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Ozone

2007 Schools Wikipedia Selection. Related subjects: Chemical compounds;
Climate and the Weather

                           Ozone

                          General
   Systematic name         Trioxygen
   Molecular formula       O[3]
   Molar mass              47.998 g/mol
   Appearance              bluish colored gas
   CAS number              [10028-15-6]
                        Properties
   Density and phase       2.144 g/l (0 °C), gas
   Solubility in water     0.105 g/100 ml (0 °C)
   Melting point           80.7 K, −192.5 °C
   Boiling point           161.3 K, −111.9 °C
                    Thermodynamic data
   Standard enthalpy of
   formation Δ[f]H°[solid] +142.3 kJ/mol
   Standard molar entropy
   S°[solid]               237.7 J.K^−1.mol^−1
                          Hazards
   EU classification       not listed
   NFPA 704
                  Supplementary data page
   Structure and
   properties              n, ε[r], etc.
   Thermodynamic
   data                    Phase behaviour
                           Solid, liquid, gas
   Spectral data           UV, IR, NMR, MS
   Regulatory data         Flash point,
                           RTECS number, etc.
     Except where noted otherwise, data are given for
   materials in their standard state (at 25 °C, 100 kPa)
   Infobox disclaimer and references

   Ozone (O[3]) is a triatomic molecule, consisting of three oxygen atoms.
   It is an allotrope of oxygen that is much less stable than the diatomic
   species O[2]. It is present in low concentrations throughout the
   Earth's atmosphere. It has many industrial and consumer applications as
   well as being used in ozone therapy.

   Ozone, the first allotrope of a chemical element to be described by
   science, was discovered by Christian Friedrich Schönbein in 1840, who
   named it after the Greek word for smell (ozein), from the peculiar
   odour in lightning storms. The odour from a lightning strike is from
   electrons freed during the rapid chemical changes, not the ozone
   itself.

Physical properties

   Undiluted ozone is a pale blue gas at standard temperature and
   pressure; it forms a dark blue liquid below −112 °C and a violet-black
   solid below −193 °C . At concentrations found in the atmosphere it is
   colorless . The concentration above which it can be smelt ( odour
   threshold) is between 0.0076 and 0.036 ppm.

Chemistry

   Ozone is a powerful oxidizing agent. It is also unstable at high
   concentrations, decaying to ordinary diatomic oxygen:

          2 O[3] → 3 O[2].

   This reaction proceeds more rapidly with increasing temperature and
   decreasing pressure. Ozone will oxidize metals (except gold, platinum,
   and iridium) to oxides of the metals in their highest oxidation state:

          2 Cu^2+ + 2 H^+ + O[3] → 2 Cu^3+ + H[2]O + O[2]

   Ozone converts oxides to peroxides:

          SO[2] + O[3] → SO[3] + O[2]

   It also increases the oxidation number of oxides:

          NO + O[3] → NO[2] + O[2]

   The above reaction is accompanied by chemiluminescence. The NO[2] can
   be further oxidized:

          NO[2] + O[3] → NO[3] + O[2]

   The NO[3] formed can react with NO[2] to form N[2]O[5]:

          NO[2] + NO[3] → N[2]O[5]

   Ozone reacts with carbon to form carbon dioxide, even at room
   temperature:

          C + 2 O[3] → CO[2] + 2 O[2]

   Ozone does not react with ammonium salts but it reacts with ammonia to
   form ammonium nitrate:

          2 NH[3] + 4 O[3] → NH[4]NO[3] + 4 O[2] + H[2]O

   Ozone reacts with sulfides to make sulfates:

          PbS + 4 O[3] → PbSO[4] + 4 O[2]

   Sulfuric acid can be produced from ozone, either starting from
   elemental sulfur or from sulfur dioxide:

          S + H[2]O + O[3] → H[2]SO[4]
          3 SO[2] + 3 H[2]O + O[3] → 3 H[2]SO[4]

   All three atoms of ozone may also react, as in the reaction with
   tin(II) chloride and hydrochloric acid:

          3 SnCl[2] + 6 HCl + O[3] → 3 SnCl[4] + 3 H[2]O

   In the gas phase, ozone reacts with hydrogen sulfide to form sulfur
   dioxide:

          H[2]S + O[3] → SO[2] + H[2]O

   In an aqueous solution, however, two competing simultaneous reactions
   occur, one to produce elemental sulfur, and one to produce sulfuric
   acid:

          H[2]S + O[3] → S + O[2] + H[2]O
          3 H[2]S + 4 O[3] → 3 H[2]SO[4]

   Iodine perchlorate can be made by treating iodine dissolved in cold
   anhydrous perchloric acid with ozone:

          I[2] + 6 HClO[4] + O[3] → 2 I(ClO[4])[3] + 3 H[2]O

   Solid nitryl perchlorate can be made from NO[2], ClO[2], and O[3]
   gases:

