Hydrochloric Acid - The Definitive Guide | Dictionary of Biology (2023)


Hydrochloric acid is a corrosive acid formed by dissolving hydrogen chloride (HCl) in water and is therefore an aqueous solution of hydrogen halide. Hydrochloric acid is used in various industries as a cleaning, pickling or pH-regulating solution and is also found in diluted form in gastric juice. Hydrogen chloride is sometimes referred to as hydrochloric acid, hydronium chloride, chloran, salt spirit, or acidum salis.

Use of hydrochloric acid

The uses of hydrochloric acid range from physiological to industrial applications. In industry, HCl's strong corrosive properties and the fact that it is the simplest chlorine-based acid make it a cheap and effective, albeit dangerous and destructive, compound.The aqueous solution must be pressurized or refrigeratedor it turns into a harmful gas when water components evaporate and make up less than 60% of the total solution. While a complete list of uses for hydrochloric acid would fill many pages, the most common uses are discussed in more detail below.

In the industry

The use of industrial hydrochloric acid spans a wide variety of sectors. It is an important component of manufactured goods such as polyvinyl carbonate (PVC), bisphenol A (BPA) andEthylendichlorid(EDZ). BPA is used in the manufacture of polycarbonate plastics and epoxy resins, but has been the source of a health hazard due to its carcinogenic effects. For this reason, many plastics are now manufactured and advertised as BPA-free products. All of these organic compounds are used in the plastics industry and as laboratory solvents, but they can be highly carcinogenic.

Preparing metal for further processing involves one of two similar processes, pickling and passivating. While passivation provides a lighter effect, using mildly caustic acids to remove impurities left behind during metal fabrication, protecting the metal from contaminants, smoothing the surface and increasing durability, pickling achieves a more powerful effect through the use of a strong acid. This acid is usually hydrogen chloride. Metals treated in hydrochloric acid baths are referred to as HCl pickled metals.

Hydrochloric acid is often used in a single leather processing step in leather tanneries. The tanning of hides involves the introduction of a chromium salt to alter the collagen network within it, thus preventing future stains. Chromium salts are added to a bath with a pH between 2.5 and 3 together with sodium chloride. This is the pickling phase. The chromium is then fixed to the skin, raising the pH and known as the basification stage. Hydrogen chloride is necessary to achieve the low pH of the pickling stage.

Another industrial use of hydrogen chloride is in the manufacture of inorganic compounds such as polyaluminum chloride (PAC), ferric chloride (ferric trichloride) and aluminum chlorohydrate. The use of hydrogen chloride is necessary at the beginning of the production processes of these compounds, for example the addition of 20% HCl and sulfuric acid to bauxite for PAC manufacture. Aluminum salts are used in the cosmetics industry (e.g. in antiperspirant deodorants) or in the chemical coagulation and flocculation phase of drinking water and wastewater treatment, where added aluminum (or iron) cations neutralize the charge of pollutant colloid particles and allow them to separate to connect flakes (flocculation) can be sucked off.

HCl is also used to "clean" the salt used in food production and on our tables. In a saturated NaCl solution, there is a constant equilibrium between separate positive sodium and negative chloride ions and unionized NaCl. By passing HCl gas through this solution, it dissociates to form H+ and Cl- ions. Since the chloride ion is common to both sodium chloride and hydrogen chloride, its concentration increases and produces a shift according to Le Chatelier's principle. It means thatavailable sodium ions tend to bind to the freely available chloride, resulting in increased NaCl deposits. This process is called salt cleaning. Alternatively, you can convert hydrochloric acid to sodium hydroxide (NaOH) or sodium carbonate (Na2Co3) and both reactions form sodium chloride salt.

Of course, a strong acid like hydrogen chloride is also used to regulate the acidity of a variety of solutions used in pharmaceutical products, in food additives like fructose, citric acid, and hydrolyzed vegetable protein, in alkaline waste, and in our drinking water.

Hydrochloric acid is also used to increase oil production in oil wells. When injected into bedrock, it creates larger pores that can transport more oil downhole. These are just some of the more common uses of hydrochloric acid in industry.

(Video) The Importance of Hydrochloric acid (HCL) in the Stomach – Dr. Berg

in the house

Household use of hydrochloric acid is limited to lower concentrations that are less corrosive but still have admirable cleaning and pH-regulating properties. Those with swimming pools may want to try a 10 part water to 1 part HCl solution to remove grout stains.

The same solution removes stains from metals, so it's used in products sold to clean iron, copper, brass, and other metals. The effect is similar to pickling steel, oxidizing surface layers to remove stains and impurities. Most acids, including hydrogen chloride, will also remove limescale, but care must be taken with the concentration used. Most of the powerful cleaning products we use in the home contain HCl. If you spill muriatic acid on a sensitive surface, add a paste of baking soda and water to neutralize it; Keep it ready and handy to avoid maximum damage.

