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Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula
NH3.
It is a colourless gas with a characteristic pungent odour.
Ammonia contributes significantly to the nutritional needs of terrestrial
organisms by serving as a precursor to food and fertilizers.
Ammonia, either directly or indirectly, is also a building block for the
synthesis of many pharmaceuticals. Although in wide use, ammonia is both caustic and hazardous. It is
used in commercial cleaning products.
Ammonia is produced industrially by the Haber-Bosch process which
involves the catalytic reduction of nitrogen (obtained by fractional
distillation from liquid air) by hydrogen at temperatures of 450-500 C
and pressures of 35-40 MPa.
Preparatio
Properties Uses
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AMMONIA
Preparation of Ammonia
Ammonia is produced industrially by the Haber-Bosch process which involves the
catalytic reduction of nitrogen (obtained by fractional distillation from liquid air) by
hydrogen at temperatures of 450-500 C and pressures of 35-40 MPa.
This is achieved by increasing the pressure on the reacting system. In practice,
the pressure that is used is around 40 MPa (about 400 times normal atmospheric
pressure).
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Synthesis gas preparation
First, the methane is cleaned, mainly toremove sulfur oxide and hydrogen sulfide impuritiesthat would poison the catalysts.
The clean methane is then reacted with steam overa catalyst of nickel oxide. This is called steamreforming:CH4 + H2O CO + 3 H2
Secondary reforming then takes place with theaddition of air to convert the methane that did notreact during steam reforming.2 CH4 + O2 2 CO + 4 H2CH4 + 2 O2 CO2 + 2H2O
Then the water gas shift reaction yields morehydrogen from CO and steam.CO + H2O CO2 + H2
The gas mixture is now passed into amethanator[8] which converts most of theremaining CO into methane for recycling:CO + 3 H2 CH4 + H2O
This last step is necessary as carbonmonoxide poisons the catalyst. The overallreaction so far turns methane and steaminto carbon dioxide, steam, and hydrogen.
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Ammonia synthesis Haber process
The final stage, which is the actual Haber process, is the synthesis ofammonia using an iron catalyst promoted with K2O, CaO and Al2O3:
N2 (g) + 3 H2 (g) 2 NH3 (g) (H = 92.22 kJmol1)
This is done at 1525 MPa (150250 bar) and between 300 and550 C, passing the gases over four beds of catalyst, with coolingbetween each pass to maintain a reasonable equilibrium constant.
The steam reforming, shift conversion, carbon dioxide removal, andmethanation steps each operate at absolute pressures of about 2.53.5 MPa (2535 bar), and the ammonia synthesis loop operates at
absolute pressures ranging from 618 MPa (60180 bar), dependingupon which proprietary design is used.
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Properties of
Ammonia
soluble in water
combines with water to
form ammonium
hydroxide
Boiling point is
33.35 C (28.03
F), and its freezing
point is 77.7 C
(107.8 F)
colourless gas with a
sharp, penetrating
odour
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Uses ofAmmonia
FertilizerPrecursor tonitrogenouscompounds
Cleaner
Fermentation
Refrigeration R717
As a fuelFor
remediationof gaseous
emissions
Antimicrobialagent for
foodproducts
As astimulant
used fortreatmentof cottonmaterials
used to fillweatherballoons
as a liftinggas
to darkenquartersawnwhite oak inArts & Craftsand Mission
style furniture
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SULPHURIC ACID
Sulphuric
Sulfuric acid is a strong mineral acid with the molecular
formula H2SO4. Its historical name is oil of vitriol.
Pure sulfuric acid is a highly corrosive, colorless, viscous liquid.
The salts of sulfuric acid are called sulfates. Sulfuric acid is soluble
in water at all concentrations.
Sulfuric acid has many applications, and is a central substance in
the chemical industry.
Principal uses include lead-acid batteries for cars and other
vehicles, ore processing, fertilizer manufacturing, oil
refining, wastewater processing, and chemical synthesis.
Sulphuric acid industrially produced by using Contact Process
Preparation Properties Uses
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The contact process is the current method of producingsulfuric acidin the high
concentrations needed for industrial processes. Vanadium(V) oxide is the
catalystemployed.
The process can be divided into three stages:
Preparation and purification ofsulfur dioxide
Catalytic oxidation (usingvanadium oxide catalyst) of
sulphur dioxide to sulfurtrioxide
Conversion of sulphur trioxideto sulphuric acid
Preparation
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Purification of air and SO2 is
necessary to avoid catalyst poisoning(ie. removing catalytic activities).
The gas is then washedwith water and dried by
H2SO4.
To conserve energy, the mixture isheated by exhaust gases from the
catalytic converter by heatexchangers.
Sulphur dioxide and oxygen then react inthe manner as follows:
2SO2(g) + O2(g) 2 SO3(g): H= 197kJ mol1
To increase the reaction rate, hightemperatures (450 C), high pressures (200
kPa or 2 atm), and vanadium(V) oxide(V
2
O5
) are used to ensure a 99.5%conversion. Platinum would be a moresuitable catalyst, but it is very costly and
easily poisoned.
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A flow scheme for this part of the process looks like above.
