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Hydrochroric Acid

Hydrochloric Acid

Gist

Hydrochloric acid (HCl) is an aqueous solution of hydrogen chloride, a strong, corrosive inorganic acid that is colorless, has a strong odor, and is found naturally in stomach gastric acid. Its uses include industrial processes like fertilizer, dye, and chloride production, electroplating, and textile manufacturing, as well as in household cleaners, but it is dangerous if ingested, inhaled, or exposed to skin. 

Hydrochloric acid is used in steel pickling, the food industry (like making corn syrup and acidifying canned goods), ore processing to extract metals, producing chlorides and plastics, and cleaning surfaces like toilets and tiles. It's a vital industrial chemical, also found in the digestive system to break down food and used in laboratories for chemical tests and titrations. 

Summary

Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digestive systems of most animal species, including humans. Hydrochloric acid is an important laboratory reagent and industrial chemical.

Chemical properties

Gaseous hydrogen chloride is a molecular compound with a covalent bond between the hydrogen and chlorine atoms. In aqueous solutions dissociation is complete, with the formation of chloride ions and hydrated hydrogen ions (hydronium ions). A combined IR, Raman, X-ray, and neutron diffraction study of concentrated hydrochloric acid showed that the hydronium ion forms hydrogen bonded complexes with other water molecules.

The pKa value of hydrochloric acid in aqueous solution is estimated theoretically to be −5.9. A solution of hydrogen chloride in water behaves as a strong acid: the concentration of HCl molecules is effectively zero.

Physical Properties

Physical properties of hydrochloric acid, such as boiling and melting points, density, and pH, depend on the concentration or molarity of HCl in the aqueous solution. They range from those of water at very low concentrations approaching 0% HCl to values for fuming hydrochloric acid at over 40% HCl.

Hydrochloric acid as the binary (two-component) mixture of HCl and H2O has a constant-boiling azeotrope at 20.2% HCl and 108.6 °C (381.8 K; 227.5 °F). There are four constant-crystallization eutectic points for hydrochloric acid, between the crystal form of [H3O]Cl (68% HCl), [H5O2]Cl (51% HCl), [H7O3]Cl (41% HCl), [H3O]Cl·5H2O (25% HCl), and ice (0% HCl). There is also a metastable eutectic point at 24.8% between ice and the [H7O3]Cl crystallization. They are all hydronium salts.

Details:

Hydrochloric acid is the aqueous solution of hydrogen chloride gas and the main component of gastric acid, an acid produced naturally in the human stomach to help digest food. Hydrochloric acid is synthetically produced for a variety of industrial and commercial applications.

Key Points/Overview

Hydrochloric acid can be used to process steel for the building and construction industry. It is used in the chemical industry in the large-scale production of vinyl chloride used to make PVC, and it is one of the chemicals used to produce polyurethane foam and calcium chloride.

Common end uses for hydrochloric acid include household cleaners, pool maintenance and food manufacturing.

OSHA recommends workers in industrial settings wear personal protective equipment such as vapor respirators, rubber gloves, splash goggles and face shields when handling hydrochloric acid.

Plastic containers, such as those made of PVC, can typically be used to store hydrochloric acid. Metal containers are generally not suitable for storing hydrochloric acid due to its corrosive nature.

Uses & Benefits

Hydrochloric acid is a strong, corrosive acid that can be used industrially to process steel used in the building and construction industry. It is used in the chemical industry in the large-scale production of vinyl chloride used to make polyvinyl chloride (PVC) plastic, and it is one of the chemicals that is used to produce polyurethane foam and calcium chloride.

Hydrochloric acid is also used to make many other chemicals and as a disinfectant and slimicide, a chemical that prevents the growth of slime in paper stock.

Other common end uses for hydrochloric acid include household cleaners, pool maintenance and food manufacturing.

Steel Production

Hydrochloric acid is used in pickling operations to remove rust and other impurities from carbon, alloy and stainless steel, to prepare the steel for final applications in building and construction projects, and in products such as car bodies and household appliances. It is also used in aluminum etching and metal cleaning applications.

Household Cleaners

Hydrochloric acid can be an ingredient in household cleaners such as toilet bowl cleaners, bathroom tile cleaners and other porcelain cleaners, due to its corrosive properties that help clean tough stains.

Pool Sanitation

Hydrochloric acid is used as a swimming pool treatment chemical, to help maintain an optimal pH in the water.

Food Production and Processing

The food industry uses hydrochloric acid to process a variety of food products, such as corn syrups used in soft drinks, cookies, crackers, ketchup and cereals. Hydrochloric acid is also used as an acidifier in sauces, vegetable juices and canned goods, to help enhance flavor and reduce spoilage.

Calcium Chloride Production

When hydrochloric acid is mixed or reacted with limestone, it produces calcium chloride, a type of salt used to de-ice roads. Calcium chloride also has uses in food production as a stabilizer and firming agent, for example in baked goods, as well as uses as an antimicrobial.

