What is Hydrochloric Acid?

Hydrochloric Acid - Overview

Hydrochloric acid is a strongly acidic, colourless, and viscous liquid with a distinctively pungent smell. Its distinct smell makes it easy to recognize in laboratories. HCl is used in leather processing and gelatin production. Most of the physical properties of HCl, like density, pH, melting point, and boiling point, depend on its molar concentration.

Properties of Hydrochloric Acid

• Molecular Weight/ Molar Mass: 36.458 g/mol
• Odour: Pungent smell
• Appearance: Transparent liquid
• Boiling Point: Concentration-dependent
• Melting Point: Concentration-dependent

Chemical Properties of Hydrochloric Acid

Gaseous hydrogen chloride readily forms chlorides with active metals, their carbonates, oxides, and hydroxides. The reactions mostly take place in the presence of humidity. It reacts with metals and displaces hydrogen gas. On reacting with simple (metal) oxides and hydroxides, it forms metal chloride and water – the common neutralisation reaction.

HCl Oxidation

HCl reacts with potassium permanganate or potassium dichromate to liberate chlorine gas.

2KMnO4 + 16 HCl → 2 KCl + 2 MnCl2 + 5 Cl2 + 8 H2O

2K2Cr2O7 + 14 HCl → 2 KCl + 2 CrCl3 + 3 Cl2 + 7 H2O

Reaction With Carbonates

Hydrochloric acid reacts with carbonates to produce carbon dioxide.

Na2CO3 + 2 HCl → 2 NaCl + H2O + CO2

Reaction With Bicarbonates

Hydrochloric acid reacts with hydrogen carbonates to give carbon dioxide.

NaHCO3 + HCl → NaCl + H2O + CO2

Reaction with Sulphites

Hydrochloric acid reacts with sulphites to give sulphur dioxide gas.

Na2SO3 + 2 HCl → 2 NaCl + H2O + SO2

Aqua Regia Formation

When concentrated hydrochloric acid and concentrated HNO3 combine in a 3:1 ratio, aqua regia is formed. This mixture can dissolve metals such as platinum and gold to form their respective chlorides.

Dissociation of HCl

HCl is a strong acid. According to Arrhenius, an acid is a substance that forms hydrogen ions or protons upon dissociation. The ease and quantity of hydrogen ion liberation make the acid strong or weak. HCl is categorized as a very strong acid because it dissociates in water. As a proton donor, HCl satisfies all the characteristics of an acid. It serves as a base only when it is a proton recipient, and that happens when it reacts with a higher acid dissociation constant substance or a superacid. The dissociation reaction is shown in the following equation:

HCl + H2O → H3O+ + Cl−

Hydrochloric Acid Uses

Earlier, it was dissolved in liquids and dumped in oceans as its industrial uses weren’t released. Later, with the advancement of scientific study, major uses of industrial uses came forward, including:

• Production of Organic Compounds: It is used in the production of organic compounds such as dichloromethane, vinyl chloride, plastics, bisphenol A, and more.
• Production of Inorganic Compounds: It is useful in preparing compounds used for water treatment, such as poly aluminium chloride (PAC), aluminium carbohydrate, and iron(III) chloride.
• For Table Salt Purification: HCl is popular for purifying table salts and regulating the acidity (pH) of solutions.
• Removing Metal Stains: It is used to remove rust or stains from metals like iron, copper, and more.
• Oil Production: HCl is used in oil production to form large-pore structures in rocks, aiding the extraction of oil.
• Other Uses: Making glue and gelatin, producing glucose, manufacturing plastics and synthetic rubber, refining cane sugar, manufacturing aqua regia for dissolving gold and platinum, chloride production, and in the textile industry for dye manufacturing.

Hydrochloric Acid in the Human Body

Hydrochloric acid is naturally found in the human body, produced by abdominal parietal cells. The secretion of the stomach comprises various enzymes and hydrochloric acid, which helps in food breakdown, digestion, and killing bacteria and viruses. The concentration of hydrochloric acid in the stomach is around 0.5%, and its pH is about 1.0-2.0, making it an important defense against microbial infections.

Hydrochloric Acid on Skin

The hydrochloric acid present in the stomach is mild, but the laboratory-grade hydrochloric acid is strong and can cause harm. If you get hydrochloric acid on your skin, immediately take the following steps:

• Rinse the affected area thoroughly with clean water.
• Do not rub the area and allow water to run off rather than pool on the skin.

Hydrochloric Acid Safety

If you swallow hydrochloric acid, seek medical attention immediately and avoid inducing vomiting unless advised. In the case of skin contact, remove contaminated clothing, wash the area with soap and water, and seek medical advice if symptoms persist.

Conclusion

Hydrochloric acid is a corrosive but useful chemical that plays an important role in industrial and biological processes. It is used in various industries, such as plastic manufacturing, oil production, and metal cleaning. In the human body, it aids digestion and helps protect against infections.

Frequently Asked Questions

• What is the most popular use of hydrochloric acid? It is used in manufacturing plastics, cleaning, and descaling. It also plays a role in gelatin processing and is a food additive.
• How would you neutralize hydrochloric acid? You can neutralize hydrochloric acid using a strong base like sodium bicarbonate or baking soda. Apply it before it begins to fizz and then flush with water.
• Is hydrochloric acid weak or strong? Hydrochloric acid is a strong acid because it dissociates completely in water.
• What is Hydrochloride? Hydrochloride is the product obtained when hydrochloric acid reacts with an organic base, such as pyridine, methylamine, or benzimidazole.