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•Sulphuric acid is a highly corrosive strong mineral acid with the molecular
•It is a pungent, colorless slightly yellow viscous liquid which is soluble in
water at all concentrations.
•Sometimes, it is dyed dark brown during production to alert people to its
•It is an oxidising agent and a dehydrating agent.
• It freezes at 283k and boils at 611k .
•ST. LOUIS, MO (February 1999) -- Monsanto Enviro-Chem Systems, Inc. has
has completed the construction and startup of the largest single train
sulphuric acid plant in the world.
It is the method used to manufacture sulphuric
acid needed for industrial processes
• Combining of sulphur and oxygen
• Purifying sulphur dioxide in the purification unit;
• Adding excess of oxygen to sulphur dioxide in
presence of catalyst vanadium oxide, (temp - 450
degrees Celsius and pressure of 1-2 atm) to form
• The sulphur trioxide formed is added to sulphuric
acid which gives rise to oleum (disulphuric acid);
• The oleum then is added to water to form
sulphuric acid which is very concentrated.
SO3 is not directly passed in water, because a dense fog of minute
particles of H2SO4 is produced(which is highly corrosive). It
is therefore, dissolved in conc.H2SO4 to form pyrosulphuric acid
Platinum was formerly employed as a catalyst for the reaction, but
as it is susceptible to poisoning by arsenic impurities in the sulphur
feedstock, vanadium(V) oxide (V2O5) is now preferred.
The process can be summarized by the following equations-
S + O2 →SO2
4FeS2 +11O2 →2Fe2O3 +8SO2
2SO2 +O2 →2SO3 +45 Kcal
SO3 + H2SO4 → H2S2O7 (OLEUM)
H2S2O7 + H2O → 2H2SO4
Why is H2SO4 called the ‘king of acids’?
• Sulphuric acid is involved, in some way or the other, in the
manufacture of practically everything.
• Certain chemicals, explosives, acids, dyes, glue, wood
preservatives, automobile batteries, fertilizers, and soaps are some
of the things manufactured with the help of this acid.
• It is used in the purification of petroleum, the pickling of metal,
copper smelting, electroplating, metal work, and the production of
rayon and film.
• 60% of all sulphuric acid produced is mixed with crushed phosphate
rock to make phosphoric acid which primarily has two uses - to
make phosphate fertilizers, and to make sodium triphosphate (a
• Indeed, the production of sulphuric acid is sometimes used as a
measure of how industrially advanced a country is. India produces
about 48 lakh tonnes of this acid a year.
New and improved uses for
One of the most promising uses for sulphur comes from a Shell-patented
technology that adds a mix of elemental sulphur and sulphate to fertilisers.
Shell Thiogro technology makes sulphur — a vital nutrient for many crops —
more readily available to plants throughout the growing season.
The benefits of more effective sulphur use in fertiliser could be significant:
tests on crops by Shell and the Sulphur Institute in the USA showed it
can increase yields by 14% on average in sulphur deficient soils.
Sulphur is also widely used in the construction industry. For example,
adding sulphur pellets to asphalt helps make road surfaces more durable
and resistant to extreme high and low temperatures.
Reaction with water
•Because the hydration energy of sulphuric acid is highly exothermic , dilution should always be performed by
adding the acid to the water rather than the water to the acid. Because the reaction is in an equilibrium that
favors the rapid protonation of water, addition of acid to the water ensures that the acid is the limiting reagent.
This reaction is best thought of as the formation of hydronium ions:
H2SO4 + H2O → H3O+ + HSO4
•Because the hydration of sulphuric acid is thermodynamically favorable and the affinity of it for water is
sufficiently strong, sulphuric acid is an excellent dehydrating agent. Concentrated sulphuric acid has a very
powerful dehydrating property, removing water (H2O)from other compounds including sugar and other
carbohydrates and producing carbon , heat, steam, and a more dilute acid containing increased amounts of
hydronium and bisulfate ions.
