HCl (can be called Student Acid) Uses, Manufacture, Properties and much more of it.

 Hydrochloric acid is the most common acid used in laboratory experiments what make it such like? As we are concerned with chemicals processing technology so are going to discuss how it can be prepared? What are its uses? Which properties make it abundantly useful? Let’s see.

 What is Hydrochloric Acid?

Hydrochloric acid is the water solvent of hydrogen chloride, it is regarded as a strong acid. It has a pungent smell. It is found in the digestive organs of many organisms including Humans.

Industrial Manufacture of HCL:-

HCL is manufactured from the following four different processes. We will go through each one by one.

Ø  From Table Salt (salt method)

Ø  From Chlorine and Hydrogen (Synthetic method)

Ø  Obtained as a by-product

Ø  Bt Hargreaves Operations

 

1. From Table Salt ( Salt Method):-

                     The usual method of preparing Hydrogen Chloride is heating the Table salt (NaCl) with conc.H₂SO₄. This is done in the following steps:-

·    Both reactants are charged to a furnace with an agitator. The reaction starts in cold vigorously but after the sometimes evolution of gas slackens.

·    The reaction mixture is slowly heated to a temperature just below Fusion (863°C) to get the further supply of heat.

·    Then obtained gas undergoes cooling and condensing processes in different chambers.

·    The salt cake (Sodium Sulfate) is continuously discharged.

·    The combustion gases, containing HCl passes through the cooling unit. When they enter, their temperature is 840°C while on leaving it is reduced to 38°C.

·    The cooled gases are then passed through a caked-packed tower where H₂SO₄ mist and other solid impurities are removed.

·    Then it is passed through the silica absorbers where chloride is absorbed in water to produce Hydrochloric Acid.

Exhaust gases from the absorber are scrubbed with water and discharged to the atmosphere.

 

 

 

2. From Chlorine and Hydrogen(Synthetic Process):-

Chemicals required:-

·    Chlorine

·    Hydrogen

Chemical Reaction:-

                     H₂ + Cl₂ → 2HCl

Theory:-

First of all, we must know that this synthetic process produces the purest HCL.

The core concept of this process is that HCL is produced by burning Chlorine and Hydrogen. The purity of acid obtained depends upon the purity of Hydrogen and Chlorine. A slight excess of Hydrogen must be provided for the completion of the reaction. Both the gases are available in a pure state as a by-product of Caustic Soda.

Process:-

The reaction between Hydrogen and Chlorine is highly exothermic and the reaction goes to completion spontaneously. When the gases are cooled in a cooler, the free Chlorine and free Hydrogen combines rapidly when the temperature is 200°C. The gas is almost pure Hydrogen Chloride.

The resulting HCL gas is then absorbed in water in an absorption tank. For the saturation of product HCL, the solution is recycled. The unabsorbed Hydrogen from the top of the absorption tower is returned to the burner.

 

3. As a by-Product:-

By product, HCl is the result of Organic synthesis i.e. Chlorination of Benzene. The exhaust gases are then purified to remove excess Chlorine and volatile Organic constituents are then absorbed to produced HCl.

                     C₆H₆ + Cl₂ → C₆H₅Cl + HCl

                     CH₄ + Cl₂ → CH₃Cl + HCl (Chlorination of Methane)

The reaction does not stop here; the remaining 3 Hydrogen atoms of Methyl Chloride can be successively replaced by Chlorine and more HCl can be produced. The chlorination of aliphatic and aromatic compounds evolve much heat so special equipment is necessary to control the temperature of the reaction.

 

4. By Hargreaves Process:-

The simple chemical reaction of the Hargreaves Process is

                     4NaCl + 2SO₂ + O₂ +2H₂O → 2Na₂SO₄ + 4HCl

A wet SO₂-air mixture is passed through a series of the vertical chamber containing salts lying on the perforated bottom. The process is cyclic. SO₂ enter the chamber containing spent salt which is next to removed. The gas then passes the counter current to the salt and just before leaving the process come across the fresh salt in the chamber most recently added to the line. The operating temperature decreases from 1000°F to 8000°F. The HCl in the gas stream is recovered by conventional methods.

 

Properties of HCl:-

1.       HCl is the solution of Hydrogen Chloride in water.

2.       Pure HCl is a colourless, pungent, poisonous gas at ordinary T and P.

3.       It is a good solvent and easily soluble in polar solvents like alcohol, ether as well as water.

 

Uses:-

·         It is used in pickling (cleaning metal surface) of metals that are to be electroplated.

·         HCl is widely used in the manufacture of Aqua Regia (3:1 a mixture of conc.HCl and conc.HNO₃). it is used for dissolving Gold and Platinum.

·         HCl is a Strong Acid but it is much easier to control than other acids so it is widely used in Labs for experimentation.

·         Its familiar use in Industry is pH control and neutralization.

·         It is used in the regeneration of ion exchangers.

·         HCl is also used in the production of Organic Compounds, Metal Oxides, Metal and Metal Carbonates.