Chemical Properties
Hydrochloric acid, or hydrogen chloride, is either a colorless liquid with a pungent odor,
or a colorless to slightly yellow gas that can be shipped as a liquefi ed compressed gas. The
acid is used in the production of fertilizers, dyes, dyestuffs, artifi cial silk, and paint pig-
ments, and in refi ning edible oils and fats. Hydrochloric acid is also used in electroplating,
leather tanning, ore refi ning, soap refi ning, petroleum extraction, and pickling of metals,
and is used in the photographic, textile, and rubber industries. In addition, hydrochloric
acid is used as an antiseptic in toilet bowls against animal pathogenic bacteria, and in food
processing as a starch modifi er.
Reactivity Profile
ANHYDROUS HYDROGEN CHLORIDE is an anhydrous (no water) strong acid. Reacts rapidly and exothermically with bases of all kinds (including amines and amides). Reacts exothermically with carbonates (including limestone and building materials containing limestone) and hydrogen carbonates to generate carbon dioxide. Reacts with sulfides, carbides, borides, and phosphides to generate toxic or flammable gases. Reacts with many metals (including aluminum, zinc, calcium, magnesium, iron, tin and all of the alkali metals) to generate flammable hydrogen gas. Reacts violently with acetic anhydride, 2-aminoethanol, ammonium hydroxide, calcium phosphide, chlorosulfonic acid, 1,1-difluoroethylene, ethylenediamine, ethyleneimine, oleum, perchloric acid, b-propiolactone, propylene oxide, silver perchlorate/carbon tetrachloride mixture, sodium hydroxide, uranium(IV) phosphide, vinyl acetate, calcium carbide, rubidium carbide, cesium acetylide, rubidium acetylide, magnesium boride, mercury(II) sulfate [Lewis]. Undergoes a very energetic reaction with calcium phosphide [Mellor 8:841(1946-1947)]. Corrosive to metals and tissues and irritating to the eyes and respiratory system. Corrodes galvanized or copper-alloy metals (brass, bronze); fittings of stainless steel or mild or cast steel must therefore be used. Reacts with calcium carbide with incandescence [Mellor 5:862(1946-1947]. Absorption on mercuric sulfate becomes violent at 125°C. [Mellor 2, Supp. 1:462(1956)].
Air & Water Reactions
Fumes strongly in moist air. Soluble in water with evolution of heat.
Hazard
Toxic by inhalation, strong irritant to eyes
and skin. Questionable carcinogen.
Health Hazard
Exposures to hydrochloric acid cause severe health effects and corrosive reactions.
Concentrated hydrochloric acid (fuming hydrochloric acid) forms acidic mists. Both the
mist and the solution have a corrosive effect on human tissue, with the potential to damage
the respiratory organs, eyes, skin, and intestines. Inhalation of vapors can cause coughing,
choking, infl ammation of the nose, throat, and upper respiratory tract, and in severe cases,
pulmonary edema, circulatory failure, and death. Accidental ingestion and/or swallow-
ing of hydrochloric acid at workplaces causes immediate pain and burns of the mouth,
throat, esophagus, and gastrointestinal tract. It also causes nausea, vomiting, and diar-
rhea, and in severe cases, death. Any kind of contact of the skin surfaces to hydrochloric
acid causes redness, pain, and severe skin burns. Concentrated solutions of hydrochloric
acid cause deep ulcers and discolor the skin. Vapors of hydrochloric acid cause irritat-
ing effects to the eyes and eye damage, leading to severe burns and permanent eye dam-
age. Long-term exposures to concentrated vapors of hydrochloric acid cause erosion of the
teeth. Occupational workers and persons with pre-existing skin disorders or eye disease
are more susceptible to the effects of hydrochloric acid.
Health Hazard
Gas concentrations of 50 to 100 ppm are tolerable for 1 hour. Concentrations of 1,000 to 2,000 ppm are dangerous, even for brief exposures. More severe exposures will result in serious respiratory distress and prolonged exposures will result in death. Mists of hydrochloric acid are considered less harmful than anhydrous hydrochloric acid, because droplets have no dehydrating action. Individuals with respiratory problems and digestive diseases may be adversely affected by low level exposures to the gas or mist.
