
Plentiful as they are, these solid compounds are not useful as sources of oxygen,
because separation of the element from its tight combinations with themetalatoms
is too expensive

4. Isotopes
Natural oxygen is a mixture of threestable isotopes.Theyare oxygen-16,
oxygen-17, and oxygen-18
Several artificially prepared radioactive isotopes are known.
The longest-lived, oxygen-15(124-second half-life), has been used to study
respiration in mammals.
Allotropy
Oxygen has two allotropic forms, diatomic (O
2) and triatomic(O
3, ozone).
The properties of the diatomic form suggest that six electrons bond the atoms and
two electrons remain unpaired, accounting for theparamagnetismof oxygen.
The three atoms in theozonemolecule do not lie along a straight line.
Ozone may be produced from oxygen according to the equation:
3O2 2O3

5. ozone
The name ozone comes from the Greekozein, for "to smell".
It is an allotropic form of oxygen having three atoms in each molecule, formula O
3.
It is, in standard state, a pale blue, highly poisonous gas with a strong odour. Liquid
ozone is a deep blue and strongly magnetic.
Ozone is formed when an electric spark is passed through oxygen, and causes a
detectable odournear electrical machinery.
The commercial method of preparation consists of passing cold, dry oxygen
through a silent electrical discharge.
Ozone is much more active chemically than ordinary oxygen and is a better
oxidisingagent.
It is used in purifying water, sterilisingair, and bleaching certain foods.

6. Physical Properties of Ozone
Ozone is a colourlessor pale blue gas.
Ozone is slightly soluble in water and much more soluble in inert non-polar solvents likesulphuric
acid, carbon tetrachlorideor fluorocarbons that forms a blue solution.
The boiling and the melting point of ozone is−112Cand−193.2Crespectively.
Chemical Properties of Ozone
Ozone dissolves in water resulting in the formation ofhydrogen peroxide.
O
3+ 3H
2O → 3H
2O
2
Ozone reacts with lead sulfide resulting in the formation of lead sulfate.
3PbS + 4O
3→ 3PbSO
4

7. Ozone Reactions
Ozone reactions mostly take place in the atmosphere, as the unstable molecule
reacts in sunlight. These are described inLow Level OzoneandHigh Level Ozone.
There are a group of compounds calledOzonides, which are formed during the
reaction of ozone with alkali metal hydroxides, formally containing the O
3
-
ion.
An ozonideis also the unstable compound formed by the addition of ozone to the
C=C bond in alkenes. Ozone is also a very strong oxidisingagent.
2Fe
2+
+2H
+
+ O
3 2Fe
3+
+H
2O+O
2
Ozonolysisis a reaction of alkenes with ozone.
Ozone can be produced in the lab using a machine called an ozonator.
This ozone is passed through a solution of the alkene, first producing an ozonide.
This ozonideis subsequently reduced, giving the result of cleavage around the double
bond, with an oxygen attached to each carbon from the double bond.

8. 1) High-Level Ozone
The majority of ozone in the earth's atmosphere is found in the stratosphere(15-50km
above the earth's surface) This high level ozone plays a crucial role, protecting animals
and plants from the suns harmful ultra violet rays, and stabilisingthe earth's climate.
This ozone layer is incredibly unstable, since it is constantly being formed and broken
down through interactions with UV radiation. But, as it is so reactive the ozone layer can
easily be broken down by pollutant gases rising from the earth.

9. Ozone absorbs UV radiation in its formation and breakdown: O
2
absorbs UV light to form 2 oxygen
radicals:
O
2
+hv O +O (1)The oxygen radicals can then react in one of three ways:
O + O
2
O
3
(2)
O + O O
2
(3)
O + O
3
2O
2
(4)
Reaction 2 is of course the reaction in which ozone is produced. This ozone can absorb ultra-violet
radiation of wavelength 10.1-14.0 x 10
14
Hz and undergo photodissociation:
O
3
+hv O
2
+ O(5)
It is this reaction which is the most vital in shielding the earth from the sun's UV radiation

10. The Breakdown of Ozone
Here chlorine will be used as the example:
When CFC's are destroyed they form Clradicals. These chlorine radicals react with ozone:
Cl+O
3 O
2+ClO (6)
The ClOformed is another reactive free radical, which can react with oxygen atoms.
ClO+O Cl+O
2(7)
O+O
2 O
3
So, reaction 4 and 6 are competing with each other to remove oxygen from the stratosphere. the
rate of reaction of ozone with Clis over 1500 times greater than that of the one with O atoms.
Another important consideration is that the Clatoms are regenerated in reaction 7, so are a catalyst
which can go on to break down more and more ozone

11. Low Level Ozone
It is also known as surface-level ozone and troposphericozone, is a trace gas in
the troposphere (the lowest level of the Earth's atmosphere), with an average
concentration of 20–30 parts per billion by volume (ppbv), with close to 100 ppbvin
polluted areas.
ozone–oxygen cycle
Theozone–oxygen cycleis the process by whichozoneis continually regenerated
inEarth'sstratosphere, convertingultraviolet radiation(UV) intoheat. In 1930Sydney
Chapmanresolved thechemistryinvolved. The process is commonly called theChapman
cycleby atmospheric scientists.

12. Ozone–oxygen cycle
1.Oxygen photolyzedto atomic oxygen
2. Oxygen and ozone continuously
interconverted. SolarUVbreaks down
oxygen; molecular and atomic oxygen
combine to form Ozone.
3. Ozone is lost by reaction with atomic
oxygen (plus other trace atoms).

13. Chemistry
1) Creation:
An oxygen molecule is split (photolyzed) by higher frequency UV light (top end
ofUV-B,UV-Candabove) into two oxygen atoms
O
2+ ℎν
(<242nm)→ 2O
Each oxygen atom then quickly combines with an oxygen molecule to form an
ozone molecule:
O + O
2→ O
3

14. 2) The ozone–oxygen cycle:
The ozone molecules formed by the reaction above absorb radiation having an appropriate
wavelength betweenUV-CandUV-B.
The triatomicozone molecule becomes diatomic molecular oxygen plus a free oxygen atom
O
3+ ℎν
(240–310nm)→ O
2+ O
The atomic oxygen produced quickly reacts with another oxygen molecule to reform ozone:
O + O
2+ A → O
3+ A
where A denotes another molecule or atom, like N
2or O
2which is needed in the reaction as
otherwise energy and momentum wouldn't be conserved:
There is an excess energy of the reaction which is manifested as extrakinetic energy.
These two reactions form the ozone–oxygen cycle, in which the chemical energy released when O
and O
2combine is converted into kinetic energy of molecular motion.
The overall effect is to convert penetrating UV-B light into heat, without any net loss of ozone.

15. O
3+ O → 2 O
2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O
2
O
3+ O → 2 O
2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O
2
O
3+ O → 2 O
2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O
2
O
3+ O → 2 O
2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O
2
O
3+ O → 2 O
2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O
2
O
3+ O → 2 O
2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O
2
Removal:
if an oxygen atom and an ozone molecule meet, they recombine to form two oxygen
molecules:
O
3+ O → 2 O
2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O
2
The overall amount of ozone in the stratosphere is determined by a balance between
production by solar radiation and removal.
The removal rate is slow, since the concentration of free O atoms is very low.

16. Conclusion:
The ozone–oxygen cyclekeeps the ozone layer in a stable balance while protecting the lower
atmosphere from UV radiation
References:
-https://www.britanica.com/science/oxygen
-https://www.chm.bris.au.uk/motm/ozone/chem.htm
-https://en.wikipedia.org./wiki/mainpage

17. Thank you-):