Hydrogen Chloride: Properties, Preparation, Uses

Hydrogen Chloride: The compound hydrogen chloride \(\left( {{\rm{HCl}}} \right)\) is a hydrogen halide with the chemical formula \({\rm{HCl}}\). It is a colourless gas at room temperature that produces white hydrochloric acid fumes when it comes into contact with atmospheric water vapour. In technology and industry, hydrogen chloride gas and hydrochloric acid are important. To learn more about hydrogen chloride, read the below article.

Hydrogen Chloride (HCl): Formula

As early as \(800{\rm{ A}}.{\rm{D}}.\), Glauber \(\left( {{\rm{1648}}} \right)\) prepared hydrochloric acid by heating a mixture of rock salt and conc. sulphuric acid. Joseph Priestley \(\left( {{\rm{1772}}} \right)\) obtained it from sea salts and named it as marine acid. Later, in \(1810\), Lavoisier named it muriatic acid, and Sir Humphry Davy demonstrated that it was a compound of hydrogen and chlorine, naming it hydrochloric acid.

Hydrogen chloride gas occurs in the state of volcanic gases. It is also present in the gastric juice of mammals: including human beings. Hydrogen chloride does not produce hydrogen ions in a gaseous state, but it produces hydrochloric acid when dissolved in water. So, in an aqueous solution, hydrogen chloride gas gives a \({\rm{pH}}\) value of about \(3.01.\) The chemical formula of hydrogen chloride is \({\rm{HCl}}\).

Lewis Structure of Hydrogen chloride

Hydrogen chloride is a gas, as we have seen. A Lewis dot structure of \({\rm{HCl}}\left( {\rm{g}} \right)\) can be shown to demonstrate the electron configuration in the hydrogen-chlorine bond. The Lewis dot structure of hydrogen chloride gas is depicted in the diagram. The dots in the diagram represent electrons in the outer shell. The hydrogen and chlorine atoms share two electrons, making this a covalent molecule.

Preparation of Hydrogen Chloride Gas

The preparation methods of hydrogen chloride are explained below:

I. General Methods

i. Hydrogen chloride can be prepared by a direct combination of elements: Hydrogen chloride gas can be produced by combining moist hydrogen and chlorine in the presence of diffused sunlight. This reaction is catalyzed by moisture. The reaction is carried out in diffused sunlight because it is explosive in direct sunlight and is very slow in the dark.

ii. Hydrogen chloride can be prepared by reacting a metallic chloride with concentrated \({{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\): When metallic chlorides react with concentrated sulphuric acid, hydrogen chloride gas is evolved.

II. Laboratory Method

In the laboratory, hydrogen chloride gas can be easily produced by the action of concentrated sulfuric acid on sodium chloride. The apparatus consists of a round bottom flask fitted with a thistle funnel and a delivery tube, the other end dips in cone \({{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\) taken in a Woulfe’s bottle.

A delivery tube connected to the other mouth of the Woulfe’s bottle is taken to a gas jar. Sodium sulfate hardens and sticks to the bottom of the flask, making it difficult to remove. As a result, it is preferable to keep the reaction temperature around \(200\,^\circ {\rm{C}}.\)

The apparatus used is:

The reaction takes place in this process as follows:

Above \({200^{\rm{o}}}{\rm{C}}\), sodium sulphate is formed:

Drying of the Gas (Purification of Gas)

The resulting hydrogen chloride gas contains moisture, i.e., water vapours. It can be dried using conc. \({{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\) (taken in a Woulfe’s bottle). Because it does not react chemically with the \({\rm{HCl}}\) gas, conc. \({{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4}\) is an appropriate drying agent for this purpose. It simply absorbs water. Other drying agents, such as quick lime \({\rm{(CaO)}}\) and phosphorus pentoxide \(\left( {{{\rm{P}}_2}{{\rm{O}}_5}} \right)\), cannot be used for drying \({\rm{HCl}}\) gas because they chemically react with it.

Collection

i. The hydrogen chloride gas is collected by upward displacement of air. This is because it is \(1.27\) heavier than air.
ii. It is not collected over water since it is highly soluble in water.

Physical Properties of Hydrogen Chloride Gas

1. Colour and odour: Hydrogen chloride is a colourless gas with a pungent odour.
2. Physiological nature: It has a corrosive nature. It produces mild corrosion or burning sensation in the nose, throat, and lungs when inhaled.
3. Density: It is about \(1.27\) times heavier than air.
4. Boiling point and Melting point: Hydrogen chloride gas has a boiling point of \(- 85.05\,^\circ {\rm{C}}\) and a melting point of \( – 114.2\,^\circ {\rm{C}}\).
5. Liquefaction and solidification: It liquefies to a colourless liquid when subjected to high pressure (40 atm.) at low temperature \(\left( {10\,^\circ {\rm{C}}} \right)\).
6. Solubility: Hydrogen chloride gas is highly soluble in water (\(1\) volume of water dissolves \(452\) volumes of the gas at room temperature). Because \({\rm{HCI}}\) is a polar covalent compound, it is also soluble in organic polar aprotic solvents such as acetone and toluene.

Experiment To Demonstrate Solubility of Hydrogen Chloride Gas

The great solubility of hydrogen chloride gas can be demonstrated by means of the Fountain Experiment.

