Acids are a class of chemical substances that, when dissolved in water, typically produce hydrogen ions (H⁺). Oxo acids, also known as oxy acids, are a type of acid that contain oxygen atoms, along with hydrogen and another element (often a nonmetal). The general structure of an oxo acid is HnXOm, where "X" where represents the halogen atom and n represents the number of oxygen atoms bonded to the halogen, "n" is the number of hydrogen atoms, and "m" is the number of oxygen atoms. The strength of an oxo acid depends on factors such as the number of oxygen atoms and the electronegativity of the central atom. oxo acids are versatile compounds with widespread applications in various fields, ranging from industry and agriculture to biology and medicine. Understanding their properties and reactions is crucial for advancing scientific knowledge and technology.

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OXO-ACIDS OF HALOGENS
&
THEIR SALTS
MOHAMMED FARHAN V
Dep. of Chemistry, PONDICHERRY UNIVERSITY
CHEM-211

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OXO-ACIDS OF HALOGENS
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 Hypohalous Acids HOX
 Halous Acids HXO2
 Halic Acids HXO3
 Perhalic Acids HXO4
All these structures are based on a tetrahedron. The sp3 hybrid orbitals
used for bonding form only weak σ bonds, because the s and p levels
differ appreciably in energy. The ions are stabilized by strong pπ – dπ
bonding between full 2p orbitals on oxygen with empty d orbitals on the
halogen atoms

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 Hypofluorous Acid
Why HOF is unstable?
Fluorine has very small size, high electronegativity and no d orbitals thus cannot form pπ-dπ
bonds. For a long time it was thought that F could not form any oxoacids, it is now known that HOF
can be made under special conditions. Therefore it forms only one oxoacid
• HOF is a colorless unstable gas
• It is a strong oxidizing agent and oxidizes H2O to H2O2 quite readily
• HOF is explosive at room temperature, forming HF and O2
2 HOF → 2 HF + O2
-40 °C
F2+ H2O HOF + HF
It was isolated in the pure form by passing F2 gas over ice at −40 °C
 Oxo-acids of Fluorine

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 Hypochlorous Acid
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 Chlorous Acid
• They are week acid, but they are good oxidizing agents especially in acidic solutions
• In Organic chemistry, HOCl coverts Alkenes to Chlorohydrins
• Sodium hypochlorite (NaClO) and Calcium hypochlorite (Ca(ClO)2) are ingredients in
many commercial bleaches, deodorants, disinfectants and sterilizing agent
HClO2 is made by treating berium chlorite with sulfuric acid, and filtering off the BaSO4
They can be prepared by shaking the halogen with freshly precipitated HgO in water
2HgO + H2O + 2Cl2 → HgO ∙ HgCl2 + 2HOCl
Ba(ClO2)2 + H2SO4 → 2HClO2 + BaSO4
• HClO2 is a powerful oxidizing agent, although its tendency to disproportionation
counteracts its oxidizing potential. It is a weak acid, but stronger than HOCl
Salts of HClO2 are called chlorites, and are made either from ClO2 and sodium hydroxide, or ClO2 and sodium peroxide
2ClO2 + 2NaOH → NaClO2 + NaClO3 + H2O 2ClO2 + Na2O2 → 2NaClO2 + O2
Chlorite Chlorate
Chlorites are used as bleaches
 Oxo-acids of Chlorine

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 Chloric Acid
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It can be prepared by the reaction of sulfuric acid with barium chlorate, the insoluble barium sulfate being
removed by precipitation
• Chlorates are much more soluble than bromates and iodates
• Solid chlorates, bromates and iodates should be handled with care
Ba(ClO3)2 + H2SO4 → 2HClO3 + BaSO4
Another method is the heating of hypochlorous acid, producing chloric acid and HCl
3HClO → HClO3 + 2HCl
Chlorates may be made in two ways
i. Passing Cl2 into a hot solution of NaOH
ii. Electrolysing hot chloride solutions that are vigorously stirred
• Chloric acid is a powerful oxidizing agent. Most organics and flammables will
deflagrate on contact
6NaOH + 3Cl2 NaClO3 + 5NaCl + 3H2O
2Cl- + 2H2O Cl2 + H2 + 2OH-
6NaOH + 3Cl2 NaClO3 + 5NaCl + 3H2O
80 °C
electrolyze
Uses,
• Chlorates are used to make fireworks and matches.
• Sodium chlorate is widely used as a powerful weedkiller.
• Solid sodium chlorate has been used by terrorists in making
bombs

