Details of hydrochloric acid in chemistry
Hydrochloric
acid is also known as hydrogen chloride, is a chemical compound
of hydrogen and chlorine with molecular formula, HCl.
About 42% of HCl [ in stoichimetric ratio] or concentrated
aqueous solution of hydrogen chloride gas at S.T.P, is known as hydrochloric
acid.
The another name of hydrochloric acid are chlorane, muriaticacid, spirits of salt, chlorhydric acid etc.
Hydrochloric acid formula
Hydrochloric acid is a diatomic molecule with chemical
formula, HCl.
Hydrochloric acid is the salt of hydronium ion( H3O+) and chloride
ion. It is produced when HCl is dissolved in water.
The structure of bulk water
is infamously complex. Infra red spectroscopy, X-ray and neutron diffraction study
of conc.HCl acid solutions revealed that the primary form of H+(aq) in these is
H5O2+.
This form along with chloride anion, is H-bonded to the
neighboring water molecules in several different ways.
In H5O2+, the proton is
sandwiched midway between two water molecules at 180ᵒ. The simple chemical formula and Lewis dot structure of
hydrochloric acid molecule are shown below.
Hydrochloric acid properties
There are two type of properties of hydrochloric acid in
chemistry, namely physical properties and chemical properties.
Most the of the important properties of hydrochloric acid
are discussed below with example.
Hydrochloric acid physical properties
Hydrogen
chloride is an anti-breathing, colorless
gas with pungent smell. It is a polar
covalent compound of hydrogen and chlorine elements. The dipole moment of H–Cl acid is 1.03 D.
In ordinary temperature, HCl is a gas. But it is easily
compressed to colorless liquid and also to white crystalline solid under low temperature and high pressure.
Although, hydrochloric
acid is a covalent hydride of hydrogen yet it has more ionic character due to high electronegativity
of chlorine atom.
Physical
state
Hydrogen chloride is a
gas at room temperature. But it is easily compressed to colorless liquid
and also to white crystalline solid under high temperature and low pressure.
HCl gas is slightly heavier than air. When HCl gas come in
contact with aquatic air it creates white smoke.
Melting and boiling point of hydrochloric acid
The melting point and boiling point of hydrochloric acid are, 159 K and 189 K respectively.
Because, at ordinary temperature, HCl is a gas.
Due
to less polarity of H–Cl bond, hydrogen chloride does not form inter molecular
hydrogen bonding.
That
is, HCl molecules remain as an individual molecule. Hence, HCl is a gas at room
temperature.
Consequently, the melting point and boiling point of hydrochloric acid is less than HBr andHI acids.
Bond dissociation energy and stability
Chlorine
is a strong electronegative element than hydrogen. So, H–Cl bond is more polar
and more strong than H–Br and H–I bond.
Hence,
the bond dissociation energy of H–Cl bond is higher than that of H–Br and H–I
bond. The bond dissociation of H–Cl bond is 432 KJ/mole.
Therefore,
H – Cl is more stable compound than HBr and HI molecules.
Hydrochloric acid density
Hydrogen chloride gas is super soluble in water, when dissolved.
At
273 K temperature and one atmosphere pressure, about 42% of HCl [ in
stoichimetric ratio] or concentrated aqueous solution of hydrogen chloride gas
is known as hydrochloric acid.
The 100 ml concentrated hydrochloric acid solution contains 39 ml of
HCl. The density of hydrochloric acid is1.2 g/ml or 1200 g/litre.
It is a strong mono
basic weak acid. The pKa value of HCl acid is, –7.
Hydrochloric acid laboratory preparation
Hydrogen
chloride is prepared in the laboratory by heating of a mixture of
sodium chloride and concentrated sulfuric acid.
The reactions consist of two step. In the first step, sodium
chloride react with concentrated sulfuric acid at low temperature [ 420K ],
giving NaHSO4 and HCl.
In the second step,
the rest of the NaCl reacts with the producing sodium hydrogen sulfate
at high temperature [ 823K ] and produce the expected hydrogen chloride gas.
The producing hydrogen chloride gas is dried on passing
through the concentrated sulfuric acid.
Industrial method for preparation of hydrogen chloride
When equal volume of hydrogen and chlorine is passed through
a tube into a combustion cell which is made by silica, then HCl gas is
obtained.