          2 NO[2] + 2 ClO[2] 2 O[3] → 2 NO[2]ClO[4] + O[2]

   Ozone can be used for combustion reactions and combusting gases in
   ozone provides higher temperatures than combusting in dioxygen (O[2]).
   Following is a reaction for the combustion of carbon subnitride:

          3 C[4]N[2] + 4 O[3] → 12 CO + 3 N[2]

   Ozone can react at cryogenic temperatures. At 77 K (-196 °C), atomic
   hydrogen reacts with liquid ozone to form a hydrogen superoxide
   radical, which dimerizes:

          H + O[3] → HO[2] + O
          2 HO[2] → H[2]O[4]

   Ozonides can be formed, which contain the ozonide anion, O[3]^-. These
   compounds are explosive and must be stored at cryogenic temperatures.
   Ozonides for all the alkali metals are known. KO[3], RbO[3], and CsO[3]
   can be prepared from their respective superoxides:

          KO[2] + O[3] → KO[3] + O[2]

   Although KO[3] can be formed as above, it can also be formed from
   potassium hydroxide and ozone:

          2 KOH + 5 O[3] → 2 KO[3] + 5 O[2] + H[2]O

   NaO[3] and LiO[3] must be prepared by action of CsO[3] in liquid NH[3]
   on an ion exchange resin containing Na^+ or Li^+ ions:

          CsO[3] + Na^+ → Cs^+ + NaO[3]

   Treatment with ozone of calcium dissolved in ammonia leads to ammonium
   ozonide and not calcium ozonide:

          3 Ca + 10 NH[3] + 6 O[3] → Ca•6NH[3] + Ca(OH)[2] + Ca(NO[3])[2]
          + 2 NH[4]O[3] + 2 O[2] + H[2]

   Ozone can be used to remove manganese from the water, forming a
   precipitate which can be filtered:

          2 Mn^2+ + 2 O[3] + 4 H[2]O → 2 MnO(OH)[2 (s)] + 2 O[2] + 4 H^+

   Ozone will also turn cyanides to the one thousand times less toxic
   cyanates:

          CN^- + O[3] → CNO^- + O[2]

   Finally, ozone will also completely decompose urea:

          (NH[2])[2]CO + O[3] → N[2] + CO[2] + 2 H[2]O

Ozone in Earth's atmosphere

   Concentration of ozone as measured by the Nimbus-7 satellite.
   Enlarge
   Concentration of ozone as measured by the Nimbus-7 satellite.

   The standard way to express total ozone amounts (the amount of ozone in
   a vertical column) in the atmosphere is by using Dobson units.
   Concentrations at a point are measured in parts per billion (ppb) or in
   μg/m³.

Ozone layer

   Total ozone concentration in June 2000 as measured by EP-TOMS satellite
   instrument.
   Enlarge
   Total ozone concentration in June 2000 as measured by EP-TOMS satellite
   instrument.

   The highest levels of ozone in the atmosphere are in the stratosphere,
   in a region also known as the ozone layer between about 10 km and 50 km
   above the surface. Here it filters out the shorter wavelengths (less
   than 320 nm) of ultraviolet light (270 to 400 nm) from the Sun that
   would be harmful to most forms of life in large doses. These same
   wavelengths are also responsible for the production of vitamin D, which
   is essential for human health. Ozone in the stratosphere is mostly
   produced from ultraviolet rays reacting with oxygen:

          O[2] + (radiation < 240 nm) → 2 O

          O + O[2] → O[3]

   It is destroyed by the reaction with atomic oxygen:

          O[3] + O → 2 O[2]

   (See Ozone-oxygen cycle for more detail.)

   The latter reaction is catalysed by the presence of certain free
   radicals, of which the most important are hydroxyl (OH), nitric oxide
   (NO) and atomic chlorine (Cl) and bromine (Br). In recent decades the
   amount of ozone in the stratosphere has been declining mostly due to
   emissions of CFCs and similar chlorinated and brominated organic
   molecules, which have increased the concentration of ozone-depleting
   catalysts above the natural background. See ozone depletion for more
   information. For more information on stratospheric ozone see Seinfeld
   and Pandis (1999).

Low level ozone

   Low level ozone (or tropospheric ozone) is regarded as a pollutant by
   the World Health Organisation. It is not emitted directly by car
   engines or by industrial operations. It is formed by the reaction of
   sunlight on air containing hydrocarbons and nitrogen oxides that to
   form ozone directly at the source of the pollution or many kilometers
   down wind. For more details of the complex chemical reactions that
   produce low level ozone see tropospheric ozone or Seinfled and Pandis
   (1998).