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 Perchloric Acid
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Treating sodium perchlorate solution with hydrochloric acid (HCl) produces perchloric acid by precipitating solid sodium chloride.
It can also be prepared in laboratories by treating barium perchlorate (Ba(ClO4)2) with sulphuric acid (H2SO4)
which precipitates barium sulphate (BaSO4) and leaves perchloric acid
NaClO4 + HCl → NaCl + HClO4
Ba(ClO4)2 + H2SO4 → 2HClO4 + BaSO4
Uses,
• NH4ClO4 is a white solid and was formerly used as a blasting compound
in mining. It is now used in the booster rockets in the Challenger Space
Shuttle to oxidize the fuel (Al powder). NH4ClO4 will absorb sufficient
ammonia to liquefy itself.
• KClO4 is used in fireworks and flares.
• MgClO4 is used as the electrolyte in so-called ‘dry batteries’. It is very
hygroscopic, and is a very effective desiccant called ‘anhydrone’.
• HClO4 is a colorless compound and stronger acid than sulfuric acid, nitric
acid and hydrochloric acid
• It is a powerful oxidizer

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 Oxo-acids of Bromine
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 Bromic Acid
 Perbromic Acid
It is weak and unstable acid, They also called "Bromanol" or "Hydroxidobromine"
HOBr is used as a bleach, an oxidizer, a deodorant, and a disinfectant, due to its ability to kill the cells of
many pathogens.
hypobromite salts are unstable and undergo a slow disproportionation reaction to yield the respective
bromate and bromide salts.
Its chemical and physical properties are similar to those of other hypohalites
It is only exist in aqueous solution, It is a colorless solution that turns yellow at room temperature as it decomposes
to bromine
Bromic acid and bromates are powerful oxidizing agents
Ba(BrO3)2 + H2SO4 → 2 HBrO3 + BaSO4
Perbromic acid is unstable and cannot be formed by displacement of chlorine from perchloric acid,
as periodic acid is prepared; it can only be made by protonation of the perbromate ion.
It decomposes rapidly on standing to bromic acid and oxygen. It reacts with bases to form perbromate salts.
 Hypobromous Acid

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 Oxo-acids of Iodine
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Hypoiodous acid is a greenish yellow solution with chemical formula HOI.
Iodine reacts with cold and dilute sodium hydroxide solution sodium hypoiodite is formed which undergoes hydrolysis to give
hypoiodous acid
HIO3 is soluble in water and also exists in a pure state.
Iodic acid can be obtained by oxidizing iodine with strong oxidizers like nitric acid, hydrogen
peroxide, chloric acid and chlorine.
 Hypoiodous Acid
 Iodic Acid
Uses,
• Used as a strong oxidizing agent
• Used in rocket fuels and as an insulator
• Used to eliminate chloramines from swimming pool water to avoid the build-up of eye irritants
2NaOH + I2 → NaIO + NaI + H2O Another ; NaOH + I2 → HOI + NaI
NaIO + H2O → NaOH + HOI
Uses,
• It is used in the salt industry to synthesize sodium and potassium iodate to increase the iodine content in the salt
• In analytical chemistry, it is used as a strong acid
• It may be used to standardize solutions of both weak and strong bases, using methyl red or methyl orange as the indicator.

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Hydration of HIO4 gives H5IO6 and dehydration of H5IO6 gives HIO4.
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 Periodic acid
It can exist in two forms
i. orthoperiodic acid (H5IO6)
ii. metaperiodic acid (HIO4)
Orthoperiodic acid
Metaperiodic acid
Periodic acid is a strong oxidizing agent, commonly used to oxidize glycols.
HIO4 is the highest oxoacid of iodine
Periodic acid was discovered by eminent scientists Heinrich Gustav Magnus
and C. F. Ammermüller in the year 1833
• Conjugate base is Periodate.
• It is used to separate ammonia (NH3) from hydroxy amino acids and produce acetaldehyde and
higher aldehydes.

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STRENGHT OF THE OXO-ACID
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• HClO4 is an extremely strong acid, whilst HOCl is a very weak acid
• Note that the acidic nature of oxoacids is due to the highly polar nature of
the bond between hydrogen and oxygen
HClO4 >HBrO4 >HIO4
As the electronegativity of halogen decreases from F to I the polarity of the H—O bond also decreases as oxygen
can attract electron density from both H and halogen resulting the decrease in ionization. Therefore higher
the electronegativity of the halogen atom is higher acid strength.
Acidic strengh of Perhalic acids
Acidic strenght of Oxo-acids of Halogen with same oxidation number
decreases as we move down the group
Acidic strenght of Hypohalous Acids
HOF >HOCl >HOBr >HOI
But in the case of halic acids of different halogens the acidic character should increase
in the order;

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 Thermal Stability
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Thermal stability of both oxo-acid and their aions depend upon the Oxidation state, when the
oxidation state increases with increasing thermal stability
HClO < HClO2 < HClO3 < HClO4
Cl—O– > ClO2
− > ClO3
− > ClO4
−
 Oxidizing Power
As the stability of the anion increased from ClO– to ClO4
− the oxidizing power would decrease from
ClO– to ClO4
− .When the Oxidation state increases with decreases the Oxidation power.

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