Acid-base reactions are often used to create an effervescent reaction meant to increase the power of an acidic detergent; However, you only speed up a reaction by adding an alkali, while the added acid should ideally serve to neutralize the alkalis on the dirty surface. Hydrochloric acid reacts with most carbonates and metals, for example with calcium carbonate to form calcium chloride, carbon dioxide and water, or with magnesium to form magnesium chloride, carbon dioxide and water.

In the human body

The stomach is the site of the early stages of digestion but plays a similarly important role where potential pathogenic microorganisms that may have been ingested are eliminated due to a highly acidic environment with a pH between 1.5 and 3.5.This acidity is the result of the production of hydrogen chloride in the stomach.

In the human body, HCl is produced by the parietal cells of the gastric mucosa. The parietal cell cytoplasm combines with water and carbon dioxide to produce carbonic acid. The enzyme carbonic anhydrase converts a carbonic acid ion into a single hydrogen ion (H+) and a single bicarbonate ion (HCO3). The hydrogen ion is transported to the stomach via the H+– K+ATPase channel that exchanges positive extracellular potassium ions with positive intracellular hydrogen ions. At the same time, the bicarbonate ions are transported from the cell into the blood via an anion exchanger, which exchanges bicarbonate ions for negative chloride ions. Parietal cells also have chloride channels in their membranes. Negative chloride ions are transported to the stomach as intracellular concentrations increase.

This process leads to the presence of hydrogen and chloride ions in the stomach. As negative and opposite ions, they attract and form hydrochloric acid. Hydrochloric acid is an important component of gastric juice, necessary to eliminate a wide range of potentially pathogenic bacteria before the stomach contents find their way into the highly absorbent environment of the gut.

The human body can regulate hydrochloric acid production through involuntary neuronal stimulation, initially during vagus nerve stimulation when food is seen or chewed. When food reaches the stomach and the stomach expands, the resulting nerve firings also stimulate the vagus nerve to produce more acetylcholine, which increases secretions such as saliva and gastric juice and gives more power to intestinal peristalsis. The third and most important method is the secretion of gastrin from the gastric mucosal G-cells, which are similarly activated by the vagus nerve, but also by peptides produced by the stomach, such as B. Gastrin-related peptides. Gastrin is a hormone that travels through the blood to the parietal cells, where they bind to cholecystokinin (CKK) hormones via CKKBreceptors and is part of the gut-brain connection that controls satiety and appetite.

With the increased production of gastrin and acetylcholine, another response takes place in the form of histamine release from enterochromaffin cells (ECL cells), which are located near the parietal cells in the gastric mucosa. This histamine binds to receptors on the parietal cells and stimulates them to produce more stomach acid.

The opposite effect - a decrease in hydrochloric acid production - occurs during periods of starvation, when there is no food in the stomach and acidity increases.High acidity stops the excretion of hydrogen and chloride ions in the parietal cell. It also stimulates D cells to produce somatostatin, which decreases production of the hormone gastrin. Food entering the duodenum also triggers a reflex known as the enterogastric reflex, a nerve pathway of the enteric nervous system that decreases vagus nerve stimulation. Food in the gut also decreases the availability (and thus the effect) of cholecystokinin, as well as secretin, which reduces the production of acidic components of gastric juice and increases the production of alkaline components. It can therefore be said with certainty that the secretion of hydrochloric acid in the digestive system is regulated by hormonal and neural pathways, which include gastrin, histamine, somatostatin, a number of polypeptides and the vagus nerve.

In war

The use of hydrochloric acid in warfare is most commonly associated with the production and effects of hydrochloric acidSenfgasor sulfur mustard, used in trench warfare during World War I,Nevertheless, it was recently used in the civil war in Syria, although the Chemical Weapons Convention banned its use in 1993. Normally not fatal unless exposed to high levels on a regular basis, this blistering agent attacks the skin and lining of the respiratory and gastrointestinal tract, causing burns, swelling, irritation and pus-filled blisters. Mustard gas also causes mutations in DNA and is a known carcinogen. There is no antidote.

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Various processes are used to make mustard gas, but only one of them - the Meyer-Clarke process - uses concentrated hydrochloric acid.