   Ozone reacts directly with some hydrocarbons such as aldehydes and thus
   begins their removal from the air, but the products are themselves key
   components of smog. Ozone photolysis by UV light leads to production of
   the hydroxyl radical and this plays a part in the removal of
   hydrocarbons from the air, but is also the first step in the creation
   of components of smog such as peroxyacyl nitrates which can be powerful
   eye irritants. The atmospheric lifetime of tropospheric ozone is about
   22 days and its main removal mechanisms are being deposited to the
   ground, the above mentioned reaction giving OH, and by reactions with
   OH and the peroxy radical HO[2]· (Stevenson et al, 2006) .

   As well as having an impact on human health (see below) there is also
   evidence of significant reduction in agricultural yields due to
   increased ground-level ozone and pollution which interferes with
   photosynthesis and stunts overall growth of some plant species.

Ozone as a greenhouse gas

   Although ozone was present at ground level before the industrial
   revolution, peak concentrations are far higher than the pre-industrial
   levels and even background concentrations well away from sources of
   pollution are substantially higher. This increase in ozone is of
   further concern as ozone present in the upper troposphere acts as a
   greenhouse gas, absorbing some of the infrared energy emitted by the
   earth. Quantifying the greenhouse gas potency of ozone is difficult as
   it is not present in uniform concentrations across the globe. However,
   the most recent scientific review on the climate change (the IPCC Third
   Assessment Report) suggests that the radiative forcing of tropospheric
   ozone is about 25% that of carbon dioxide.

Ozone and health

Ozone in air pollution

   There is a great deal of evidence to show that high concentrations
   (ppm) of ozone, created by high concentrations of pollution and
   daylight UV rays at the earth's surface, can harm lung function and
   irritate the respiratory system . There has also been shown to be a
   connection between increased ozone caused by thunderstorms and hospital
   admissions of asthma sufferers . Air quality guidelines such as those
   from the World Health Organization are based on detailed studies of
   what levels can cause measurable health effects.

Physiology of ozone

   Ozone, along with reactive forms of oxygen such as superoxide, singlet
   oxygen (see oxygen), hydrogen peroxide, and hypochlorite ions, is
   naturally produced by white blood cells and other biological systems
   (such as the roots of marigolds) as a means of destroying foreign
   bodies. Ozone reacts directly with organic double bonds. Also, when
   ozone breaks down to dioxygen it gives rise to oxygen free radicals,
   which are highly reactive and capable of damaging many organic
   molecules. Ozone has been found to convert cholesterol in the blood
   stream to plaque (which causes hardening and narrowing of arteries).
   Moreover, it is believed that the powerful oxidizing properties of
   ozone may be a contributing factor of inflammation. The
   cause-and-effect relationship of how the ozone is created in the body
   and what it does is still under consideration and still subject to
   various interpretations, since other body chemical processes can
   trigger some of the same reactions. A team headed by Dr. Paul Wentworth
   Jr. of the Department of Chemistry at the Scripps Research Institute
   has shown evidence linking the antibody-catalyzed water-oxidation
   pathway of the human immune response to the production of ozone. In
   this system, ozone is produced by antibody-catalyzed production of
   trioxidane from water and neutrophil-produced singlet oxygen. . See
   also trioxidane for more on this biological ozone-producing reaction.

   Ozone has also been proven to form specific, cholesterol-derived
   metabolites that are thought to facilitate the build-up and
   pathogenesis of atherosclerotic plaques (A form of heart disease).
   These metabolites have been confirmed as naturally occurring in human
   atherosclerotic arteries and are categorized into a class of
   secosterols termed “Atheronals”, generated by ozonolysis of
   cholesterol's double bond to form a 5,6 secosterol as well as a
   secondary condensation product via aldolization. Volume: Number: Page:
   23 DOI:

Safety

Artificial production

   Ozone may be formed from O[2] by electrical discharges and by action of
   high energy electromagnetic radiation. Certain electrical equipment
   generate significant levels of ozone. This is especially true of
   devices using high voltages, such as laser printers, photocopiers, and
   arc welders. Electric motors using brushes can generate ozone from
   repeated sparking inside the unit. Large motors, such as those used by
   elevators or hydraulic pumps, will generate more ozone than smaller
   motors.

Industrial production

   Ozone used in industry is measured in ppm or mg/L ( OSHA exposure
   limits for example), and percent by mass or weight. Industrially, ozone
   is produced with short wavelength ultraviolet radiation from a mercury
   vapor lamp or the application of a high voltage electrical field in a
   process called cold or corona discharge. The cold discharge apparatus
   consists of two metal plates separated by an air gap and a high
   dielectric strength electrical insulator such as borosilicate glass or
   mica. A high voltage alternating current is applied to the plates and
   the ozone is formed in the air gap when O[2] molecules disassociate and
   recombine into O[3]. A faint corona may be present in the air gap, but
   the voltage is maintained below that which would cause punch-through of
   the insulator with subsequent arcing and plasma formation.

