How Hydrogen Chloride Is Made and Used in Everyday Life
In Chemistry, even though Chlorine and Hydrogen Chloride is given as different elements, we always tend to study them together. They both share a closer relationship. For example, most of the HCl is produced as a co-product of the reactions by involving chlorine. Therefore, basically, this makes it desirable to consider both the chemical substances together. As being said, let us look at the methods for the preparation of Chlorine and Hydrogen Chloride.
Hydrogen Chloride
Firstly, Hydrogen Chloride was prepared in 1648 by Glauber by the process of heating sodium chloride with the concentrated H2SO4. Whereas, in 1840, Davy explained that HCl is a compound mixed with hydrogen and chlorine. The hydrochloric acid common name is given as muriatic acid.
Production of Hydrogen Chloride
Most of the hydrogen chloride produced on an industrial scale can be used for hydrochloric acid production.
Direct Synthesis
Very pure hydrogen chloride can be produced by combining the chlorine and hydrogen. The chemical reaction for the same is given as follows:
Cl2 + H2 → 2 HCl
Since the reaction is exothermic, we can refer to the installation as either an HCl burner or an HCl oven. The resultant hydrogen chloride gas can be absorbed in deionized water by resulting in the chemically pure hydrochloric acid. Also, this reaction gives a very pure product, for example, for the food industry usage.
Organic Synthesis
Hydrogen chloride’s industrial production is often integrated by forming fluorinated and chlorinated organic compounds, For example, Freon, Teflon, and other CFCs and chloroacetic acid, PVC well, etc. The production of hydrochloric acid is often integrated with its captive on-site use. In the case of chemical reactions, hydrogen atoms present on the hydrocarbon can be replaced by the chlorine atoms, whereupon the hydrogen atom which is released recombines with the spare atom from the chlorine molecule by forming the hydrogen chloride. Fluorination is given as a subsequent reaction of chlorine-replacement by producing again hydrogen chloride, where the chemical reaction can be given as follows:
R−H + Cl2 → R−Cl + HCl
R−Cl + HF → R−F + HCl
The resultant hydrogen chloride can be either absorbed in water or reused directly, resulting in hydrochloric acid of industrial or technical grade.
Properties of Hydrogen Chloride
HCl has a pungent aroma, and it is an uncoloured gas.
Hydrochloric acid is given as the aqueous solution of the hydrogen chloride.
HCl is soluble in water.
It liquefies at a temperature of 189K to produce a colourless liquid and freezes at a temperature of 159k to produce a white solid.
Uses of Hydrogen Chloride Gas
HCl can be used in the preparation of aqua regia, chlorine, including other chlorides.
It can also act as a reagent in laboratories.
It can be used as a solvent to dissolve noble gases.
Chlorine
Chlorine holds an atomic number 35, and in the periodic table, this compound occupies group 17 and period 3. The chemistry behind chlorine plays a key role in meeting the everyday requirements. Scientists around the world are working on the advancements in modern medicines and renewable energies. In 1774, Scheele discovered the presence of this greenish-yellow gas by noticing the HCl action on MnO2. This particular gas was not given a name until Davy had rooted its elementary description and recommended the name according to the colour of the gas.
Preparation of Cl2
The chlorine gas can be prepared using any of the following processes:
When the Manganese dioxide is heated with concentrated HCl. The reaction is given as follows:
MnO2 + 4HCl → MnCl2 + Cl2+ 2H2O
Concentrated HCl acid is replaced by a combination of common salt and concentrated H2SO4. The reaction is given as follows:
4NaCl + MnO2 + H2SO4 → MnCl2 + 4NaHSO4 + 2H2O + Cl2
HCl in action with pottasium permanganate results in the following reaction:
2KMnO4 + 16HCl → 2KCl + 2MnCl2 + 8H2O + 5Cl2
Other Processes to Prepare Chlorine
Deacon’s Method: In this specific method, Cl2 is obtained by oxidizing the HCl gases with oxygen in the catalyst presence. CuCl2 also acts as a catalyst at 723k in this process.
Electrolytic Process: In this particular process, brine undergoes electrolysis. Brine is defined as a concentrated solution of sodium chloride. After the process of electrolysis, Cl2 is discharged at the anode.
Properties of Cl2
Cl2 is given as a gas having a pungent odour and greenish-yellow colouration.
The gas nature is poisonous.
This gas boils at a temperature of 239.11K and melts at a temperature of 171.6K.
Chlorine water can be produced when Cl2 is dissolved in water. The yellow colour of the water becomes dissipated when exposed to the sunlight because of HCl and hypochlorous acid formation. This particular hypochlorous acid, which is formed, is unstable, and hence it decomposes to form nascent oxygen, which is responsible for oxidizing and bleaching action of Cl2.
Cl2 + → H2O (sunlight) HCl + HOCl
2HOCl + 2HCl → 2[O]
Cl2 is also highly electronegative in nature
Cl2 gas contains a great affinity towards hydrogen, and it reacts with hydrogen to produce HCl.
