Everything about Hydrochloric Acid totally explained
| Section2 =
| Section7 =,
| SPhrases =,,
}}
| Section8 =
}}
Hydrochloric acid is the
aqueous solution of
hydrogen chloride gas (
HCl). It is a
strong acid, and the major component of
gastric acid. It is also widely used in industry. Hydrochloric acid must be handled with appropriate
safety precautions because it's a highly
corrosive solution.
Hydrochloric acid, or
Muriatic acid by its historical but still occasionally used name, has been an important and frequently-used chemical from early history, and was discovered by the
alchemist Jabir ibn Hayyan around the year 800. It was used throughout the
Middle Ages by alchemists in the quest for the
philosopher's stone, and later by several European
scientists including
Glauber,
Priestley, and
Davy in order to help establish modern chemical knowledge.
From the
Industrial Revolution, it became a very important industrial chemical for many applications, including the large-scale production of
organic compounds, such as
vinyl chloride for
PVC plastic, and
MDI/
TDI for
polyurethane, and smaller-scale applications, such as production of
gelatin and other
ingredients in food, and
leather processing. About 20 million metric tonnes of HCl gas are produced annually.
History
Hydrochloric acid was first discovered around 800 AD by the
alchemist Jabir ibn Hayyan (Geber), by mixing
common salt with
vitriol (
sulfuric acid). Jabir discovered many important chemicals, and recorded his findings in over twenty books, which carried his chemical knowledge of hydrochloric acid and other basic chemicals for hundreds of years. Jabir's invention of the gold-dissolving
aqua regia, consisting of hydrochloric acid and
nitric acid, was of great interest to alchemists searching for the
philosopher's stone.
In the
Middle Ages, hydrochloric acid was known to European alchemists as
spirits of salt or
acidum salis. It is still known as "Spirits of Salt" when sold for domestic cleaning purposes in the United Kingdom today. Gaseous HCl was called
marine acid air. The old (pre-
systematic) name
muriatic acid has the same origin (
muriatic means "pertaining to brine or salt"), and this name is still sometimes used. Notable production was recorded by
Basilius Valentinus, the alchemist-
canon of the
Benedictine priory Sankt Peter in
Erfurt, Germany in the fifteenth century. In the seventeenth century,
Johann Rudolf Glauber from
Karlstadt am Main, Germany used sodium chloride salt and sulfuric acid for the preparation of
sodium sulfate in the
Mannheim process, releasing
hydrogen chloride gas.
Joseph Priestley of
Leeds, England prepared pure hydrogen chloride in 1772, and in 1818
Humphry Davy of
Penzance, England proved that the chemical composition included
hydrogen and
chlorine.
During the
Industrial Revolution in Europe, demand for
alkaline substances such as
soda ash increased, and the new industrial soda process by
Nicolas Leblanc (
Issoundun, France) enabled cheap large-scale production. In the
Leblanc process, salt is converted to soda ash, using sulfuric acid, limestone, and coal, releasing hydrogen chloride as a by-product. Until the
Alkali Act of 1863, excess HCl was vented to the air. After the passage of the act, soda ash producers were obliged to absorb the waste gas in water, producing hydrochloric acid on an industrial scale.
When early in the twentieth century the Leblanc process was effectively replaced by the
Solvay process without the hydrochloric acid by-product, hydrochloric acid was already fully settled as an important chemical in numerous applications. The commercial interest initiated other production methods which are still used today, as described below. Today, most hydrochloric acid is made by absorbing hydrogen chloride from
industrial organic compounds production.
Hydrochloric acid is listed as a Table II precursor under the 1988
United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances because of its use in the production of
heroin,
cocaine, and
methamphetamine.
Chemistry
Hydrogen chloride (HCl) is a
monoprotic acid, which means it can
dissociate (
for example, ionize) only once to give up one H
+ ion (a single
proton). In aqueous hydrochloric acid, the H
+ joins a water molecule to form a
hydronium ion, H
3O
+:
» : HCl + H
2O ⇌ H
3O
+ + Cl
−
The other ion formed is Cl
−, the
chloride ion. Hydrochloric acid can therefore be used to prepare salts called
chlorides, such as
sodium chloride. Hydrochloric acid is a
strong acid, since it's fully dissociated in water.