Another gas used in warfare is phosgene, with the formula COCl2. Unlike mustard gas, which has a slightly greenish-yellow hue, phosgene is colorless and smells like freshly cut hay. It is the result of carbon monoxide, activated charcoal and chlorine gas.Hydrochloric acid is not used in phosgene production, but is formed in the presence of water. Water is found in large quantities in the mucous membranes. This means that when inhaled or swallowed, phosgene is converted into carbonic and hydrochloric acid. While mustard gas resulted in a number of deaths, at least 80,000 deaths in World War I are believed to have been due to the harsher and more immediate effects of phosgene. This is approximately 85% of all chemical warfare-related deaths during this period.

hydrochloric acid facts

Hydrogen chloride is a compound made up of a one-to-one ratio of hydrogen and chlorine. Without the presence of water molecules, hydrogen chloride is a colorless but toxic gas. When adding water, hydrogen releases many of its hydrogen molecules to create a highly acidic solution. Just over 97% of the molecular weight of HCl is due to the single chloride ion. This chloride ion has an atomic mass of 35.543 and the hydrogen ion has an atomic mass of 1.00794. Since there is only one atom at a time, the molar mass of HCl is calculated by adding these two numbers - 36.46094 g/mol. As mentioned earlier, the formula of hydrogen chloride is HCl.

In the case of molecular weight, the results depend on the number of moles of HCl. For example, in a solution where many chloride-solute gas atoms are available (Cl2) for the number of molecular hydrogen atoms (H2), we can say with certainty that 4 moles of HCl gives 4.00 moles of HCl.

Using the equation Mass HCl = Moles HCl x Molar Mass HCl, we can determine that 4.00 moles x 36.46 g moles-1is 146g.

Hydrochloric acid density, pH, melting point and boiling point depend on the concentration. For example, a 10% HCl solution has a density of 1048 kg/l, a pH of -0.5, a melting point of -18°C and a boiling point of 103°C. A 30% HCl solution has a density of 1.149 kg/l, a pH of -1 and a melting and boiling point of -52 °C and 90 °C, respectively.

Handling Hydrochloric Acid - MSDS Note

Hydrochloric acid is a dangerous liquid, and it has its ownMaterial Safety Data Sheet(safety data sheet). This is information that lists the occupational safety and health factors associated with its use and must be available and easy to find in locations where potentially hazardous materials are found.

Hydrochloric acid is corrosive; concentrated forms also emit toxic acid mists. If either acid or mist comes into contact with the skin, eyes or internal organs, the damage can be irreversible or potentially fatal.Although HCl is not classified as a carcinogen, its industrial use requires personal protective equipmentB. a respirator, rubber gloves and boots and a face shield. In addition, all premises where hydrochloric acid is used should have access to an eyewash system. Even when cleaning at home with diluted products, splashes on eyes or skin can cause burns.

The MSDS recommendation for skin contact with hydrochloric acid is to flush the area for at least 15 minutes and remove all clothing that has come into contact with the solution. In case of visible burns, washing with antibacterial soap or using antibacterial cream and visiting a medical center are recommended. Contact with eyes requires an irrigating system that irrigates the affected eye for at least 15 minutes and requires medical attention.

Ingestion of hydrochloric acid of any concentration can cause burns in the mouth, throat, and esophagus. Although gastric juice is highly acidic, it remains in the stomach's reservoir. Indigestion caused by stomach acid rising up the lower esophagus can cause Barrett's esophagitis and increase the risk of esophageal cancer.A common disease of the gastrointestinal tract is gastroesophageal reflux disease or GERD. The image below shows the signs and symptoms of this often painful pathology. If HCl is swallowed, it is important not to vomit but seek immediate medical attention. Inhaling HCl mist also requires a visit to the emergency room.

(Video) regulation of acid production through parasympathetic nervous system | regulation of acid production

The safety data sheets for storage insist that hydrochloric acid must be stored in a closed and suitable container in a cool, dry and well-ventilated place. It should also be kept away from organic materials, oxidizers, metals and alkalis as it can react with these and increase levels of combustible hydrogen gas.


1. Which of the following organic compounds will be phased out in the plastics industry?
C.sulfuric acid

Answer to question #1

Bit's right. BPA, or Bisphenol A, is a carcinogen used in the manufacture of plastics and resins. Many plastics are now BPA-free and this trend is sure to continue.

2. What should you do first if you take hydrogen chloride?
A.drink lots of water
B.To throw up
C.Drink a bicarbonate solution
D.Seek medical treatment

Answer to question #2

Dit's right. Drinking water provides extra hydrogen molecules and can increase acidity, but more importantly, the acid will only wash further up the esophagus, increasing the damaged surface area. Vomiting increases acidity due to the presence of stomach acid. Bicarbonate or alkaline products cause a volatile reaction that may perforate the digestive tract. Medical attention is essential for procedures ranging from gastric lavage to intubation and transfer to an intensive care unit.