Fire Hazard
Fire may produce irritating or poisonous gases. Containers may explode in heat of fire. At high temperatures, HYDROGEN CHLORIDE, ANHYDROUS decomposes into hydrogen and chlorine. The following materials should be avoided: Mercuric sulfate--violent reaction with gaseous hydrochloric acid at 250F. Sodium--reacts vigorously with gaseous hydrochloric acid. Acetic anhydride, 2-aminoethanol, ammonium hydroxide, chlorosulfonic acid, ethylene diamine, ethyleneimine, oleum, propiolactone, sodium hydroxide, sulfuric acid, and vinyl acetate--increase in temperature and pressure when mixed with hydrochloric acid. Calcium phosphide--energetic reaction with hydrochloric acid. Silver perchlorate and carbon tetrachloride--when mixed in combination with hydrochloric acid forms a compound that detonates at 105F. Formaldehyde--when mixed with hydrochloric acid forms a human carcinogen. Material reacts violently with bases and is corrosive with the generation of heat. Reacts with base metals, forming combustible gas (hydrogen). Reacts violently with strong oxidants forming toxic gas (chlorine). Avoid heat; at high temperatures HYDROGEN CHLORIDE, ANHYDROUS will decompose into hydrogen and chlorine.
Description
A water solution of hydrogen chloride of varied concentrations. It
is a clear, colorless or slightly yellowish, corrosive liquid having
a pungent odor. It is miscible with water and with alcohol. Concentrations of hydrochloric acid are expressed in percent by
weight, or may be expressed in Baume degrees (Be0) from
which percentages of hydrochloric acid and specific gravities may
readily be derived. The usually available concentrations are 18°,
20°, 22°, and 23° Be. Concentrations above 13° Be (19.6%) fume
in moist air, lose hydrogen chloride, and create a corrosive atmosphere. Because of these characteristics, suitable precautions must
be observed during sampling and analysis to prevent losses.
Note: Hydrochloric acid is produced by various methods that
might impart trace amounts of organic compounds as impurities.
The manufacturer, vendor, or user is responsible for identifying
the specific organic compounds that are present and for meeting
the requirements for organic compounds. Methods are provided
for their determination. In applying the procedures any necessary
standards should be used to quantitate the organic compounds
present in each specific product.
Physical properties
Colorless gas; sharp pungent odor; fumes in air; nonflammable; refractiveindex of gas at 0°C 1.000446; density of the gas 1.639 g/L (1.268 times heav-ier than air); density of liquid at -155°C 1.045 g/cm3; density of solid at-192°C 1.507 g/cm3; liquefies at -85.05°C to a colorless liquid; freezes to awhite crystalline solid at -114.22°C; critical temperature 51.55°C; criticalpressure 82.01 atm; critical volume 81 cm3/mol; triple point -114.25°C; dielec-tric constant at 25°C 1.0046; electrical conductivity 35.0 micromho/cm at-87.6°C; highly soluble in water 42.02 g/100 g solution (or 72.47 g/100 g water)at 20°C and 1 atm; soluble in alcohols and ethers (47.0 g and 24.9 g/100 g solu-tion at 20°C in methanol and ether, respectively.)
Hydrochloric acid is a colorless to yellowish liquid (the yellow colorationmay be due to traces of iron, chlorine or organics contaminants); fumes in air;refractive index of 1.0 N solution 1.3417; density of commercial concentratedacid (37.8 g/100g solution) 1.19 g/mL, and constant boiling solution (20.22g/100g solution) 1.096 g/mL at 25°C; forms a constant boiling azeotrope withwater at HCl concentration 20.22%; the azeotrope boils at 108.6°C; severalmetal chlorides can be salted out of their aqueous solutions by addition ofHCl; the addition of CaCl2can break the azeotrope; the pH of the acid at 1.0,0.1 and 0.01 N concentrations are 0.10, 1.1, and 2.02, respectively; a 10.0 Msolution ionizes to 92.6% at 18°C.
Definition
A colorless fuming liquid
made by adding hydrogen chloride to
water:
HCl(g) + H2O1. → H3O+(aq) + Cl-(aq)
Dissociation into ions is extensive and
hydrochloric acid shows the typical properties
of a strong acid. It reacts with carbonates
to give carbon dioxide and yields
hydrogen when reacted with all but the
most unreactive metals. Hydrochloric acid
is used in the manufacture of dyes, drugs,
and photographic materials. It is also used
to pickle metals, i.e. clean the surface prior
to electroplating. Hydrochloric acid donates
protons with ease and is the strongest
of the hydrohalic acids. The concentrated
acid is oxidized to chlorine by such agents
as potassium manganate(VII) and manganese(
IV) oxide.
Definition
ChEBI: A mononuclear parent hydride consisting of covalently bonded hydrogen and chlorine atoms.
Definition
hydrogen chloride: A colourlessfuming gas, HCl; m.p. –114.8°C; b.p.–85°C. It can be prepared in the laboratoryby heating sodium chloridewith concentrated sulphuric acid(hence the former name spirits ofsalt). Industrially it is made directlyfrom the elements at high temperatureand used in the manufacture ofPVC and other chloro compounds. Itis a strong acid and dissociates fullyin solution (hydrochloric acid).
