This document discusses various oxyacids of sulfur. It begins by defining oxyacids of sulfur as compounds containing sulfur, hydrogen and oxygen. It then lists and describes 9 common oxyacids of sulfur - sulphurous acid, sulphuric acid, peroxomonosulphuric acid, peroxodisulphuric acid, thiosulphuric acid, dithionous acid, dithionic acid, polythionic acid and pyrosulphuric acid. The document focuses on describing the structure, methods of preparation, properties and uses of the most important oxyacids - sulphurous acid and sulphuric acid.

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OXYACIDS OF SULPHUR
INORGANIC CHEMISTRY ASSIGNMENT
2/15/2017
RABIA AZIZ (BS-III CHEMISTRY)

2. OXYACIDS OF SULPHUR
RABIA AZIZ BS-III CHEMISTRY Page 2
Contents:
ABSTRACT..............................................................................................................................1
INTRODUCTION...................................................................................................................1
1. SULPHUROUS ACID.......................................................................................................3
2. SULPHURIC ACID...........................................................................................................4
3. PEROXOMONOSULPHURIC ACID...............................................................................8
4. PEROXODISULPHURIC ACID.......................................................................................9
5. THIOSULPHURIC ACID.................................................................................................10
6. DITHIONOUS ACID........................................................................................................12
7. DITHIONIC ACID............................................................................................................12
8. POLYTHIONIC ACID......................................................................................................14
9. PYROSULPHURIC ACID................................................................................................15
REFERENCE...........................................................................................................................18
CONCLUSION........................................................................................................................18

3. OXYACIDS OF SULPHUR
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ABTRACT:
Oxyacids of sulphur are sulphur, hydrogen and oxygen containing compounds. Oxyacids of
sulphur are sulphurous acid, sulphuric acid, peroxomonsulphuric acid, peroxodisulphuric acid,
thiosulphuric acid, dithionous acid, dithionic acid, polythionic acid and pyrosulphuric acid.
Sulphuric acid is found as a free acid, but other acids are mostly unstable and convert into their
salts and ions.
Introduction:
Oxyacids of sulphur are chemical compounds that contain sulphur, hydrogen and oxygen.
Sulphur forms a number of oxyacids. Many of oxyacids of sulphur are not existed as free acids
and these are found as anions and salts. Some important oxyacids of sulphur are following:

4. OXYACIDS OF SULPHUR
RABIA AZIZ BS-III CHEMISTRY Page 4
Series of Oxyacid of Sulphur: Oxyacids of sulphur are divided in four series
according to the their structural similarities which are following:
1. Sulphurous acid series
2. Sulphuric acid series
3. Thionic acid series
4. Peroxo acid series
1. Sulphurous Acid Series:Under this series sulphurous acid, di or pyrosulphurous
acid and dithionous acid are grouped.
2. Sulphuric Acid Series:Sulphuric acid, thiosulphuric acid and di or pyrosulphuric
acid.
3. Thionic Acid Series:Dithionic and polythionic acid.
4. Peroxo Acid Series: Peroxo monosulphuric acid and peroxo disulphuric acid.
1. SULPHUROUS ACID (H2SO3):
Sulphurous acid is obtained by dissolving SO2 in water.
SO2 + H2O ==> H2SO3
A saturated solution at 3°C gives crystal of sulphurous acids having generally H2SO3.6H2O
formula.
Properties:
1. Action of Heating: When heated, various products are formed.
3H2SO3 → H2SO4 + H2S2O4 + H2O
H2S204 →H2SO4 + S
2. Reaction with Halogen: Sulphuric acid is formed as a final product.
H2SO4 + H2O + CL2 → H2SO4 + 2HCL
H2SO3 + H2O + I2 → H2SO4 + 2HI
3. Reducing Properties: It reduces ferric to ferrous and iodates to iodine.
2FeCL2 + H2SO3 + H2O → 2FeCL2 + H2SO4 + 2HCL
5H2SO3 + 2KIO3 → 2KHSO4 + 3H2SO4 + H20 +I

