Chemistry about oxygen and ozone

1. OXYGEN AND OZONE CHEMISTRY
BY
SUNIL

2. Oxygen(O2)
 It is a nonmetallic chemical element of Group 16 of the periodic table.
 It is a colourless, odourless, tasteless gas essential to living organisms,
 It taken up by animals, which convert it to carbon dioxide; plants, in turn,utilize carbon
dioxide as a source of carbon and return the oxygen to the atmosphere.
 It is a colourless, odourless, tasteless gas essential to living organisms, being taken up
by animals, which convert it to carbon dioxide; plants, in turn, utilize carbon dioxide as
a source of carbon and return the oxygen to the atmosphere.
 Its most important compound is water.

3. Occurrence and properties of oxygen
 At 46% of the mass, oxygen is the most plentiful element in Earth’s crust.
 The proportion of oxygen by volume in the atmosphere is 21% and by weight
in seawater is 89 %.
 In rocks, it is combined with metals and nonmetals in the form of oxides that are
acidic (such as those of sulfur, 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 the metal atoms
is too expensive

4. Isotopes
 Natural oxygen is a mixture of three stable isotopes.They are 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 (O2) and triatomic (O3, ozone).
 The properties of the diatomic form suggest that six electrons bond the atoms and
two electrons remain unpaired, accounting for the paramagnetism of oxygen.
 The three atoms in the ozone molecule 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 Greek ozein, for "to smell".
 It is an allotropic form of oxygen having three atoms in each molecule, formula O3.
 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 odour near 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
oxidising agent.
 It is used in purifying water, sterilising air, and bleaching certain foods.

6. Physical Properties of Ozone
 Ozone is a colourless or pale blue gas.
 Ozone is slightly soluble in water and much more soluble in inert non-polar solvents like sulphuric
acid, carbon tetrachloride or fluorocarbons that forms a blue solution.
 The boiling and the melting point of ozone is −112C and −193.2C respectively.
Chemical Properties of Ozone
 Ozone dissolves in water resulting in the formation of hydrogen peroxide.
O3 + 3H2O → 3H2O2
 Ozone reacts with lead sulfide resulting in the formation of lead sulfate.
3PbS + 4O3 → 3PbSO4

7. Ozone Reactions
 Ozone reactions mostly take place in the atmosphere, as the unstable molecule
reacts in sunlight. These are described in Low Level Ozone and High Level Ozone.
 There are a group of compounds called Ozonides, which are formed during the
reaction of ozone with alkali metal hydroxides, formally containing the O3
- ion.
 An ozonide is also the unstable compound formed by the addition of ozone to the
C=C bond in alkenes. Ozone is also a very strong oxidising agent.
2Fe2++2H++ O3 2Fe3++H2O+O2
 Ozonolysis is 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 ozonide is 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 stabilising the 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: O2absorbs UV light to form 2 oxygen
radicals:
O2 + hv O + O (1) The oxygen radicals can then react in one of three ways:
O + O2 O3 (2)
O + O O2 (3)
O + O3 2O2 (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 1014Hz and undergo photodissociation:
O3 + hv O2 + 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 Cl radicals. These chlorine radicals react with ozone:
Cl+O3 O2+ClO (6)
The ClO formed is another reactive free radical, which can react with oxygen atoms.
ClO+O Cl+O2 (7)
O+O2 O3
So, reaction 4 and 6 are competing with each other to remove oxygen from the stratosphere. the
rate of reaction of ozone with Cl is over 1500 times greater than that of the one with O atoms.
Another important consideration is that the Cl atoms 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 tropospheric ozone, 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 ppbv in
polluted areas.
ozone–oxygen cycle
The ozone–oxygen cycle is the process by which ozone is continually regenerated
in Earth's stratosphere, converting ultraviolet radiation (UV) into heat. In 1930 Sydney
Chapman resolved the chemistry involved. The process is commonly called the Chapman
cycle by atmospheric scientists.

12. Ozone–oxygen cycle
1. Oxygen photolyzed to atomic oxygen
2. Oxygen and ozone continuously
interconverted. Solar UV breaks 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
of UV-B, UV- Cand above) into two oxygen atoms
O2 + ℎν(<242 nm) → 2O
 Each oxygen atom then quickly combines with an oxygen molecule to form an
ozone molecule:
O + O2 → O3

14. 2) The ozone–oxygen cycle:
 The ozone molecules formed by the reaction above absorb radiation having an appropriate
wavelength between UV-C and UV-B.
 The triatomic ozone molecule becomes diatomic molecular oxygen plus a free oxygen atom
O3 + ℎν(240–310 nm) → O2 + O
 The atomic oxygen produced quickly reacts with another oxygen molecule to reform ozone:
O + O2 + A → O3 + A
 where A denotes another molecule or atom, like N2 or O2 which 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 extra kinetic energy.
 These two reactions form the ozone–oxygen cycle, in which the chemical energy released when O
and O2 combine 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. O3 + O → 2 O2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O2
O3 + O → 2 O2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O2
O3 + O → 2 O2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O2
O3 + O → 2 O2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O2
O3 + O → 2 O2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O2
O3 + O → 2 O2
And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O2
Removal:
 if an oxygen atom and an ozone molecule meet, they recombine to form two oxygen
molecules:
O3 + O → 2 O2
 And if two oxygen atoms meet, they react to form one oxygen molecule:
2 O → O2
 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 cycle keeps 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-):