Hydrochloric acid
[CAS# 7647-01-0]

Identification

• Classification: Inorganic chemical industry >> Inorganic acid
• Name: Hydrochloric acid
• Synonyms: Hydrogen chloride
• Molecular Formula: HCl
• Molecular Weight: 36.46
• CAS Registry Number: 7647-01-0
• EC Number: 231-595-7
• SMILES: Cl

Properties

• Solubility: soluble (water, alcohol, ether, benzene)
• Density: 1.187 g/mL (-84.9 ºC) (Expl.)
• Melting point: -114 ºC (Expl.)
• Boiling point: 100 ºC (Expl.)
• Flash point: 10 ºC (Expl.)

Safety Data

• Hazard Symbols: GHS04;GHS06;GHS05;GHS07 Danger
• Hazard Statements: H280-H290-H314-H318-H331-H335
• Precautionary Statements: P234-P260-P261-P264-P264+P265-P271-P280-P301+P330+P331-P302+P361+P354-P304+P340-P305+P354+P338-P316-P317-P319-P321-P363-P390-P403+P233-P405-P406-P410+P403-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin corrosion	Skin Corr.	1B	H314
Skin corrosion	Skin Corr.	1A	H314
Acute toxicity	Acute Tox.	3	H331
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Serious eye damage	Eye Dam.	1	H318
Gases under pressure (liquid)	Press. Gas (Liq.)		H281
Gases under pressure (liquid)	Press. Gas (Liq.)		H280
Acute toxicity	Acute Tox.	4	H302
Acute toxicity	Acute Tox.	3	H311
Gases under pressure (compressed)	Press. Gas (Comp.)		H280
Acute toxicity	Acute Tox.	2	H330
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	4	H332
Eye irritation	Eye Irrit.	2	H319
Skin corrosion	Skin Corr.	1C	H314
Respiratory sensitization	Resp. Sens.	1	H334
Skin corrosion	Skin Corr.	1	H314
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Specific target organ toxicity - single exposure	STOT SE	1	H370
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Reproductive toxicity	Repr.	1B	H360
Acute toxicity	Acute Tox.	3	H332
Flammable liquids	Flam. Liq.	2	H225
Acute toxicity	Acute Tox.	3	H301
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Acute toxicity	Acute Tox.	2	H331
Reproductive toxicity	Repr.	1A	H360
Specific target organ toxicity - single exposure	STOT SE	2	H371

• Transport Information: UN 1789

Discovory and Applicatios

Hydrochloric acid (HCl) is a strong, corrosive acid that has been known and used for centuries. Its discovery dates back to the early alchemical traditions, where it was produced by reacting salt with sulfuric acid, a process that was refined over time. The industrial production of hydrochloric acid began in the 19th century, with the development of more efficient methods of manufacturing it, particularly through the chlorination of hydrocarbons.

Hydrochloric acid is a simple molecule composed of hydrogen and chlorine, and it is classified as a mineral acid. It is commonly found in a concentrated aqueous solution, where it dissociates completely into hydrogen ions (H⁺) and chloride ions (Cl⁻). In its concentrated form, hydrochloric acid is highly reactive and has numerous applications across various industries.

One of the most important industrial uses of hydrochloric acid is in metal cleaning and processing. It is widely used to remove rust, scale, and other impurities from metals through a process called pickling. The acid reacts with the oxide layers on the metal, dissolving them and restoring the metal's surface. Hydrochloric acid is also used in the production of certain metals, such as steel, and in the refining of petroleum.

In addition to its role in metal industries, hydrochloric acid is essential in the chemical synthesis of numerous compounds. It is used in the production of PVC (polyvinyl chloride), an important plastic used in construction, healthcare, and other sectors. It also plays a key role in the manufacturing of various pharmaceuticals, food additives, and cleaning products.

Hydrochloric acid is involved in many other industrial processes, such as the production of fertilizers, the extraction of certain metals from ores, and the refinement of oil and gas. It is also used in the preparation of various salts, including sodium chloride, potassium chloride, and ammonium chloride.

In the laboratory, hydrochloric acid is a common reagent used for acid-base reactions, pH adjustments, and titrations. It is often employed to prepare standard solutions, as its acidic properties make it a useful tool for a wide range of analytical techniques. Additionally, it is utilized in the production of hydrogen chloride gas, which is an important compound in the chemical industry.

Hydrochloric acid also has biological relevance. It is naturally present in the stomach, where it aids in digestion and helps maintain an acidic environment that is inhospitable to many pathogens. Its secretion is regulated by the stomach lining and is essential for proper digestion and absorption of nutrients.

Overall, hydrochloric acid is a versatile and essential chemical with a wide range of applications across various industries, from metal processing and chemical synthesis to food production and laboratory research. Its strong acidic properties and reactivity make it a valuable tool in both industrial and scientific settings.

References

2025. Weizmannia coagulans Extracellular Proteins Reduce Skin Acne by Inhibiting Pathogenic Bacteria and Regulating TLR2/TRAF6-Mediated NF-?B and MAPKs Signaling Pathways. Probiotics and Antimicrobial Proteins, 17(2).
DOI: 10.1007/s12602-023-10175-2

2025. Ce-doped TiO2 supported RuO2 as efficient catalysts for the oxidation of HCl to Cl2. Journal of environmental sciences (China), 149.
DOI: 10.1016/j.jes.2024.01.017

1835. Experiments and observations on the gastric juice and the physiology of digestion. The Dublin Journal of Medical and Chemical Science, 5(14).
DOI: 10.1007/bf02947358