5. OXYACIDS OF SULPHUR
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4. Decolourization of KMnO4: It decolourises dilute mineral solution of
KMnO4.
2KMnO4 + 5H2SO3 → 2KHSO4 + 2MnSO4 + H2SO4 + 3H2O
5. Reaction with Alkali: Sulphites and bisulphites are the important salts of this
acid which are obtained.
NaOH + H2SO3 → NaHSO3 + H2O
NaHSO3 + NaOH → Na2SO3 + H2O
Sulphites are oxidised to sulphates in the presence of bromine water.
Na2SO3 + Br2 + H2O →Na2SO4 + 2HBr
Structure:
X-ray analysis of Na2SO3 crystals reveals that SO3 ion has a pyramidal structure with three
oxygen atoms in a triangular. Lone pair distort the tetrahedral structure to form pyramidal
structure.
USES:
(i) Sulphurous acid is a strong reducing agent.
(ii) The solution has bleaching properties.
2. SULPHURIC ACID:
Chemical formula: H2SO4, Molecular weight: 98.079 g/mol
Occurrence:

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Sulfuric acid is formed naturally by oxidation of sulfide minerals in rocks. Dilute sulfuric acid is
also formed in the atmosphere by oxidation of sulfur dioxide (from burning of fuels) in the
presence of moisture, eventually precipitating as 'acid rain'.
Structure of Sulphuric Acid:
Pure sulphuric acid is covalent, its molecule having an approximately tetrahedral structure
containing six-valent sulphur.
The sulfur atom is bound to two oxygen atoms through double bonds, and two hydroxyl groups
(OH) through single bonds. It is a diprotic acid, as it can release two protons.
Preparation:
Sulphuric acid is an important acid. It is obtained by two process (i) lead chamber process (ii)
contact process. Sulphur dioxide is obtained by chemical reactions which is oxidised to SO3. SO3
is dissolved in water to give H2SO4.
SO3 + H2O → H2SO4
CONTACT PROCESS:
By this process 100% pure sulphuric acid can be obtained. The process involves the catalytic
oxidation of SO2 to SO3 by atmosphere oxygen.
2SO2 + O2 ↔ 2SO3 + 23Kcal
SO3 + H2O → H2SO4

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Sulphuric acid absorbs more SO3 to give oleum. When calculated amount of water added,
sulphuric acid is obtained.
SO3 + H2SO4 → H2S2O7 oleum
H2S2O7 + H2O → 2H2SO4
LEAD –CHAMBER PROCESS:
In this process SO2 is oxidized by atmospheric oxygen in the presence of catalyst of oxides of
nitrogen. The SO3 so obtained is absorbed by water to get sulphuric acid.
2NO + O2 → 2NO2
NO2 + SO2 + H2O → H2SO4 (99%) + NO
Source of SO2:
Burning of sulphur: 2S + O2 → 2SO2

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Burning of pyrites: 4FeS2 + 11O2 → 2Fe2O3 + 8SO2
Source of oxides of Nitrogen: By heating KNO3 with sulphuric acid in the nitre oven.
KNO3 + H2SO4 → KHSO4 + HNO3
2HNO3 + 2SO2 → 2SO2 + H2O + NO + NO2
Plant:
1. Pyrite burner
2. Nitre pot
3. Dust catcher’s
4. Glover tower
5. Lead chamber
6. Gay lussac tower
7. Cooler
Properties:
Physical properties: H2SO4 is a colorless or slightly yellow viscous liquid with a
pungent odor. It has a density of 1.84 g/mL, boiling point of 337 °C, and melting point of 10 °C.
"Concentrated" sulfuric acid is 98% in water, and is the most stable form. Many other

