Hydrochloric acid

• BPHydrochloric Acid
• JPHydrochloric Acid
• Ph. Eur.Hydrochloric Acid, Concentrated
• USP–NFHydrochloric Acid

Chlorhydric acid; hydrogen chloride solution; muriatic acid; spirits of salt; E507

Hydrochloric acid (aqueous solution of hydrogen chloride) · [7647-01-0]

UNII QTT17582CB · PubChem CID 313

HCl · 36.46

pH adjuster, buffering agent

Typical concentrations: — · Dosage forms: Liquid, Sterile (parenteral/ophthalmic)

Used, usually after dilution, as an acidifying agent to adjust the pH of injections, ophthalmic, nasal, oral and topical products, and to form hydrochloride salts of basic drugs in situ. It is also used in analytical work and in the manufacture of other materials, and as a food acidulant.

Concentrated hydrochloric acid is a clear, colourless, fuming liquid with a pungent, irritating odour; Ph. Eur. and USP–NF specify about 35–39% w/w HCl. Dilute hydrochloric acid (about 10% HCl) is also official and does not fume.

Content

concentrated acid ≈ 35–39% w/w HCl; dilute acid ≈ 10% HCl

Density

≈ 1.18 g/cm³ (concentrated acid at 20 °C)

Acidity

strong mineral acid, completely dissociated in water

Solubility

miscible with water and ethanol

Concentrated acid loses hydrogen chloride gas on exposure to air. Store in tightly closed glass or other inert containers in a cool, well-ventilated place, away from metals and alkalis.

Reacts violently with alkalis. Attacks many metals with liberation of flammable hydrogen. With oxidising agents such as hypochlorites or permanganates it releases chlorine, and with formaldehyde it can form the carcinogen bis(chloromethyl) ether. Acid-labile drugs and excipients are hydrolysed.

Made by dissolving hydrogen chloride gas in water. The gas is obtained by direct combination of hydrogen and chlorine, as a by-product of the chlorination of organic compounds, or from sodium chloride and sulfuric acid.

Concentrated hydrochloric acid is corrosive and causes severe burns to skin, eyes and mucous membranes; its vapour irritates the respiratory tract. At the low levels used to adjust pH in medicines it presents no hazard, and dilute hydrochloric acid is a normal constituent of gastric juice.

Handle with great care. Wear acid-resistant gloves, goggles and a face shield, and work in a fume cupboard. Always add acid to water, never water to acid. Spills should be neutralised with sodium bicarbonate or another weak base.

GRAS listed. Accepted as a food additive in Europe (E507). Included in the FDA Inactive Ingredient Database (injectable, inhalation, nasal, ophthalmic, oral, otic and topical preparations) and in parenteral and non-parenteral medicines licensed in Europe.

Dilute hydrochloric acid; sodium hydroxide (for pH adjustment in the opposite direction); phosphoric acid; sulfuric acid.

For pH adjustment, dilute (for example 1 M or 10%) acid is normally used and added in small portions with mixing to avoid local overshoot. The amount added 'q.s. to pH' should be recorded, since it contributes chloride ions that can affect the solubility of hydrochloride salts by the common-ion effect.