Short description of HCl chemistry for class 12
HCl chemistry is an important part of chemistry, especially in inorganic chemistry, which is related to the HCl acid.
HCl chemistry gives us a lot of information about HCl
acid. From HCl chemistry, we know about the discover history of HCl acid.
This part of
chemistry is also inform us about the laboratory as well as industrial
preparation of HCl acid, physical and chemical properties of HCl acid,
identification and important application of HCl acid.
A short description of HCl chemistry is discussed
below.
HCl acid discover back ground in chemistry
Scientist Priestley was the first discover of HCl acid.
He discovered the HCl acid in 1772 from sea salt and named muriatic acid, whose
means sea water.
A small amount of HCl acid remain in human stomach.
Sometimes, HCl acid in the gaseous form evolved from volcano.
Industrial method for preparation of HCl acid
When equi-molecular of hydrogen and chlorine is passed through a tube into a combustion silica cell, then HCl gas is obtained.
The producing HCl gas is passing through a cold cell for cooling. After cooling, the HCl gas is dissolved in water to produce HCl acid. This is the large scale preparation method for HCl acid.
Laboratory method for preparation of HCl acid
HCl gas is prepared in the laboratory by heating of a mixture of sodium chloride and concentrated sulfuric acid.
The reactions take place in two step. In the first step, NaCl react with concentrated sulfuric acid at 420K temperature, giving NaHSO4 and HCl.
In the second step, the rest of the NaCl reacts with the producing NaHSO4 at 823K temperature and produce the expected HCl gas. When dissolve in water, it gives HCl acid.
Important properties of HCl acid
HCl acid in gaseous form is an anti-breathing, colorless with pungent smelling gas. It is slightly heavier than air and creates a white smoke with wet air.
HCl gas is easily soluble in water. When it dissolved
in water, it forms a constant boiling mixture with 42% HCl.
At S.T.P, the concentrated aqueous solution of hydrogenchloride is known as hydrochloric acid. The other name of HCl acid is muriatic acid, chloro
hydride, chlorane etc.
The density of hydrochloric acid is 1.2 g/c.c. It is a strong
mono basic acid. The pKa value of
HCl acid is –7.
Physical state
HCl is a gas at room temperature. Because, it can’t form inter-molecular hydrogen bond. But it is easily compressed to colorless liquid under low temperature and high pressure.
Melting and boiling point of HCl acid
Due to less polarity of H–Cl bond, hydrogen chloride can’t form inter- molecular hydrogen bond. 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 HCl acid is less than that of HBr and HI acids. The melting point and boiling point of hydrochloric acid are, 159 K and 189 K respectively.
Bond dissociation energy and stability
Chlorine
is a strong electronegative element than hydrogen. So, H–Cl bond is more polar
and more strong. Hence the bond dissociation of H–Cl bond is 432 KJ/mole.
Reducing properties of HCl acid
Hydrogen chloride is a mild reducing agents. Some
oxidizing agent, such as KMnO4, K2Cr2O7 Pb3O4, PbO2 etc, oxidize HCl acid to
release chlorine gas.
Thermal stability of HCl acid
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.
HCl acid strength
HCl
gas forms hydrochloric acid, when dissolve in water. The concentrated aqueous
solution of hydrogen chloride is known as hydrochloric acid. The aqueous solution of HCl
acid produce H3O+ and Cl- ions.
So, HCl acid is a strong acid. It changes the litmus paper color from blue to red.
Hydrochloric
acid is also reacts with metallic carbonate or bicarbonate, and evolved effervescence
of CO2 gas.
Besides,
hydrochloric acid reacts with metal oxide and hydroxide to form salt and water.
The above experiment proved that HCl is a strong acid.
Important application of HCl acid in chemistry
HCl acid plays an important role, both in organic and in inorganic chemistry. Some important application of HCl acid is discussed below.
HCl acid is used as an important laboratory reagent
HCl
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.
HCl
acid is used in industrial production of some important substance, such as
metal chloride, ammonium chloride and production of glucose.
Again,
in galvanization process, HCl is used as a cleaning substance. It is used to
clean iron sheet before tin plating or galvanization.
Most
important use of HCl acid is in the dyeing industry, in the medicine production
industry and in sugar industry.
The
mixture of concentrated HCl acid and concentrated HNO3 in 3: 1 ratio
is used as an oxidizing solution.
HCl acid is used in to prepare of chlorine
When
HCl is oxidized by air oxygen in presence of CuCl2 catalyst,
chlorine gas is obtained. Chlorine
gas is also produced on hydrolysis of concentrated HCl acid.
HCl
acid is used in to prepare of hydrogen
There
are some metals which are electro-positive than hydrogen, are react with dilute
HCl and produced hydrogen gas.For
example, zinc, magnesium, iron, calcium etc.
HCl
acid is used in the preparation of pure NaCl.
The
concentrated solution of NaCl is known as brine solution. If a specific amount
of HCl is added to this concentrated solution of HCl, then the pure NaCl is
precipitated due to common ion effect.
Due
to common Cl– ion, the solubility product of NaCl increases and hence it is
easily precipitated.
Other uses of HCl 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.
Identification of HCl acid
When
a mixture of concentrated HCl acid and a little amount of MnO2 dust is heated
in a test tube, a greenish yellow color of gas with pungent smell is evolved.
This
emitted gas change the color of KI in starch solution, from greenish yellow to
blue. The above experiment identify the HCl acid solution.
Why is aqueous solution of HCl conduct electricity in spite of covalent substance?
Chlorine is a strong electronegative element than hydrogen atom. Hence, in case of H – Cl bond, chlorine atom pull the covalently bonded electrons towards itself.
As a result, chlorine atom gets partial positive charge and hence hydrogen atom gets partial negative charge. That is, the HCl molecule becomes polar.
Therefore, if the HCl gas is added to water, it ionized into H+ and Cl–ions. This H+ ion is then attached with water molecule by gain lone pair of electrons of oxygen atom and form H3O+ ion.
In this way, HCl produce H3O+ and Cl–ion when dissolved in water. Since the ions of a substance conduct electricity, hence aqueous solution of HCl conduct electricity.
But anhydrous HCl does not conduct electricity. Because, pure liquid or gaseous HCl can’t form any ions, hence hydrogen chloride gas can’t conduct electricity.
Short description of HCl chemistry for
class 12
HCl acid discover back ground in chemistry
Important properties of HCl acid
Properties
of HCl acid in chemistry
Important
application of HCl acid in chemistry
Identification
of HCl acid
Why is aqueous solution of HCl acid conduct electricity
in spite of being covalent ?
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