9. OXYACIDS OF SULPHUR
RABIA AZIZ BS-III CHEMISTRY Page 9
concentrations, with different names, are available for various purposes. Battery acid is 29–32%,
chamber acid is 62-70%, and tower acid is 78-80%.
Chemical Properties: Sulphuric acid is a very strong, diprotic acid. It is hygroscopic
and readily absorbs moisture from air. It is a powerful oxidizing agent and reacts with many
metals at high temperatures. Concentrated H2SO4 is also a strong dehydrating agent. Addition of
water to concentrated sulphuric acid is a very exothermic reaction and can lead to explosions.
1. Dibasic Acid: It is strongly dibasic acid. It ionises into two ions.
H2SO4 → H+ + HSO4
-
HSO4
- →H+ + SO4
-
When acid reacts with alkali, two types of salts are produced.
NaOH + H2SO4 → NaHSO4 + H2O
NaHSO4 + NaOH → Na2SO4 + H2O
2. Dehydrating Agent: It has great affinity towards water. Thus it removes water
molecule when reacts with organic compound.
C12H22O11 + H2SO4 → 12C + 11H2O
(COOH)2 + H2SO4 → H20 + CO + CO2
3. As oxidizing Agent:
a. It reacts with non-metals like C,S and oxides them into CO2 and SO2.
C + 2H2SO4 → CO2 + 2SO2 + 2H2O
S+ 2H2SO4 → 3SO2 + 2H2O
b. Reaction with Metals: It reacts with metals to form salt.
Cu + 2H2SO4 → CuSO4 + SO2 + 2H2O
c. KI and KBr are oxidised to free iodine and free bromine.
2KI + 2H2SO4 → K2SO4 + 2H2O + I2 + SO2
4. Dehydrating Of Alcohol: When alcohol is heated with conc. H2SO4 at 170°C,
water is removed.
C2H5OH → C2H4 + H2O
Ethyl alcohol Ethylene
5. As Sulphonating Agent: It reacts with organic compounds and replaces one or
more hydrogen atoms from it by –SO3H group the process is called sulphonation.
CH4 + H2SO4 → CH3-SO3H + H2O
Methane sulphonic acid
Importance:

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Sulphuric acid is called ‘King of compound”. Its importance can be imagined by the saying that
progress and prosperity of a nation is determined by the consumption of H2SO4 that its industry
consumes.
Uses:
1. In manufacturing fertilizers such as super phosphate and ammonium nitrate.
2. In manufacturing Rayon and plastics.
3. In the manufacture of detergents.
4. It is used as dehydrating, nitrating and drying agent.
5. It uses in different industries, such as mineral processing, petroleum refining, wastewater
processing, etc.
6. It is also used in the production of cleaning agents, dyes, pigments, drugs, and explosives.
7. It is commonly used as the electrolyte in lead-acid batteries.
Health hazards: Concentrated H2SO4 is highly corrosive, and can severely damage tissues
upon contact. Being a strong acid, oxidizer, corrosive agent and dehydrating agent, it is more
dangerous than the other mineral acids. It causes severe chemical burns upon skin contact.
Contact with eyes can lead to permanent damage and blindness. Ingestion of the acid can even
lead to death.
3. PEROXOMONOSULPHURIC ACID:
Chemical formula: H2SO5
Peroxymonosulfuric acid, also known as persulfuric acid or Caro's acid, a strongly
oxidizing acid with the formula H2SO5 first described by Heinrich Caro in 1898.
Caro's acid is used in industrial organic syntheses (e.g. oxidation of ketones to lactones or
esters), it is used extensively for disinfecting and cleaning (e.g. metals), and has been applied
industrially as an oxidizing acidic leaching solution for the extraction of uranium from ore.
Its salts have wide variety of industrial uses. The potassium salt, potassium
peroxymonosulfate, is sold under the name Oxone for treating swimming pools.
Preparation:
(i) For laboratory use, small quantities of Caro's acid may be prepared by slowly adding
H2O2 to concentrated sulfuric acid contained in a inert container e.g., glass,
surrounded by an ice bath. The heat of dilution of the sulfuric acid causes strong
heating, which makes the acid more unstable, so temperature control is essential.

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The process results in a mixture of Caro's acid, H2SO4, H2O2 and water, the ratios
depending on the strength of the reagents, and their proportion.
H2O2 + H2SO4 → HOOSO2 + H2O
(ii) From Hydrolysis of Peroxodisulphuric acid (Marshall‘s acid):
H2S2O8 + H2O → H2SO5+ H2SO4
Properties:
Chemical
Caro's acid is among the strongest oxidizers known. It is unstable and is generally prepared
within a few days of use. It is highly explosive, especially in mixtures with organic matter.
Physical
Caro's acid solutions are clear, colorless and are very viscous and have a oily consistency.
The density is in the range 1.7 - 1.8 grams per milliliter.
Structure: Based on its synthesis from H2O2 or HSO3
4. PEROXODISULPHURIC ACID:
Chemical formula: H2S2O8
Preparation:
(i) The acid is prepared by the reaction of chlorosulfuric acid with hydrogen
peroxide:
2ClSO3H + H2O2 → H2S2O8 + 2 HCl
(ii) By electrolysis of 50% H2SO4 at low temperature:
At cathode:
H+ + e- → H
H + H → H2