3. Where does coagulation and flocculation occur in relation to HCl?
A.pickling of metals
B.water supply
C.treatment of burns
D.salt cleaning


Answer to question #3

Bit's right. The coagulation and flocculation of contaminants in water allows for their easier removal, providing less contaminated water.

4. Which cells produce gastrin?
A.parietal cells
B.T cells
C.G cells
D.ECL cells

Answer to question #4

Cit's right. ECL cells produce histamine, T cells are involved in immunity, parietal cells secrete hydrogen and chloride ions and intrinsic factor. The letter G points us in the right direction - G cells produce gastrin.

5. Which cranial nerve is most involved in regulating gastric juice production?
A.Vagus nerve
B.kidnap nerves
C.Nervus hypoglossus
D.oculomotor nerve

Answer to question #5

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Ait's right. Both the abducens and oculomotor nerves play a role in eye movement. The hypoglossal nerve controls the tongue. The vagus nerve is essential to several nerve pathways that end in a variety of internal organs such as the heart, digestive system, and lungs.


What does hydrochloric acid do in biology? ›

Hydrochloric acid contributes to protein digestion by supplying H+ which activates pepsinogen, the precursor to pepsin. Pepsinogen is secreted by chief cells in the gastric glands of the body and antrum of the stomach.

What is the hydrochloric acid used for quizlet? ›

What is the role of HCL? Hydrochloric acid (HCl) converts pepsinogen to pepsin which breaks down proteins to peptides. HCl maintains a pH in the stomach. It also dissolves food and kills microorganisms.

What does hydrochloric acid do to the human body? ›

Hydrochloric acid in contact with skin or other tissues can cause chemical burns that can be severe. Hydrochloric acid in the eyes can cause blindness. The severity of the burns depends upon the concentration of the acid and the amount of time it is left in contact with the tissues.

Where is hydrochloric acid on the pH scale? ›

Hydrochloric acid (HCL) has a pH level of 1.1 at 38% concentration. If this acid accidently came into contact with your eyes or skin, it would immediately begin to dissolve your skin tissue.

What are the two main uses of hydrochloric acid? ›

It is often used in a diluted form. Hydrochloric acid is commonly used for cleaning tiles in kitchens and bathrooms and it also disinfects thoroughly. It is also used in the textile industry for bleaching clothes and processing leather in the leather tanning industry.

What organ produces hydrochloric acid? ›

A large, muscular chamber, the stomach produces digestive juices like pepsin, lipase, and hydrochloric acid, which digest and dissolve stomach contents.

What drug uses hydrochloric acid? ›

Methamphetamine is commonly prepared illicitly by the reduction of ephedrine or pseudoephedrine using red phosphorus and hydroiodic acid (figure 6). It is then converted to methamphetamine hydrochloride by adding hydrochloric acid.

Why is hydrochloric acid called an acid? ›

When HCl molecules dissolve they dissociate into H+ ions and Cl- ions. HCl is a strong acid because it dissociates almost completely. By contrast, a weak acid like acetic acid (CH3COOH) does not dissociate well in water – many H+ ions remain bound-up within the molecule.

What is acid found in the stomach called? ›

It helps digest food. Gastric acid is made of hydrochloric acid.

What foods have hydrochloric acid? ›

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.

What foods contain hydrochloric acid? ›

Stomach, or gastric, acid is a digestive fluid containing hydrochloric acid (HCL) and digestive enzymes.
Foods that naturally contain probiotics include:
  • yogurt.
  • cottage cheese.
  • kefir.
  • sauerkraut.
  • kimchi.
  • tempeh.
  • kombucha.
  • miso.
Jul 29, 2020

Where is hydrochloric acid located in the body? ›

Hydrochloric acid is the main component of gastric juice and is secreted by the parietal cells of the gastric mucosa in the fundus and corpus.

What is hydrochloric acid HCl quizlet? ›

Hydrochloric Acid. A strong acid and is the major component of gastric acid. Jabir ibn Hayyan. Discovered hydrochloric acid by mixing common salt with vitriol (sulfuric acid)

Is hydrochloric acid used to treat water? ›

Hydrochloric acid, also known as Muriatic Acid, is used widely in water treatment as an effective neutralization agent for alkaline (high pH) effluent. It is regarded as a very suitable alternative to sulfuric acid in this application as a result of the inorganic by-products that are generated in this process.


1. Acids, Bases, and pH
(Bozeman Science)
2. How To Name Acids - The Fast & Easy Way!
(The Organic Chemistry Tutor)
3. Stomach Acid HCL: Q and A
(Confluence Nutrition)
4. Uses of Hydrochloric Acid | Uses of acid | Acid | English |
(Zak1 Masud)
5. The Home Scientist 007 - Purify hydrochloric acid
6. Biology Lecture - 4 - Acids and Bases


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