Laboratory production

   In the laboratory ozone can be produced by electrolysis using a 9 volt
   battery, a pencil graphite rod cathode, a platinum wire anode and a 3M
   sulfuric acid electrolyte. The half cell reactions taking place are:

          3 H[2]O → O[3] + 6 H^+ + 6 e^− ΔE^o = − 1.53 V
          6 H^+ + 6 e^− → 3 H[2] ΔE^o = 0 V
          2 H[2]O → O[2] + 4 H^+ + 4 e^− ΔE^o = −1. 23 V

   So that in the net reaction three equivalents of water are converted
   into one equivalent of ozone and three equivalents of hydrogen. Oxygen
   formation is a competing reaction.

Applications

Industrial applications

   Ozone can be used for bleaching substances and for killing bacteria.
   Many municipal drinking water systems kill bacteria with ozone instead
   of the more common chlorine. Ozone does not form organochlorine
   compounds, but it also does not remain in the water after treatment, so
   some systems introduce a small amount of chlorine to prevent bacterial
   growth in the pipes, or may use chlorine intermittently, based on
   results of periodic testing. Where electrical power is abundant, ozone
   is a cost-effective method of treating water, as it is produced on
   demand and does not require transportation and storage of hazardous
   chemicals. Once it has decayed, it leaves no taste or odour in drinking
   water. Low level of Ozone is helpful to purify air inside the house.
   Eliminate mildew and mold build up.

   Industrially, ozone or ozonated water is used to
     * disinfect water before it is bottled;
     * deodorize air and objects, such as after a fire;
     * kill bacteria on food or on contact surfaces;
     * scrub yeast and mold spores from the air in food processing plants;
     * wash fresh fruits and vegetables to kill yeast, mold and bacteria;
     * chemically attack contaminants in water (iron, arsenic, hydrogen
       sulfide, nitrites, and complex organics lumped together as
       "colour");
     * provide an aid to flocculation (agglomeration of molecules, which
       aids in filtration, where the iron and arsenic are removed);
     * clean and bleach fabrics (the latter use is patented);
     * assist in processing plastics to allow adhesion of inks;
     * age rubber samples to determine the useful life of a batch of
       rubber;
     * in surface water treatment plants to eradicate water borne
       parasites such as Giardia and Cryptosporidium. This process is
       known as ozonation.

   Ozone is a reagent in many organic reactions in the laboratory and in
   industry. Ozonolysis is the cleavage of an alkene to carbonyl
   compounds.

   Many hospitals in the U.S. and around the world use large ozone
   generators to decontaminate operating rooms between surgeries. The
   rooms are cleaned and then sealed airtight before being filled with
   ozone which effectively kills or neutralizes all remaining bacteria.

Consumer applications

   Ozone machines, with or without ionization, are currently used to
   sanitize (high ozone output) and deodorize non-inhabited rooms,
   ductwork, vehicles, boats, woodsheds, and buildings.

   Some models of air purifiers that also emit low levels of ozone have
   been sold in the US. These type of air purifiers claim to imitate
   nature's "filterless" air purifying mechanisms and claim to "sanitize"
   the air and/or household surfaces. The government successfully sued one
   company in 1995, ordering them to stop repeating health claims without
   supporting scientific studies.

   Ozonated water is used to launder clothes, sanitize food, drinking
   water, and surfaces in the home. According to the FDA, it is "amending
   the food additive regulations to provide for the safe use of ozone in
   gaseous and aqueous phases as an antimicrobial agent on food, including
   meat and poultry." Ironically, while ozone is considered an atmospheric
   pollutant, pollution and smog by the US government, it can actually
   reduce pollutants like pesticides in fruits and vegetables.

   Ozone is used in spas or hot tubs with reduced levels of Chlorine or
   Bromine for keeping the water free of bacteria. As it does not remain
   in the water after treatment, it is ineffective at preventing bather
   cross-contamination, and must be used in conjuction with another
   sanitizer. Ozone gas is created by an ultraviolet light bulb or corona
   discharge chip and injected into the plumbing system.

   Ozone is also widely used in treatment of water in aquaria and fish
   ponds. Its use can minimise bacterial growth control parasites and
   removes or reduce "yellowing" of the water. As the Ozone rapidly
   decomposes, at correctly controlled levels the application has no
   effect on the fish.

Pharmaceutical applications

   Ozone has a number of medical uses. It can be used to affect the body's
   antioxidant-prooxidant balance, since the body usually reacts to its
   presence by producing antioxidant enzymes. Ozone therapy has blossomed
   into a thriving field of alternative medicine, with a host of claimed
   applications far above and beyond what has actually been verified by
   studies .

   Retrieved from " http://en.wikipedia.org/wiki/Ozone"
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   with only minor checks and changes (see www.wikipedia.org for details
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