Hydrogen chlorideHydrogen chloride is a compound of chlorine and hydrogen and the symbol HCl denotes it. Hydrogen chloride is a gas under normal conditions of air pressure and temperature. When dissolved in water, hydrogen chloride gas is known as hydrochloric acid. Hydrogen chloride is an example of a polar covalent compound.
Hydrogen chloride was prepared for the first time in 1648 by a German-Dutch chemist and alchemist, Glauber. He formed hydrogen chloride by bringing sodium chloride to heat up and concentrated H2SO4. In the year 1840, Davy showed that hydrogen chloride is a compound of hydrogen and chlorine.
How to prepare hydrogen chlorideThere are several uses of hydrogen chloride gas, but it’s important to understand how hydrogen chloride is prepared before we discuss it.
Direct synthesisPure hydrogen chloride can be made by combining hydrogen and chloride. Here is the chemical reaction of combining hydrogen and chlorine :
Cl2 + H2 → 2 HCl
Note that this reaction is exothermic. The hydrogen chloride gas obtained in this process is imbibed in ionised water, making hydrochloric acid. This process gives very pure hydrochloric acid, which is used in many industries like the food industry.
Organic synthesisThe industrial production of hydrogen chloride is a different process. Hydrogen chloride is formed by the integration of chlorinated and fluorinated organic compounds, for instance, PVC, CFCs, Teflon, Freon and chloroacetic acid as well.
In the chemical reaction, the hydrogen atoms in the hydrocarbons are substituted by chlorine atoms, the hydrogen atoms that are released then combine with the idle atoms released from chlorine molecules and hence hydrogen chloride is formed. Here are chemical reactions:
R-H + Cl2 → R-Cl + HCl
R-Cl + HF → R-F +HCl
The hydrogen chloride produced is absorbed in water, which gives hydrochloric acid of the technical or industrial grade.
Use of hydrogen chlorideThere are many uses of hydrogen chloride gas in several industries like the food industry. Here are some of the uses of hydrogen chloride:
- It is used in the production of chlorine and chlorides.
- It is used in tanning industries.
- It is used in dyeing calico printing.
- It is used in several medicines.
- It is an essential reagent in the labs.
- It is used in the production of glucose through the hydrolysis of starch.
- It is used in pickling before galvanising, electroplating and tinning.
- It is used in making aqua regia that is used in dissolving metals such as gold.
Properties of hydrogen chlorideHere are some of the properties of hydrogen chloride:
- Hydrogen chloride is a colourless gas.
- It has a pungent smell
- Hydrogen chloride is soluble in water.
- When hydrogen chloride is liquified at 189 K temperature, a colourless liquid is produced
- Hydrogen chloride can freeze at 159 K temperature. When frozen, hydrogen chloride appears as a white solid substance.
Chemical properties of hydrogen chlorideHere are some chemical properties of hydrogen chloride:
Reaction with litmusDry hydrogen chloride gas has no reaction on litmus. The aqueous solution of hydrogen chloride turns the litmus from blue to red which indicates it is acidic.
OxidationHydrogen chloride is oxidised by atmospheric oxygen in cuprous chloride’s presence to produce chlorine.
4HCl + O2 → 2H2O + 2Cl2
Acidic properties of HClThe aqueous form of hydrogen chloride is acidic and it is almost completely ionised in H2O.
H2O + 4HCl → H3O+ + Cl–
Hydrogen chloride in aqueous form is known as hydrochloric acid. Hydrochloric acid shows all the properties of acid.
As a reducing agentHydrogen chloride acts as a reducing agent as it can be oxidised to chloride with the help of oxidising agents such as potassium permanganate, potassium dichromate and manganese dioxide:
2KMnO4 + 16HCl → 2KCl +
2MnCl2 + 8H2O + 5Cl2
K2Cr2O7 + 14HCl → 2 KCl + 2 CrCl3 + 7 H2O + 3Cl2
MnO2+ 4HCl → MnCl2 + 2H2O + Cl2
Reaction with fluorineWhen reacted with fluorine, it displaces chloride from HCl. Here is a chemical reaction: 2HCl + F2 → 2HF It is important to note here that iodine and bromine don’t react with hydrogen chloride.
Making of aqua regia3 parts of hydrochloric acid in concentrated form is mixed with one part of nitric acid in concentrated form to form what is called aqua regia.
To form nascent chlorine, Hydrochloric acid is oxidised by nitric acid in aqua regia. Here is a chemical reaction:
3HCl + HNO3 →NOCl + 2H2O + 2Cl
Aqua regia is known to dissolve noble metals such as platinum and gold. Here is a chemical reaction:
Au + 3Cl → AuCl3
Au + 4H++ NO3¯ + 4 Cl¯ → AuCl4¯ + NO + 2 H2O
3Pt + 16 H+ + 4NO3‾ + 18 Cl¯ → 3 [PtCl6]2¯ + 4 NO + 8 H2O