The producing hydrogen chloride gas is passing through a
cold cell for cooling.
After cooling, the HCl gas is added to water through
which the expected hydrochloric acid is obtained. This is the large scale preparation method of HCl acid in
the world.
Hydrochloric acid chemical properties
Reducing properties
Since
the bond dissociation energy of H–Cl bond is higher than H–Br and H–I bond,
hence hydrochloric acid is a mild reducing agents.
But
some oxidizing agent, such as, KMnO4, K2Cr2O7,Pb3O4 and PbO2 etc oxidize hydrochloric acid to release chlorine
gas.
Thermal stability of HCl
The
bond dissociation of H – Cl bond is 103 Kcal/mole, which is higher than that of
HBr and HI.
So, the H – Cl bond does not dissociate easily. Hence, HCl is
thermally more stable than HBr and HI.
Hydrochloric acid strength explanation
HCl
gas is highly soluble in water. When HCl gas is dissolved in water, the resulting
aqueous solution is called hydrochloric acid. The aqueous solution produce H3O+
and Cl- ions.
So,
HCl acid is a strong acid The aqueous solution of HCl change the litmus paper
color from blue to red.
Hydrochloric
acid is also reacts with metallic carbonate or bicarbonate, and evolved a
effervescence colorless, odorless CO2 gas.
Besides,
hydrochloric acid reacts with metal oxide and hydroxide to form salt and water.
The above reaction proved that HCl is a strong acid.
Although,
HCl is a stronger acid than HF but it is a weaker acid than HBr or HI.
Hydrochloric acid uses in chemistry
There
are a large number of application of hydrochloric acid as an important chemical
in chemistry. HCl acid play an important role both in
organic and in inorganic chemistry.
HCl
has a great significant in industrial production of different goods. Some important uses of hydrochloric acid is
discussed below.
Hydrochloric
acid use as an important laboratory reagent
Hydrochloric
acid is used as an important laboratory reagent. It is used as a reducing
agent, catalytic reagent, hydrolyzing agent, in the preparation and
identification of many organic compounds.
Anhydrous ZnCl2 and concentrated HCl mixture which is known as Luis reagent, is used for identification of primary, secondary and tertiary aliphatic alcohol.
Hydrochloric acid is also used in industrial production of some important substance, such as metal chloride, chlorine, ammonium chloride and production of glucose from starch.
Again, in galvanization process, HCl is used as a cleaning substance. It is used to clean iron sheet before tin plating or galvanization. That is, for removal of iron oxide layer from the surface of iron sheet.
Most
important use of HCl acid is in the dyeing
industry, in the medicine production industry and in sugar industry.
Hydrochloric acid use as a strong oxidizing agent
Although
HCl acid is a mild reducing agent yet it can use as oxidizing agent with nitric
acid.
The
mixture of concentrated HCl acid and concentrated HNO3 in 3: 1 ratio[ which is
known as aqua regia ] , is used as a melting as well as refining agent.
Actually,
in this case the mixture of concentrated HCl and HNO3 produce
nascent chlorine atom which act as a oxidizing agent and oxidize ‘Au’ to AuCl3.
Hydrochloric acid is used to prepare of chlorine
The
chemical process, in which HCl gas is oxidized by air oxygen in presence of
CuCl2 catalyst to form chlorine, is known as Deacon’s process.
Hydrochloric acid is used to prepare hydrogen
There are some metals, which are electro-positive than hydrogen, react with
dilute HCl and produced hydrogen gas. For
example, zinc, magnesium, iron, calcium etc.
Other
uses of hydrochloric acid.
Beside
the above uses, HCl is used in industry for removal of lubricants from animal
bone and also use for its purification.
HCl
is used to prepare many organic compounds, such as alkyl chloride from alkene
and alcohol and glucose, fructose from sugar.
Details of hydrochloric
acid in chemistry
Hydrochloric
acid formula
Hydrochloric
acid properties
Melting and boiling point of
hydrochloric acid
Hydrochloric
acid density
Hydrochloric
acid preparation
Hydrochloric acid strength
explanation
Hydrochloric acid uses in chemistry
No comments:
Post a Comment