FAQs on Hydrogen Chloride: Properties, Preparation, and Applications
1. What is Hydrogen Chloride (HCl)?
Hydrogen Chloride, with the chemical formula HCl, is a diatomic molecule consisting of a hydrogen atom and a chlorine atom. At room temperature, it is a colourless gas with a sharp, pungent odour. When it dissolves in water, it forms hydrochloric acid, which is a strong acid commonly used in laboratories and industries.
2. What are the key physical and chemical properties of Hydrogen Chloride?
Hydrogen Chloride exhibits several distinct properties:
- Physical Properties: It is a colourless gas that is highly soluble in water. It has a boiling point of -85.05 °C and a melting point of -114.22 °C. Dry HCl gas is a poor conductor of electricity.
- Chemical Properties: In its aqueous solution (hydrochloric acid), it is a strong acid that reacts with metals, bases, and salts. It reacts with ammonia to form dense white fumes of ammonium chloride.
3. How is Hydrogen Chloride gas prepared in a laboratory setting?
In the laboratory, Hydrogen Chloride gas is typically prepared by heating sodium chloride (NaCl) with concentrated sulphuric acid (H₂SO₄). The reaction proceeds in two steps depending on the temperature, but the overall reaction below 200°C is:
NaCl + H₂SO₄ → NaHSO₄ + HCl(g)
The gas produced is then dried by passing it through concentrated sulphuric acid.
4. What are some important industrial applications of Hydrogen Chloride?
Hydrogen Chloride is a vital chemical in many industries. Its major applications include:
- Production of hydrochloric acid, a major industrial acid.
- Manufacturing of polymers like polyvinyl chloride (PVC) through the production of vinyl chloride.
- In the 'pickling' of steel to remove rust or iron oxide scale before processing.
- Used in the semiconductor industry to etch semiconductor crystals.
- Synthesis of other chemicals, including aqua regia (a mixture of nitric acid and hydrochloric acid).
5. Why is the Hydrogen Chloride (HCl) molecule considered polar?
The HCl molecule is polar due to the significant difference in electronegativity between the chlorine and hydrogen atoms. Chlorine is much more electronegative than hydrogen, causing it to pull the shared pair of electrons in the covalent bond closer to itself. This creates a partial negative charge (δ-) on the chlorine atom and a partial positive charge (δ+) on the hydrogen atom, resulting in a permanent dipole moment and making the molecule polar.
6. How does gaseous Hydrogen Chloride differ from its aqueous solution, Hydrochloric acid?
The primary difference lies in their chemical nature and behaviour. Gaseous HCl is a molecular compound with a covalent bond. In this state, it does not exhibit acidic properties. In contrast, Hydrochloric acid is the aqueous solution of HCl. When HCl gas dissolves in water, it ionises to form hydronium ions (H₃O⁺) and chloride ions (Cl⁻). The presence of these hydronium ions is what gives hydrochloric acid its strong acidic properties, such as turning blue litmus paper red.
7. What happens when a glass rod dipped in ammonia solution is brought near Hydrogen Chloride gas?
When a glass rod dipped in ammonia (NH₃) solution is brought near Hydrogen Chloride (HCl) gas, dense white fumes are immediately observed. This is a classic chemical test. The fumes are solid particles of ammonium chloride (NH₄Cl), formed by the direct combination of the two gases. The chemical equation for this reaction is:
NH₃(g) + HCl(g) → NH₄Cl(s)
8. Why is concentrated sulphuric acid used to dry HCl gas, and not calcium oxide?
Concentrated sulphuric acid (H₂SO₄) is used because it is an effective dehydrating agent and, being acidic itself, it does not react with the acidic HCl gas. On the other hand, a drying agent like calcium oxide (CaO) cannot be used. Calcium oxide is a basic oxide, and it would readily react with the acidic Hydrogen Chloride gas in a neutralization reaction to form calcium chloride and water, thus defeating the purpose of preparation.
CaO + 2HCl → CaCl₂ + H₂O
9. What are the major safety hazards associated with Hydrogen Chloride gas?
Hydrogen Chloride is a hazardous substance that requires careful handling. The primary safety concerns are:
- Corrosivity: It is highly corrosive. On contact with moisture, such as in the eyes, skin, or respiratory tract, it forms hydrochloric acid, causing severe chemical burns.
- Inhalation Hazard: Inhaling the gas can cause coughing, choking, and inflammation of the nose, throat, and upper respiratory tract. Severe exposure can lead to pulmonary edema and other critical conditions.
- Eye and Skin Damage: Direct contact can cause permanent eye damage and severe skin burns.
10. Can Hydrogen Chloride act as a reducing agent? Provide an example.
Yes, although it is not a strong reducing agent, HCl can act as one when it reacts with strong oxidizing agents. In such reactions, the chloride ion (Cl⁻), with an oxidation state of -1, is oxidized to chlorine gas (Cl₂), with an oxidation state of 0. A prominent example is the reaction of hydrochloric acid with manganese dioxide (MnO₂) to produce chlorine gas:
MnO₂(s) + 4HCl(aq) → MnCl₂(aq) + Cl₂(g) + 2H₂O(l)
