Hydrogen chloride preparation and properties, Group 17 P Block Elements
Hydrogen Chloride (HCl) :
→ Hydrogen chloride is a major industrial chemical. It is widely used as laboratory regent. First time in 1648 Glauber prepared it by heating the common salt (NaCl) with concentrated sulphuric acid (H2SO4).
→ In 1810, Davy proved that it is a compound of hydrogen and chlorine. When hydrogen combines with chlorine then a covalent compound HCl is formed. In anhydrous state it is not acidic in nature but in aqueous state it release H+ lona thus, it is also called hydrogen acids or hydra acid. Priestely called it ‘marine acid’ and Lavoisier called it ‘Quriotic acid’.
It can be prepared by the following methods:
→ Laboratory Method : In laboratory, it can be prepared by heating sodium chloride (rock salt) with concentrated sulphuric acid.
It can be dried by passing it through concentrated sulphuric acid
→ Above process can also be used for commercial preparation Commercially it can be manufactured by heating NaCl and conc. H2SO4 in Muffle furnace.
→ By ammonium chloride : When ammonium chloride is heated with consulphuric acid then HCl is formed
2NH4 + Cl + H2SO4 → (NH4)2 SO4 + 2HCl
→ Industrial preparation in large scale HCI can be prepared as a byproduct from the heavy organic industry. It can be prepared during the conversion of 1.2.dichloroethane into vinyl chloride
Physical properties of Hydrogen chloride
Some important physical properties of hydrogen chloride are as follows:
- It is colourlons, pungent Amelling gas
- It can easily be liquified into colorless liguid
- It is highly soluble in water and its aqueous solution is known as hydrochloric acid
- It fumes in moist air.
- Its boiling point is 189K
- It freezes into white crystalline solid. Its freezing points in 169 K
- It is heavier than air. Itu vapour density is 18.25.
Chemical properties of Hydrogen chloride
→ Action on Htmus : Dry HCL cannot chnage the colour of litmus but its aqueous solution can tum blue litmus red which indicates that it is acidic in nature.
→ Acidic behaviour. In aqueous solution it ionises and produce hydronium ion (H3O+) and chloride ion (Cl–)
HCl(g) + H2O(l) → H3O+(aq) + Cl–(aq), Ka = 107
→ Its dissociation constant (Ka) is very high which indicates that it is a very strong acid in water. Some acidic properties of hydrochloric acid are as follows:
→ Reaction with metals: It reacts with active metals like sodium, potassium, magnesium, iron zinc etc. and liberate hydrogen gas :
→ Reaction with ammonia: It reacts with ammonia and give white fumes of NH4Cl.
→ Reaction with bases : It reacts with bases like hydroxides, carbonates, bicarbonate of metals to form chlorides
→ Reaction with salts : HCl can decomposes the salts like Na2S, NaNO2, Ca3P2, Na2SO3 etc.
→ Precipitation Reactions : HCl can form the precipitate of chlorides when it reacts with salts of Ag. Pb and Hg.
→ Reaction with fluorine : Fluorine can displace chlorines from HCl
2HCl + F2 → 2HF + Cl2
→ Oxidation : HCl can be oxidised by atmospherie oxygen in the presence of Cu2Cl2 catalyst at 723K temperature to produce chlorine PR This reaction is used in Deacon’s process.
→ As a reducing agent : It behaves as a reducing agent because it can be oxidised into chlorine by strong oxiding agents such as K2Cr2O7, KMnO4, MnO2 etc.
→ Formation of Aqua regia: A mixture of three parts of concentrated hydrochloric acid and one part of concentrated nitric acid is known as aqua regia. In aqua regia HCl acts as reducing Agent while HNO acts us oxidising agent. Aqua regin is used to dissolve noble metals Nike Au, Ptete.
Uses of Hydrogen chloride
- In manufacturing of dyestuffs and in sugar industry.
- In preparation of chlorine, ammonium chloride, metal chlorides etc.
- In preparation of aqua regia.
- In medicine and used as laboratory reagent.
- For extracting glue from animal tissues and bones.
- In pickling or cleaning metallic surfaces ie surface of oxide layer over metal before subjecting it for tin plating, galvanising and electroplating.