Fountain Experiment

1. Take a dry round-bottomed flask filled with dry \({\rm{HCI}}\) gas.
2. Arrange the apparatus as shown below.
3. On the mouth of the flask, fix a rubber stopper with two holes.
4. Through one hole pass a long jet tube, and through another hole pass a dropper with few drops of water.
5. Put the jet tube in the beaker containing blue litmus solution.
6. Press the dropper. It is seen that the blue litmus solution enters the jet tube with a great force, forming a red fountain.

Reason: As water flows into the flask from the dropper, the \({\rm{HCI}}\) gas present dissolves due to its high solubility, lowering the pressure inside. The outside pressure being higher forces the blue litmus solution inside through the jet tube. Because hydrogen chloride gas (in an aqueous solution) is acidic, the blue litmus solution turns red.

Chemical Properties of Hydrogen Chloride Gas

1. Combustibility: Hydrogen chloride gas is neither combustible nor a supporter of combustion. It extinguishes a burning splint.
2. Thermal dissociation: When hydrogen chloride is heated above \(500\,^\circ {\rm{C}}\), it dissociates to produce hydrogen gas and chlorine gas.

3. Reaction with ammonia: Hydrogen chloride reacts with ammonia to form dense white fumes of ammonium chloride.

\({\rm{HCl}}\left( {\rm{g}} \right) + {\rm{N}}{{\rm{H}}_3}\left( {\rm{g}} \right) \to {\rm{N}}{{\rm{H}}_4}{\rm{Cl}}\left( {\rm{s}} \right)\)

4. Reaction with metals: When hydrogen chloride gas is heated with several metals such as \({\rm{Zn}},\,{\rm{Mg}},\,{\rm{Fe}}\), etc., then respective metal chlorides are formed with the evolution of hydrogen gas.
For example:

\({\rm{Zn}} + 2{\rm{HCl}}\left( {\rm{g}} \right) \to {\rm{ZnC}}{{\rm{l}}_2} + {{\rm{H}}_2}\left( {\rm{g}} \right)\)

\({\rm{Mg}} + 2{\rm{HCl}}\left( {\rm{g}} \right) \to {\rm{MgC}}{{\rm{l}}_2} + {{\rm{H}}_2}\left( {\rm{g}} \right)\)

\({\rm{Fe}} + 2{\rm{HCl}}\left( {\rm{g}} \right) \to {\rm{FeC}}{{\rm{l}}_2} + {{\rm{H}}_2}\left( {\rm{g}} \right)\)

5. Non-acidic nature: Dry hydrogen chloride gas is non-acidic in nature due to the absence of \({{\rm{H}}^ + }\) ions. It does not cause dry blue litmus paper to turn red. It only exhibits acidic properties when wetted with water, i.e. when dissolved in water.

Uses of Hydrogen chloride

1. HCI is used to make chlorine, aqua regia, and other chlorides.
2. It is used in laboratories as a reagent.
3. Hydrogen chloride is used as a solvent to dissolve noble gases.
4. Hydrogen chloride has a wide range of applications, including cleaning, pickling, electroplating metals, tanning leather, and refining and manufacturing a wide range of products.

Hydrogen Chloride vs Hydrochloric Acid

Both hydrogen chloride and hydrochloric acid have the chemical formula \({\rm{HCI}}\). The main distinction is their current status. Hydrochloric acid is an aqueous solution of hydrogen chloride, which is a gas. Aqueous simply means it’s dissolved in water. This is why it is important to include the current state of affairs in parentheses. We write \({\rm{HCl}}({\rm{g}})\) for the gaseous version and \({\rm{HCl}}({\rm{aq}})\) for the aqueous version.

Summary

The compound hydrogen chloride is a hydrogen halide with the chemical formula \({\rm{HCl}}\). Hydrogen chloride does not produce hydrogen ions in a gaseous state, but it produces hydrochloric acid when dissolved in water. Hydrogen chloride is a covalent molecule. It is a colourless gas with a pungent odour. Hydrogen chloride has a wide range of applications, including cleaning, pickling, electroplating metals, and manufacturing various products.

FAQs on Hydrogen Chloride

Let’s look at some of the commonly asked questions about Hydrogen Chloride:

Q.1. Why is hydrogen chloride a gas at room temperature?
Ans: Hydrogen chloride is a gas at room temperature. This is because, at room temperature, the motion of the molecules easily overcomes the weak intermolecular forces of hydrogen chloride molecules.

Q.2. What is the correct Lewis structure for hydrogen chloride HCl?
Ans: The Lewis structure of hydrogen chloride is

Q.3. Is hydrogen chloride a solid, liquid or a gas?
Ans: Hydrogen chloride is a gas.

Q.4. What is the difference between hydrogen chloride and hydrochloric acid?
Ans: Both hydrogen chloride and hydrochloric acid have the chemical formula \({\rm{HCl}}\). The main distinction is their physical states. Hydrochloric acid is an aqueous solution of hydrogen chloride, which is a gas.

Q.5. What is the use of hydrogen chloride?
Ans: Following are the uses of hydrogen chloride
1. \({\rm{HCl}}\) is used to make chlorine, aqua regia, and other chlorides.
2. It is used in laboratories as a reagent.
3. Hydrogen chloride is used as a solvent to dissolve noble gases.

Q.6. What does hydrogen chloride smell like?
Ans: Hydrogen chloride has a pungent odor.

Study Everything About Hydrogen Here

We hope this article on ‘Hydrogen chloride’ has helped you. If you have any queries, drop a comment below and we will get back to you.