Monoprotic acids have one
acid dissociation constant, K
a, which indicates the level of dissociation in water. For a strong acid like HCl, the K
a is large. Theoretical attempts to assign a K
a to HCl have been made. When chloride salts such as NaCl are added to aqueous HCl they've practically no effect on
pH, indicating that Cl
− is an exceedingly weak
conjugate base and that HCl is fully dissociated in aqueous solution. For intermediate to strong solutions of hydrochloric acid, the assumption that H
+ molarity (a unit of
concentration) equals HCl molarity is excellent, agreeing to four significant digits.
Of the seven common strong acids in chemistry, all of them
inorganic, hydrochloric acid is the monoprotic acid least likely to undergo an interfering
oxidation-reduction reaction. It is one of the least hazardous strong acids to handle; despite its acidity, it produces the less reactive and non-toxic chloride ion. Intermediate strength hydrochloric acid solutions are quite stable, maintaining their concentrations over time. These attributes, plus the fact that it's available as a pure
reagent, mean that hydrochloric acid makes an excellent acidifying reagent and acid titrant (for determining the amount of an unknown quantity of
base in
titration). Strong acid titrants are useful because they give more distinct endpoints in a titration, making the titration more precise. Hydrochloric acid is frequently used in
chemical analysis and to digest samples for analysis. Concentrated hydrochloric acid will dissolve some
metals to form oxidized metal chlorides and
hydrogen gas. It will produce metal chlorides from basic compounds such as
calcium carbonate or
copper(II) oxide. It is also used as a simple acid
catalyst for some
chemical reactions.
Physical Properties
The
physical properties of hydrochloric acid, such as
boiling and
melting points,
density, and
pH depend on the
concentration or
molarity of HCl in the acid solution. They can range from those of water at 0% HCl to values for fuming hydrochloric acid at over 40% HCl.
Conc. (w/w)
c : kg HCl/kg |
Conc. (w/v)
c : kg HCl/m3 |
Conc.
Baumé
|
Density
ρ : kg/l |
Molarity
M |
pH
|
Viscosity
η : mPa·s |
Specific
heat
s : kJ/(kg·K) |
Vapor
pressure
PHCl : Pa |
Boiling
point
b.p. |
Melting
point
m.p. |
| 10% |
104.80 |
6.6 |
1.048 |
2.87 M |
-0.5 |
1.16 |
3.47 |
0.527 |
103 °C |
-18 °C |
| 20% |
219.60 |
13 |
1.098 |
6.02 M |
-0.8 |
1.37 |
2.99 |
27.3 |
108 °C |
-59 °C |
| 30% |
344.70 |
19 |
1.149 |
9.45 M |
-1.0 |
1.70 |
2.60 |
1,410 |
90 °C |
-52 °C |
| 32% |
370.88 |
20 |
1.159 |
10.17 M |
-1.0 |
1.80 |
2.55 |
3,130 |
84 °C |
-43 °C |
| 34% |
397.46 |
21 |
1.169 |
10.90 M |
-1.0 |
1.90 |
2.50 |
6,733 |
71 °C |
-36 °C |
| 36% |
424.44 |
22 |
1.179 |
11.64 M |
-1.1 |
1.99 |
2.46 |
14,100 |
61 °C |
-30 °C |
| 38% |
451.82 |
23 |
1.189 |
12.39 M |
-1.1 |
2.10 |
2.43 |
28,000 |
48 °C |
-26 °C |
The reference temperature and pressure for the above table are 20 °C and 1 atmosphere (101 kPa).
Hydrochloric acid as the binary (two-component) mixture of HCl and H
2O has a constant-boiling
azeotrope at 20.2% HCl and 108.6 °C (227 °F). There are four constant-
crystallization eutectic points for hydrochloric acid, between the
crystal form of HCl·H
2O (68% HCl), HCl·2H
2O (51% HCl), HCl·3H
2O (41% HCl), HCl·6H
2O (25% HCl), and
ice (0% HCl). There is also a metastable eutectic point at 24.8% between ice and the HCl·3H
2O crystallization
Production
Hydrochloric acid is prepared by dissolving hydrogen chloride in water. Hydrogen chloride can be generated in many ways, and thus several precursors to hydrochloric acid exist. The large-scale
production of hydrochloric acid is almost always integrated with other industrial scale
chemicals production.