12. OXYACIDS OF SULPHUR
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At anode:
2HSO4
- - 2e- → H2S2O8
Properties:
(i) It is a colourless crystalline solid having M.P 338K.
(ii) It undergoes hydrolysis giving Caro’s acid.
H2S2O8 + H2O → H2SO5 + H2SO4
(iii) Many metals such as Zn etc. Dissolve forming their sulphates without evolution
of any gas.
K2S2O8 + Zn → K2SO4 + ZnSO4
(iv) Its salt potassium peroxosulphate, K2S2O8 onheating evolves sulphur trioxide and
oxygen whereas the solution of the salt gives only oxygen on heating.
2K2S2O8 → 2K2SO4 + 2SO3 + O2
2K2S2O8 + 2H2O → 2K2SO4 + 2H2SO4 + O2
(v) Amphoteric metals, Cr, As, etc., form their oxy-acids.
3K2S2O6 + Cr + 4H2O → 3K2SO4 + H2CrO4 + 3H2SO4
(vi) Peroxodisulphate ion is one of the most powerful and useful oxidizing agents.
S2O8
2- + 2e- ↔ 2SO4
2- (E° = 2.01 volt)
It liberates iodine from potassium iodide, oxidizes Cr3+ to Cr2O7
2-, Fe2+ to Fe3+,
Mn2+ to MnO4
- etc.
K2S2O8 + 2KI → 2K2SO4 + I2
K2S2O8 + 2FeSO4 → Fe2(SO4)3 + K2SO4
5K2S2O8 + 2MnSO4 + 8H2O → 2KMnO4 + 4K2SO4 + 8H2SO4
Structure:
X-ray studies show that peroxodisulphate ion, the structure –O3S-O-O-SO3
- with
approximately tetrahedral angles about each sulphur atom. Also as the acid is prepared from
H2O2 and CISO3H reacting in the molecular ratio 1:2, the structure is represented as below:
5. THIOSULPHURIC ACID:
Chemical formula: H2S2O3
Preparation:
(i) By reaction of Sulphur trioxide with Hydrogen sulphide in the presence of ether.
SO3 + H2S → H2S2O3

13. OXYACIDS OF SULPHUR
RABIA AZIZ BS-III CHEMISTRY Page 13
(ii) ClSO3H + H2S → H2S2O3 + HCl
Properties:
(i) Free thiosulphuric acid is unstable and decomposes into sulphur as soon as it is
liberated from its salts solution by adding an acid.
H2S2O3 → SO2 + S + H2O
Thus its reactions are manily due to S2O3
2-, thiosulphate ion.
(ii) The thiosulphate ion, S2O3
2- behaves as a reducing agent of moderate strength.
2S2O3
2- → S4O6
2- + 2e-
Structure:
6. DITHIONOUS ACID:
Chemical formula: H2S2O4
It is unstable in pure form, but its salts, known as dithionites, are stable.
Preparation:
By reducing sulphurous acid containing sulphites with amalgamated Zn or Zinc dust:
2S2O4
2- + H2O → S2O3
2- + 2HSO3
-
Properties: Solution of dithionous acid and of its salts such as dithionites are powerful
reducing agents. For reducing purpose. Sodium dithionite is ordinarily employed. Sodium
dithionite is prepared by reducing sodium bisulphite solution with zinc dust and separated by
removing excess sulphite by precipitation with Ca(OH)2.
Structure:

14. OXYACIDS OF SULPHUR
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Uses:
(i) Sodium dithionite is a white powder used as a reductant and a bleaching agent.
(ii) It is also used to reduce the nitro group to an amino group in organic reactions.
7. DITHIONIC ACID:
Chemical formula: H2S2O6,
Preparation:
(i) Dithionic acid and its salts are best prepared by oxidation of SO2 or sulphite
solutions. This can be done electrically or by chemical oxidizing agent such as
Mn(IV) oxide, permanganate ion, iron(III) hydroxide.
(ii) Laboratory preparation involves treatment of aqueous suspension of Mn(IV)
dioxide with SO2 below 283K to form Mn(II) sulphate and dithionate in solution.
Removal of manganese and sulphate ions is done by adding Ba(OH);
BaS2O6.2H2O is then crysatllized.
2MnO2 + 3SO2 → MnS2O6 + MnSO4
MnO2 + 2SO3
2- +4H+ → Mn2+ + S2O6
2- +2H2O
MnSO4 + Ba(OH)2 → BaSO4 + Mn(OH)2
MnS2O6 + Ba(OH)2 → BaS2O6 + Mn(OH)2
On treating the aqueous solutions of this salt with H2SO4, free acid is obtained.
Properties:
Diththionic acid is moderately a strong and stable bibasic acid which decomposesd slowly in
concentrated solutions and on warming. Dithionates are stable to oxidizing agents and mild
reducing agents, but on heating in acid solution they give both H2SO4 and H2SO3.
H2S2O6 + H2O → H2SO4 + H2SO3
Structure:

15. OXYACIDS OF SULPHUR
RABIA AZIZ BS-III CHEMISTRY Page 15
8. POLYTHIONIC ACID:
Polythionic acid is an oxoacid which has a straight chain of sulfur atoms and has the
chemical formula H2SnO6 (n > 2). Trithionic acid (H2S3O6), tetrathionic acid (H2S4O6) are
simple examples. The compounds of n < 80 are expected to exist, and those of n < 20 have
already been synthesized. Their salts are called polythionates. Dithionic acid (H2S2O6) does
not belong to the polythionic acids due to strongly different properties.
Occurrence:
Polythionic acids are often found in crater lakes. There are various kinds of ions containing
sulfur atoms derived by hydrogen sulfide and they make the strongly acidic conditions. It is
observed that polythionates in crater lakes are drastically decreased before an eruption
occurs. The phenomenon may be useful to predict volcanic activity.
Preparation:
(i) By passing hydrogen sulphide through saturated aqueous solution of sulphur dioxide
till its smell disappears and milky solution, called Wackenroder’s liquid or solution is
produced. This solution contains a mixture of polythionic acids and free sulphur
along with H2S2O3, H2SO4 etc. The various reactions are:
H2S + H2SO3 → H2S2O2 + H2O
H2SO3 + 2H2S → 3H2O + 3S
At pH=0.5, the main reaction products are H2S4O6 and H2S6O6.
H2S2O2 + 2H2SO3 → H2S4O6 + H2O
H2S2O2 + 2H2S2O3 → H2S6O6 + 2H2O
At pH= 7, the main product is H2S3O6.
H2S2O2 + 3H2SO3 → H2S2O3 + H2S3O6 + 2H2O
In less acidic solutions, H2S2O6 decomposes giving a mixture of lower polythionic acids.
From the mixture of polythionic acids, each acid is isolated on the basis of difference in
solubilities of their potassium salts. The order of their solubility is

16. OXYACIDS OF SULPHUR
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K2S3O6 > K2S6O6 > K2S4O6 > K2S5O6
(ii) Anhydrous polythionic acids can be formed in diethyl ether solution by the following
three general ways:
HSnSO3H + SO3 → H2Sn+2O6 (n = 1, 2 … 8)
H2Sn + 2SO3 → H2Sn+2O6 (n = 1, 2 … 8)
2HSnSO3H + I2 → H2S2n+2O6 + 2HI (n = 1, 2 … 6)
(iii) By Hydrolysis of Sulphur monochloride:
S2Cl2 + 3H2O → H2SO3 + H2S + 2HCl
3H2SO3 + H2S → H2S4O6 + 3H2O
6H2SO3 + 2H2S → H2S3O6 + H2S5O6 + 6H2O
9H2SO3 + 3H2S → H2S2O6 + 2HS5O6 + 9H2O
Properties:
Physical Properties:
(i) Polythionic acids with a small number of sulfur atoms in the chain (x = 3 - 6) are the
most stable.
(ii) Polythionic acids are stable only in aqueous solutions, and are rapidly destroyed at
higher concentrations with the release of sulfur, sulfur dioxide and - sometimes -
sulfuric acid.
(iii) Polythionate ions are significantly more stable than the corresponding acids.
Chemcial Properties:
(i) Under the action of oxidants (potassium permanganate, potassium dichromate)
polythionic acids and their salts are oxidized to sulfate, and the interaction with strong
reducing agents (amalgam of sodium) converts them into sulfites and dithionites.
Structure:

17. OXYACIDS OF SULPHUR
RABIA AZIZ BS-III CHEMISTRY Page 17
9.PYROSULPHYRIC ACID:
Chemical formula: H2S2O7, Molar mass: 178.13 g/mol, Melting-point: 36° C
It is also known as Oleum (fuming sulphuric acid) / disulfuric acid.
Preparation:
(i) It is obtained is obtained by dissolving sulphuric trioxide in concentrated
sulphuric acid.
H2SO4 + SO3 → H2S2O7
(ii) Alkali metal pyrosulphate can be obtained by heating alkali bisulphite.
2NaHSO4 → Na2S2O7 + H2O
Properties:
(i) It is a viscous brownish liquid, fumes in air and gradually loses sulphuric trioxide.
Thus it changes into ordinary sulphuric acid on warming.
H2S2O7 → H2SO4 + SO3
(ii) Pyrosulphuric acid gives sulphuric acid when water is added into it.
H2S2O7 + H2O → 2H2SO4
(iii) It is an excellent sulphonating agent used in organic chemistry.
(iv) It is a much weaker acid than sulfuric acid.
(v) It readily reacts with bases to form salts called pyrosulfates, such as sodium and
potassium pyrosulfates.
Structure:
Pyrosulfuric acid can be considered as an anhydride of sulfuric acid (H2SO4), since its
structure is the same as one would get by combining two molecules of sulfuric acid, followed
by dehydration of one molecule of water.

18. OXYACIDS OF SULPHUR
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Uses:
(i) Its main uses are in the manufacture of explosives and dyes.
(ii) It is also used widely as a sulfating agent and in petroleum refining.
(iii) It is also commonly used as a convenient intermediate or form of sulfuric acid for
storage and transportation, due to its less corrosive nature. It can be diluted in water
to readily give sulfuric acid of the desired concentration.
CONCLUSION:
Oxyacids of sulphur are compounds of sulphur with oxygen and hydrogen. Sulphurous acid does
not exist as free acid; it is diprotic and strong reducing agent. Sulphuric acid is stable, diprotic
and dehydrating agent. Thiosulphuric acid does not exist as free acid but its salts, all are stable
reducing agent. Solution of dithionous acid and of its salts such as dithionites is powerful
reducing agents. Peroxomonosulphuric acid is stable and crystalline solid. Dithionic acid is
moderately stable but its salts are quite stable. Pyrosulphuric acid, peroxomonosulphuric acid
and peroxodisulphuric acid are strong oxidizing agents.
REFERENCE:
1. Inorganic chemistry, R.L.Madan
2. Basic inorganic chemistry, Cotton. F.A Willkinson

19. OXYACIDS OF SULPHUR
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LEAD-CHAMBER PROCESS
Pyrite
burner
Dust
catcher’s
Glover
tower
Lead
chamber
Nitre pot
Gay
lussac
tower
Cooler

20. OXYACIDS OF SULPHUR
RABIA AZIZ BS-III CHEMISTRY Page 20
PRODUCTION%
SULPHURIC ACID
SULPHUROUS ACID
PEROXOMONOSULPHURIC ACID
PEROXODISULPHURIC ACID
THIOSULPHURIC ACID
DITHIONOUS ACID

21. OXYACIDS OF SULPHUR
RABIA AZIZ BS-III CHEMISTRY Page 21
peroxomonsulphuric
acid
DITHIONIC ACID
DITHIONOUS ACID
THIOSULPHURIC
ACID
PEROXODISULPHUR
IC ACID
pyrosulphuricacid
sulphuricacid