C12H22O11 + H2SO4 → 12 C + 11 H2O + H2SO4
As an acid, sulphuric acid reacts with most bases to give the corresponding sulphate.
CuO(s) +H2SO4(aq) → CuSO4(aq) +H2O(l)
Sulphuric acid can also be used to displace weaker acids from their salts.
H2SO4 + CH3COONa →NaHSO4 +CH3COOH
H2SO4 + KNO3 →HNO3 + K2SO4
Reactions with metals and strong oxidising property
Dilute sulphuric acid reacts with metals via a single displacement reaction as with other typical
acids , producing hydrogen gas and salts (the metal sulphate).
3Fe(s)+ H2SO4(aq) → H2(g)+FeSO4(aq)
Concentrated sulphuric acid is a strong oxidizing agent and does not react with metals
in the same way as other typical acids . Sulfur dioxide , water and SO4
2− ions are
evolved instead of the hydrogen and salts.
2H2SO4 + 2e- → SO2 + 2H2O + SO4
It can oxidize non-active metals such as tin and copper , depending upon the
temperature of it like the nitric acid.
Cu + 2H2SO4 → SO2 + 2H2O + SO4
2− + Cu2+
Reactions with non-metals
Hot concentrated sulphuric acid oxidizes non-metals such as carbon and sulphur .
C + 2H2SO4 → CO2 + 2SO2 + 2H2O
S + 2H2SO4 → 3SO2 + 2H2O
•Reactions with sodium chloride
It reacts with sodium chloride , and gives hydrogen chloride gas and sodium bisulphate.
NaCl + H2SO4 → NaHSO4 + HCl
•Electrophilic aromatic substitution
Benzene undergoes electrophilic aromatic substitution with sulphuric acid to give the
corresponding sulphonic acids.
• Hazard Risks - The common ways a worker can be exposed to sulphuric acid include
contact with the skin or eyes ; inhalation of the acid is also a potential risk, and
swallowing sulphuric acid can cause internal damage. Safety procedures should be put
into place for any worker who handles sulphuric acid and any group of workers for
whom inhalation exposure can occur.
• Always wear protective goggles, gloves and a lab coat, as concentrated H2SO4 causes
serious damage to skin and clothing, charring it .
• When diluting H2SO4, add small volumes of the acid to large volumes of water to
disperse heat whilst mixing thoroughly. During pouring of the liquid, pouring down the
sides prevents splashing.
• Work near a running supply of water. If the acid contacts the skin, it must be washed off
rapidly with copious amounts of tap water (however with large spills onto the skin, wipe
off excess first).
• Have a supply of neutralizer (sodium carbonate or bicarbonate) in case it is split. It
should be first isolated to prevent it spreading and the area evacuated in case of fumes.
Sand and a bucket can be used to clear acid for neutralization.
• Store the acid in smaller, easier to handle bottles (<1L). Avoid dribbling acid down the
sides of containers, and wipe off any as soon as possible if present. Always place the
bottle in a drip tray to ensure that do not contact the bench or shelf.
• Treating Exposures
– Any area in which sulphuric acid is used should contain a safety shower, an eyewash
station and clean chemical suits and gloves as well as emergency respirators.
– If a worker gets the acid on her skin, flush the skin immediately with water and
remove any clothing that the acid has eaten through to cause the exposure.
– If acid gets into a worker's eyes, flush her eyes with water.
– Swallowing sulphuric acid will cause immediate burns to the mouth, esophagus and
stomach; if this happens, drink large amounts of water to neutralize the acid; however,
don't encourage vomiting, which will expose the damaged areas a second time as the
acid comes back up.
– For exposure to fumes, get the worker to fresh air. Get medical help as soon as
possible after any type of exposure to sulphuric acid.
• Surface Exposures
– In the case of small or large spills of sulphuric acid, two methods can be used for
– Either dilute the acid with water as quickly as possible, or
– use an absorbent material to soak up and neutralize it.
– Dry sand, soil or vermiculite are common materials used to absorb sulphuric acid.