Important description of HCl acid including properties-preparation-application

Important description of HCl acid in chemistry 


HCl acid is also known as muriatic acid, is a chemical compound of hydrogen and chlorine with molecular formula, HCl. 

It is polar covalent compound. The dipole moment of H–Cl acid is 1.03 Dbye.
The another name of HCl acid are hydrogen chloride, chlorane, spirits of salt, hydronium chloride etc.




HCl acid is a strong mono basic weak acid. The pKa value ofHCl acid is –7. The 100 ml concentrated HCl acid solution contains 39 ml of pure HCl.

The calculated density of concentrated HCl acid is 1.2 g/c.c. Although, HCl acid is a covalent hydride of hydrogen yet it has some ionic character due to high electronegativity of chlorine atom.

Important properties HCl acid in chemistry

Physical state
HCl acid is a gas at room temperature. Because HCl acid can’t form hydrogen bond due to less polarity of  H – Cl bond.

But it is easily compressed to colorless liquid under low temperature and high pressure. The liquid form of HCl gas is known as HCl acid.

Melting and boiling point of HCl acid


The melting and boiling point of HCl acid are, –114áµ’C and –84áµ’C respectively. Due to less polarity of H–Cl bond, HCl acid does not form inter molecular hydrogen bonding. 
That is, HCl molecules remain as an individual molecule. Consequently, the melting point and boiling point of HCl acid is less than HBr and HI 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 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.

Reducing properties of HCl acid


Since the bond dissociation energy of H–Cl bond is higher than H–Br and H–I bond, hence HCl acid is a mild reducing agents.
But some oxidizing agent, such as KMnO4, K2Cr2O7 Pb3O4, PbO2etc, oxidize HCl acid to release chlorine gas.



What is the cause of HCl acid strength ?


It has been experimentally found that HCl acid is a strong acid. The HCl acid solution change the litmus paper color from blue to red.In aqueous solution, HCl acid is dissociated into the following ions, H3O+ and Cl.


Now, HCl acid is reacts with metallic carbonate or bicarbonate and evolved a effervescence of colorless CO2 gas.
Besides, HCl acid reacts with metal oxide and hydroxide to form salt and water.
The above reaction proved that HCl is a strong acid which is also supported by the pKa value of HCl acid [pKa = –7].

HCl acid preparation in laboratory


When a mixture of NaCl and concentrated H2SO4 is heated at different temperature, then hydrogen chloride is obtained.

This preparation method consisting of two step. In the first step, NaCl react with H2SO4 at 150áµ’-200áµ’C temperature, produced NaHSO4 and HCl.

In the second step, the rest of the NaCl reacts with the producing NaHSO4  under  500áµ’-600áµ’C temperature and produce the expected HCl gas.
When HCl gas is dissolved in water, then HCl acid is prepared.



Industrial method for preparation of HCl acid


HCl acid is also prepared industrially by heating a mixture of equimolecular H2 and Cl2 gas.
This is the large scale preparation method of HCl acid in the world.



HCl acid application in chemistry


 HCl acid is an important chemical in chemistry. So, HCl acid has a significant role both in organic and in inorganicchemistry.
HCl acid is very important in industrial production of different goods.  Some important application of HCl acid is discussed below.

Important application as a 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.
For example, anhydrous ZnCl2 and concentrated HCl acid mixture[which is known as Luis reagent],is used for identification of primary, secondary and tertiary aliphatic alcohol.

Important application of HCl acid in industrial purpose


HCl acid is used in industrial production of some important substance, such as, Cl2, NH4Cl, glucose etc.
 Again, in galvanization process, HCl acid 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[ known as aqua regia ], is used as a melting agent of gold, silver etc in industry.

 HCl is used in to prepare of chlorine gas


 HCl acid is used to prepare Cl2 gas, oxidizing it by air oxygen in presence of CuCl2 catalyst in Deacon’s process.
Cl2 gas is also produced on hydrolysis of concentrated HCl acid, in reaction with some  electro-positive metals [ Zn, Mg, Ca etc ].


Others application of HCl acid.


Beside the above uses, HCl acid is used in industry for removal of lubricants from animal bone and also use for its purification.
HCl acid is used to prepare many organic compounds, such as alkyl chloride from alkene and alcohol and glucose, fructose from sugar.





Important description of HCl acid in chemistry
Important properties HCl acid in chemistry
Melting and boiling point of HCl acid
Bond dissociation energy and stability
Reducing properties of HCl acid
What is the cause of HCl acid strength?
HCl acid preparation in laboratory
HCl acid application in chemistry
Important application as a laboratory reagent
Important application of HCl acid in industrial purpose
HCl is used in to prepare of chlorine gas






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