Additional Uses

Hydrochloric acid is used in the production of batteries, photoflash bulbs and fireworks. It is also used in leather processing, building and construction, oil well acidizing and producing gelatin products.

Safety Information

Hydrochloric acid in its concentrated, liquid form has a strong irritating odor and is very corrosive. It can cause damage, such as chemical burns, upon contact, according to the U.S. National Library of Medicine. The U.S. Centers for Disease Control and Prevention (CDC) notes that hydrochloric acid can cause eye damage, even blindness, if splashed in the eyes.

Ingestion of concentrated hydrochloric acid can cause severe injury to the mouth, throat, esophagus and stomach. Personal protective equipment (PPE) such as vapor respirators, rubber gloves, splash goggles and face shields should be used when handling hydrochloric acid. If used in the workplace, it is recommended that an eye flush station be available in case of accidental exposure.

When using pool cleaners that contain hydrochloric acid (also known as muriatic acid), it is important to follow directions on the product label for safe handling. The CDC has developed two posters with recommendations for pool chemical safety handling as well as storage of pool chemicals for pool owners and operators.

Storing Hydrochloric Acid

Metal containers are not suitable storage containers for hydrochloric acid due to its corrosive nature. Plastic containers, such as those made of PVC, can typically be used to store hydrochloric acid.

Additional Information

Hydrogen chloride (HCl) is a a compound of the elements hydrogen and chlorine, a gas at room temperature and pressure. A solution of the gas in water is called hydrochloric acid.

Hydrogen chloride may be formed by the direct combination of chlorine (Cl2) gas and hydrogen (H2) gas; the reaction is rapid at temperatures above 250 °C (482 °F). The reaction, represented by the equation H2 + Cl2 → 2HCl, is accompanied by evolution of heat and appears to be accelerated by moisture. Hydrogen chloride is commonly prepared both on a laboratory and on an industrial scale by the reaction of a chloride, generally that of sodium (NaCl), with sulfuric acid (H2SO4). It is also produced by the reaction of some chlorides (e.g., phosphorus trichloride, PCl3, or thionyl chloride, SOCl2) with water and as a by-product of the chlorination of many organic substances (e.g., methane or benzene).

Hydrochloric acid is prepared by dissolving gaseous hydrogen chloride in water. Because of the corrosive nature of the acid, ceramic, glass, or sometimes tantalum apparatus is commonly used. Hydrochloric acid is usually marketed as a solution containing 28–35 percent by weight hydrogen chloride, commonly known as concentrated hydrochloric acid. Anhydrous liquid hydrogen chloride is available, but because heavy and expensive containers are required to store it, the use of hydrogen chloride in this form is limited.

Hydrogen chloride is a colourless gas of strong odour. It condenses at −85 °C (−121 °F) and freezes at −114 °C (−173 °F). The gas is very soluble in water: at 20 °C (68 °F) water will dissolve 477 times its own volume of hydrogen chloride. Because of its great solubility, the gas fumes in moist air. A water solution containing 20.24 percent by weight hydrogen chloride boils at 110 °C (230 °F) without change in composition (azeotropic mixture). In aqueous solution the compound is extensively dissociated into a hydronium ion (H3O+) and chloride ion (Cl−); in dilute solutions the dissociation is essentially complete. Thus, hydrochloric acid is a strong acid.

Gaseous hydrogen chloride reacts with active metals and their oxides, hydroxides, and carbonates to produce chlorides. These reactions occur readily only in the presence of moisture. Completely dry hydrogen chloride is very unreactive. The reactions of hydrochloric acid are those of typical strong acids, such as: reactions with metals in which hydrogen gas is displaced, reactions with basic (metal) oxides and hydroxides that are neutralized with the formation of a metal chloride and water, and reactions with salts of weak acids in which the weak acid is displaced. Hydrochloric acid also enters into chemical reactions characteristic of the chloride ion, such as reactions with various inorganic and organic compounds in which hydrochloric acid is used as a chlorinating agent and reactions with metals and their oxides in which complex chloride-containing ions are formed (e.g., with platinum, [PtCl6]2−, or with copper, [CuCl4]2−). The latter type of reaction accounts for the ease of solution of certain metals and metallic compounds in hydrochloric acid although they are slowly dissolved in other acids of equal strength (e.g., sulfuric or nitric acid). For this reason, hydrochloric acid is used extensively in the industrial processing of metals and in the concentration of some ores.

Hydrochloric acid is present in the digestive juices of the human stomach. Excessive secretion of the acid causes gastric ulcers, while a marked deficiency of it impairs the digestive process and is sometimes the primary cause of deficiency anemias. Exposure to 0.1 percent by volume hydrogen chloride gas in the atmosphere may cause death in a few minutes. Concentrated hydrochloric acid causes burns and inflammation of the skin.

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