Production Methods
Hydrochloric acid is an aqueous solution of hydrogen chloride gas
produced by a number of methods including: the reaction of sodium
chloride and sulfuric acid; the constituent elements; as a by-product
from the electrolysis of sodium hydroxide; and as a by-product
during the chlorination of hydrocarbons.
Production Methods
The traditional method of preparation of hydrochloric acid is the reaction of metal chlorides, especially sodium chloride with sulfuric acid (see the first reaction described). Hydrochloric acid is also produced by direct synthesis from its elements. In the chlorine-alkali industry, electrochemical reactions produce elemental chlorine and hydrogen, which can then be combined to give hydrogen chloride: Cl2(g) + H2(g) 2HCl(g). Hydrogen chloride is then dissolved in water to produce hydrochloric acid. By far, the most common method of producing hydrochloric acid involves its production as a by-product in chlorination reactions. This has curtailed this source of hydrochloric acid. The production of other common industrial organic chemicals such as Teflon, perchloroethylene, and polyvinyl chloride result in the production of hydrogen chloride. The production of hydrochloric acid in polyvinyl chloride production takes place when ethylene is chlorinated: C2H4(g) + Cl2(g) C2H4Cl2(g) C2H4Cl2(g)(g) C2H3Cl(g) + HCl(g).
Flammability and Explosibility
Noncombustible, but contact with metals may produce highly flammable hydrogen
gas.
Pharmaceutical Applications
Hydrochloric acid is widely used as an acidifying agent, in a variety
of pharmaceutical and food preparations. It may
also be used to prepare dilute hydrochloric acid, which in addition
to its use as an excipient has some therapeutic use, intravenously in
the management of metabolic alkalosis, and orally for the treatment
of achlorhydria.
Industrial uses
Hydrochloric acid (HCl) is a highly corrosive liquid, emitting a pungent odor and
fumes in moist air. Concentrated hydrochloric acid is one of the strongest acids and
thus any desired pH from 0 to 7 can be easily achieved with the required dosage.
Hydrochloric acid is seldom used in mineral flotation. The largest use is in hydrometallurgical
processes and the pickling of hot rolled steel. In some cases, hydrochloric
acid is used for decoating iron-stained mineral surfaces before flotation.
Industrial uses
Hydrochloric acid (HCl) is soluble in water andis a strong mineral acid made by the action ofsulfuric acid on common salt, or as a byproductof the chlorination of hydrocarbons such asbenzene.HCl is used to some extent in pickling of metal prior to porcelain enameling.
Materials Uses
Piping, valves, and other equipment used in
direct contact with anhydrous hydrogen chloride
should be of stainless steel or of cast or mild
steel. Carbon steel may be used in some components,
but only if their temperature is controlled
to remain below about 265°F (l29°C). In
the presence of moisture, however, hydrogen
chloride will corrode most metals. Teflon, Kel F
and Hastelloy will resist corrosion.
Smaller sized valves, such as those used on
cylinders, constructed of aluminum-siliconbronze
with Monel stems have had satisfactory
service experience due to frequent maintenance.
The satisfactory extension of these materials to
other applications should be confirmed by testing
prior to use.
Safety
When used diluted, at low concentration, hydrochloric acid is not
usually associated with any adverse effects. However, the concentrated
solution is corrosive and can cause severe damage on contact
with the eyes and skin, or if ingested.
LD50 (mouse, IP): 1.4 g/kg
LD50 (rabbit, oral): 0.9 g/kg
Potential Exposure
Hydrogen chloride itself is used in themanufacture of pharmaceutical hydrochlorides, chlorine, vinylchloride from acetylene; alkyl chlorides from olefins; arsenictrichloride from arsenic trioxide; in the chlorination of rubber;as a gaseous flux for babbitting operations; and in organic syn-thesis involving isomerization, polymerization, alkylation, andnitration reactions. The acid is used in the production of fertili-zers,dyes, dyestuffs, artificial silk, and paint pigments; inrefining edible oils and fats; in electroplating; leather tanning;ore refining; soap refining; petroleum extraction; pickling ofmetals; and in the photographic, textile, and rubber industries.It has been used as a choking/pulmonary agent.
Physiological effects
ACGIH recommends a Threshold Limit ValueCeiling
(TLV-C) of 5 ppm (7.5 mg/m3) for hydrogen
chloride. The TLV-C is the concentration
that should not be exceeded during any part
of the working exposure.
OSHA lists a Ceiling Value of 5 ppm (7
mg/m3) for hydrogen chloride. The Ceiling
Value is the exposure limit that shall not be exceeded
at any time during the working day. If
instantaneous monitoring is not feasible, then
the ceiling shall be assessed as a I5-minute
TWA exposure that shall not be exceeded at any
time during the working day [3].