Industrial market
Hydrochloric acid is produced in solutions up to 38% HCl (concentrated grade). Higher
concentrations up to just over 40% are chemically possible, but the
evaporation rate is then so high that
storage and handling need extra precautions, such as
pressure and low
temperature. Bulk industrial-grade is therefore 30% to 34%, optimized for effective
transport and limited product loss by HCl
vapors. Solutions for household purposes in the US, mostly cleaning, are typically 10% to 12%, with strong recommendations to dilute before use. In the United Kingdom where it's sold as "Spirits of Salt" for domestic cleaning, the potency is the same as the US industrial grade.
Major producers worldwide include
Dow Chemical at 2 million metric tonnes annually (2 Mt/year), calculated as HCl gas, and
FMC,
Georgia Gulf Corporation,
Tosoh Corporation,
Akzo Nobel, and
Tessenderlo at 0.5 to 1.5 Mt/year each. Total world production, for comparison purposes expressed as HCl, is estimated at 20 Mt/year, with 3 Mt/year from direct synthesis, and the rest as secondary product from organic and similar syntheses. By far, most of all hydrochloric acid is consumed captively by the producer. The open world market size is estimated at 5 Mt/year.
Applications
Hydrochloric acid is a strong inorganic acid that's used in many industrial processes. The application often determines the required product quality.
Regeneration of ion exchangers
An important application of high-quality hydrochloric acid is the regeneration of
ion exchange resins.
Cation exchange is widely used to remove
ions such as Na
+ and Ca
2+ from
aqueous solutions, producing
demineralized water.
» : Na
+ is replaced by H
3O
+
: Ca
2+ is replaced by 2 H
3O
+
Ion exchangers and demineralized water are used in all chemical industries,
drinking water production, and many
food industries.
pH Control and neutralization
A very common application of hydrochloric acid is to regulate the
basicity (
pH) of solutions.
» : OH
− + HCl → H
2O + Cl
−
In industry demanding purity (food, pharmaceutical, drinking water), high-quality hydrochloric acid is used to control the pH of process water streams. In less-demanding industry, technical-quality hydrochloric acid suffices for
neutralizing waste streams and
swimming pool treatment.
Pickling of steel
Pickling is an essential step in
metal surface treatment, to remove
rust or
iron oxide scale from
iron or
steel before subsequent processing, such as
extrusion,
rolling,
galvanizing, and other techniques. Technical-quality HCl at typically 18% concentration is the most commonly-used pickling agent for the pickling of
carbon steel grades.
» : Fe
2O
3 + Fe + 6 HCl → 3 FeCl
2 + 3 H
2O
The
spent acid has long been re-used as
ferrous chloride solutions, but high
heavy-metal levels in the pickling liquor has decreased this practice.
In recent years, the steel pickling industry has, however, developed
hydrochloric acid regeneration processes, such as the spray roaster or the fluidized bed HCl regeneration process, which allow the recovery of HCl from spent pickling liquor. The most common regeneration process is the pyrohydrolysis process, applying the following formula:
» : 4 FeCl
2 + 4 H
2O + O
2 → 8 HCl+ 2 Fe
2O
3
By recuperation of the spent acid, a closed acid loop is established. The ferric oxide by product of the regeneration process is a valuable by-product, used in a variety of secondary industries.
HCl isn't a common pickling agent for
stainless steel grades.
Production of inorganic compounds
Numerous products can be produced with hydrochloric acid in normal
acid-base reactions, resulting in
inorganic compounds. These include water treatment chemicals such as
iron(III) chloride and
polyaluminium chloride (PAC).
» : Fe
2O
3 + 6 HCl → 2 FeCl
3 + 3 H
2O
Both iron(III) chloride and PAC are used as
flocculation and coagulation agents in
wastewater treatment,
drinking water production, and
paper production.