Making thesulphur dioxide
This can either bemade by burningsulphur in an excess ofair:
. . . or by heatingsulphide ores likepyrite in an excess ofair:
In either case, anexcess of air is used
so that the sulphurdioxide produced isalready mixed withoxygen for the next
stage.
Converting thesulphur dioxide into
sulphur trioxide
This is a reversiblereaction, and theformation of the
sulphur trioxide isexothermic..
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Converting the sulphur
trioxide into sulphuric acid
This can't be done by simply adding waterto the sulphur trioxide - the reaction is souncontrollable that it creates a fog ofsulphuric acid.
Instead, the sulphur trioxide is firstdissolved in concentrated sulphuric acid:
H2SO4 + SO3 H2SO7
The product is known asfumingsulphuric acidor oleum.
H2SO7 + H2O 2H2SO4
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Properties
Propertiesof H2SO4
powerfulprotonating
agent.
moderatelystrong oxidizin
g agent.
powerful
dehydratingagent
strong dibasicacid
powerfuldehydrating
agent
colourless,
hygroscopicliquid
no odour
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Uses ofH2SO4
electrolyte usedin lead-acid
batteries(accumulators)
production offertilizers such asammonium sulfate
(sulfate ofammonia which isformed when rock
phosphate istreated withsulfuric acid.
remove oxidesfrom iron and steelbefore galvanisingor electroplating
Concentratedsulfuric acid (18M)
is used as adehydrating agent,that is, to removewater, since it has
a tendency to formhydrates such as
H2SO4.H2O,H2SO4.2H2O, etc.
used in theproduction of
nitroglycerine, aninorganic ester &
organic nitrate
used as a dryingagent to
chemically removewater from many
substances.
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NITRIC ACID
Nitric Acid, HNO3
Nitric acid (HNO3, also known as aqua fortisand spirit of nitre, is a
highly corrosive and toxic strong acid.
Colorless when pure, older samples tend to acquire a yellow cast due to
the accumulation of oxides of nitrogen.
If the solution contains more than 86% nitric acid, it is referred to
as fuming nitric acid.
Depending on the amount of nitrogen dioxide present, fuming nitric
acid is further characterized as white fuming nitric acid or red fuming
nitric acid, at concentrations above 95%.
Nitric acid is also commonly used as a strong oxidizing agent.
Preparation Properties Uses
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Preparation of Nitric Acid
Nitric acid is made by reaction of nitrogen dioxide (NO2) with water.
3 NO2 + H2O 2 HNO3 + NO
Normally, the nitric oxide produced by the reaction is reoxidized by the oxygen in
air to produce additional nitrogen dioxide
Bubbling nitrogen dioxide through hydrogen peroxide can help to improve acid
yield.
2 NO2 + H2O2 2 HNO3
Almost pure nitric acid can be made by adding sulfuric acid to a nitrate salt, and
heating the mixture with an oil bath. A condenser is used to condense the nitric
acid fumes that bubble out of the solution.
2 NaNo3 + H2SO4 2 HNO3 + Na2SO4
Ostwald Process
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Ostwald Process
Production of nitric acid is via the Ostwald Process, named after German
chemist Wilhem Ostwald.
Further concentration to 98% can be achieved by dehydration with
concentrated H2SO4. By using ammonia derived from the Haber process, the final
product can be produced from nitrogen, hydrogen, and oxygen which are derived
from air and natural gas as the sole feedstocks.
In this process, anhydrous ammonia is oxidized to nitric oxide, in the presenceof platinum or rhodium gauge catalyst at a high temperature of about 500K and apressure of 9 bar.
4 NH3 (g) + 5 O2(g) 4 NO (g) + 6 H2O (g) (H = 905.2 kJ)
Nitric oxide is then reacted with oxygen in air to form nitrogen dioxide.
2 NO (g) + O2(g) 2 NO2(g) (H = 114 kJ/mol)
This is subsequently absorbed in water to form nitric acid and nitric oxide.
3 NO2 (g) + H2O (l) 2 HNO3(aq) + NO (g) (H = 117 kJ/mol)
The nitric oxide is cycled back for reoxidation. Alternatively, if the last step is carriedout in air:
4 NO2 (g) + O2 (g) + 2 H2O (l) 4 HNO3 (aq)
The aqueous HNO3 obtained can be concentrated by distillation up to about 68%by mass.
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Properties ofnitric acid
colorless mobileliquid with a
density of 1.512g/cm3
In liquid state
Transparent to
yellow
As gaseous oxides
Transparent to
yellow or brown
Odour
Sweet to pungent
strong oxidizingagent
both acidic andbasic properties it
can undergo anautoprotolysis
reaction, similar tothe self-ionization
of water
reacts violentlywith many organicmaterials and thereactions may be
explosive.
reacts with mostmetals
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Uses of nitric acid
It is used in the
production ofammonium nitrate for
fertilizers.
It is used for makingplastics
It is used in themanufacture of dyes
used for makingexplosives such as
nitroglycerine
When it is combined
with hydrochloric acid itforms an element called
aqua regia which is areagent that is capableof dissolving gold and
platinum.
used in a colorimetrictest to distinguish heroin
and morphine.
commonly used inscience laboratories at
schools forexperimenting whenspecifically testing for
chloride.
used in the field ofmedicine in its pure stateas a caustic to get rid of
chancres and warts.