First aid
If this chemical gets into the eyes, remove anycontact lenses at once and irri gate immediately for at least15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, includ-ing resuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medi-cal attention. If victim is conscious, administer water ormilk. Do not induce vomiting. Medical observation isrecommended for 24- -48 h after breathing overexposure, aspulmonary edema may be delayed. As first aid for pulmo-nary edema, a doctor or authorized paramedic may consideradministering a corticosteroid spray. If frostbite hasoccurred, seek medical attentionimmediately; do NOT rubthe affected areas or flush them with water. In order to pre-vent further tissue damage, do NOT attempt to remove fro-zen clothing from frostbitten areas. If frostbite has NOToccurred, immediately and thoroughly wash contaminatedskin with soap and water.
storage
Hydrochloric acid should be stored in a well-closed, glass or other
inert container at a temperature below 30°C. Storage in close
proximity to concentrated alkalis, metals, and cyanides should be
avoided.
storage
Splash goggles and rubber gloves should be
worn when handling this acid, and containers of HCl should be stored in a wellventilated
location separated from incompatible metals. Water should never be added
to HCl because splattering may result; always add acid to water. Containers of
hydrochloric acid should be stored in secondary plastic trays to avoid corrosion of
metal storage shelves due to drips or spills.
Cylinders of hydrogen chloride
should be stored in cool, dry locations separated from alkali metals and other
incompatible substances.
Shipping
Anhydrous hydrogen chloride requires a shippinglabel of“POISON GAS, CORROSIVE." It falls in HazardClass 2.3. It is a violation of transportation regulations torefill compressed gas cylinders without the express writtenpermission of the owner. Hydrogen chloride, refrigeratedliquid, requires a shipping label of“POISON GAS,CORROSIVE.”It falls in Hazard Class 8. Hydrochloricacid requires a shipping label of“CORROSIVE." It falls in Hazard Class 8 and Packing Group I. Procedures for thehandling, use, and storage of cylinders should be in compli-ance with OSHA 1910.101 and 1910.169 with the recom-mendations of the Compressed Gas Association.Special precautions: Cylinders must be transported in asecure upright position, in a well-ventilated truck.
Purification Methods
Pass it through conc H2SO4, then over activated charcoal and silica gel. It fumes in moist air. Hydrogen chloride in gas cylinders contains ethylene, 1,1-dichloroethane and ethyl chloride. The latter two may be removed by fractionating the HCl through a trap cooled to -112o. Ethylene is difficult to remove. HCl fumes in moist air. HARMFUL VAPOURS. Its solubility in H2O is 82% at 0o. A constant boiling aqueous solution (azeotrope) has b 108.6o/760mm with an HCl concentration of ~20%, and is called Hydrochloric acid (muriatic acid) (see above). [Schmeisser in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 280-282 1963.]
Toxicity evaluation
HCl causes local pH changes and denatures proteins. This leads
to edema formation and tissue necrosis. HCl produces a coagulation
necrosis characterized by the formation of a scar.
Ingested HCl may give rise to damage of the esophagus and
stomach. Gastric damage may occur secondary to pooling of
HCl in the antrum as a result of pylorospasm. Patients who
survive ingestions of HCl may develop stricture formation,
gastric atony, and gastric outlet obstruction. When inhaled,
HCl typically deposits in the upper respiratory tract and causes
damage. Concentrated HCl can penetrate to the level of the
bronchioles and alveoli and cause subsequent damage to these
regions.
Incompatibilities
Hydrochloric acid and hydrogen chloride react violently with many metals, with the
generation of highly flammable hydrogen gas, which may explode. Reaction with
oxidizers such as permanganates, chlorates, chlorites, and hypochlorites may produce
chlorine or bromine.
Incompatibilities
Hydrochloric acid reacts violently with alkalis, with the evolution of
a large amount of heat. Hydrochloric acid also reacts with many
metals, liberating hydrogen.
Waste Disposal
In many localities, hydrochloric acid or the residue from a spill may be disposed of
down the drain after appropriate dilution and neutralization. Otherwise, hydrochloric
acid and waste material containing this substance should be placed in an appropriate
container, clearly labeled, and handled according to your institution's waste disposal
guidelines. Excess hydrogen chloride in cylinders should be returned to the
manufacturer. For more information on disposal procedures, see Chapter 7 of this
volume.
Regulatory Status
GRAS listed. Accepted for use as a food additive in Europe.
Included in the FDA Inactive Ingredients Database (dental
solutions; epidural injections; IM, IV, and SC injections; inhalations;
ophthalmic preparations; oral solutions; nasal, otic, rectal, and
topical preparations). Included in parenteral and nonparenteral
medicines licensed in the UK. Included in the Canadian List of
Acceptable Non-medicinal Ingredients.
GRADES AVAILABLE
Anhydrous hydrogen chloride is typically available
for commercial and industrial purposes in a
technical grade (minimum purity of 99.0 percent).