Other inorganic compounds produced with hydrochloric acid include road application salt
calcium chloride,
nickel(II) chloride for
electroplating, and
zinc chloride for the
galvanizing industry and
battery production.
Production of organic compounds
The largest hydrochloric acid consumption is in the production of
organic compounds such as
vinyl chloride for
PVC. This is often captive use, consuming locally-produced hydrochloric acid that never actually reaches the open market. Other
organic compounds produced with hydrochloric acid include
bisphenol A for
polycarbonate,
activated carbon, and
ascorbic acid, as well as numerous
pharmaceutical products.
Other applications
Hydrochloric acid is a fundamental chemical, and as such it's used for a large number of small-scale applications, such as
leather processing, household
cleaning, and
building construction. In addition, a way of stimulating
oil production is by injecting hydrochloric acid into the rock formation of an
oil well, dissolving a portion of the rock, and creating a large-pore structure. Oil-well acidizing is a common process in the
North Sea oil production industry.
Many chemical reactions involving hydrochloric acid are applied in the production of
food, food
ingredients, and
food additives. Typical products include
aspartame,
fructose,
citric acid,
lysine, hydrolyzed (vegetable)
protein as food enhancer, and in
gelatin production. Food-grade (extra-pure) hydrochloric acid can be applied when needed for the final product.
Presence in living organisms
Physiology and pathology
Hydrochloric acid constitutes the majority of
gastric acid, the human
digestive fluid. In a complex process and at a large energy burden, it's secreted by
parietal cells (also known as oxyntic cells). These cells contain an extensive secretory network (called canaliculi) from which the HCl is secreted into the
lumen of the stomach. They are part of the
fundic glands (also known as oxyntic glands) in the
stomach.
Safety mechanisms that prevent the damage of the
epithelium of digestive tract by hydrochloric acid are the following:
- Negative regulators of its release
- A thick mucus layer covering the epithelium
- Sodium bicarbonate secreted by gastric epithelial cells and pancreas
- The structure of epithelium (tight junctions)
- Adequate blood supply
- Prostaglandins (many different effects: they stimulate mucus and bicarbonate secretion, maintain epithelial barrier integrity, enable adequate blood supply, stimulate the healing of the damaged mucous membrane)
When, due to different reasons, these mechanisms fail,
heartburn or
peptic ulcers can develop. Drugs called
proton pump inhibitors prevent the body from making excess acid in the stomach, while
antacids neutralize existing acid.
In some instances, the stomach doesn't produce enough hydrochloric acid. These pathologic states are denoted by the terms
hypochlorhydria and
achlorhydria. They have the potential to lead to
gastroenteritis.
Chemical weapons
Phosgene (COCl
2) was a common
chemical warfare agent used in
World War I. The main effect of
phosgene results from the dissolution of the gas in the mucous membranes deep in the
lung, where it's converted by
hydrolysis into
carbonic acid and the corrosive hydrochloric acid. The latter disrupts the
alveolar-
capillary membranes so that the lung becomes filled with fluid (
pulmonary edema).
Hydrochloric acid is also partly responsible for the harmful or blistering effects of
mustard gas. In the presence of
water, such as on the moist surface of the eyes or lungs, mustard gas breaks down forming hydrochloric acid.
Safety
Hydrochloric acid in high concentrations forms acidic mists. Both the mist and the solution have a corrosive effect on human tissue, with the potential to damage respiratory organs, eyes, skin, and intestines. Upon mixing hydrochloric acid with common oxidizing chemicals, such as
bleach (NaClO) or
permanganate (KMnO4), the toxic gas
chlorine is produced. To minimize the risks while working with hydrochloric acid, appropriate precautions should be taken, including wearing rubber or PVC gloves, protective eye goggles, and chemical-resistant clothing.
The hazards of solutions of hydrochloric acid depend on the concentration. The following table lists the
EU classification of hydrochloric acid solutions:
The
Environmental Protection Agency rates and regulates hydrochloric acid as a
toxin.
Further Information
Get more info on 'Hydrochloric Acid'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://hydrochloric_acid.totallyexplained.com">Hydrochloric acid Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
