Complete guide to hydrochloric acid: uses, safety & health risks

What Is hydrochloric acid?

Hydrochloric acid, also known as muriatic acid, is an inorganic chemical compound with the formula HCl. This colorless compound with a characteristic pungent odor is classified as a strong acid and commonly used as a laboratory reagent; also finds use in a wide range of industrial applications. The aqueous form is called the hydrochloric acid, while the gaseous form is called hydrogen chloride. Both, hydrochloric acid and hydrogen chloride have the same chemical formula; what makes them different is their state of matter, one is gaseous while the other is in liquid form.

Hydrochloric acid forms a major component of gastric acid, which is naturally produced in the human stomach to help digestion. It also finds a wide range of industrial and commercial applications with the demand growing each year.

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Properties of hydrochloric acid

The physical and chemical properties of hydrochloric acid is described in detail.

Physical properties

AppearanceClear, colorless liquid
OdorCharacteristic pungent odor
pHDepends on the concentration
Melting PointDepends on the concentration
Boiling PointDepends on the concentration
DensityDepends on the concentration

Chemical properties

  • HCl is one of the strongest acids
  • It is a highly corrosive acid
  • It is non-corrosive in presence of glass, hence, stored in glass container
  • Concentrated hydrochloric acid can dissolve metals
  • It can form oxidized metal chlorides
  • Gaseous hydrogen chloride, in presence of humidity, readily responds to the chlorides formed by active metals and their oxides, hydroxides, and carbonates
  • It involves metal reactions in which hydrogen gas is displaced

How is hydrochloric acid produced?

HCl can be produced in several different processes; some of the significant ones are discussed.

Using rock salt

2NaCl + H2SO4         -> 2HCl + Na2SO4

Historically, hydrochloric acid was produced by reaction between rock salt and sulphuric acid.

Rock salt    Sulphuric                Hydrochloric

                    acid                         acid       

By-product of chlorination reaction

The most common process to manufacture HCl is obtaining it as a by-product of the chlorination reaction. During the chlorination reaction, the gas stream containing hydrogen chloride is sent to the absorption column; here the absorption of hydrogen chloride vapors into a weak solution of hydrochloric acid continues which further produces concentrated hydrochloric acid.

Electrolysis of brine solution

Hydrochloric acid is also produced in the chlor-alkali industry. It is a two-step reaction which involves the electrolysis of brine solution to produce chlorine in the first step; and, the final step involving the reaction of pure chlorine gas with hydrogen to produce hydrogen chloride in the presence of the UV light. The hydrogen chloride produced in the reaction is absorbed in deionized water to produce pure hydrochloric acid.

2NaCl + 2H2O -> Cl2 + 2NaOH + H2

Sodium       Water         chlorine   Sodium   Hydrogen

Chloride                                          Hydroxide

Cl2 (g) + H2 (g) -> 2HCl (g)

Chlorine      Hydrogen        Hydrochloric acid

Uses of hydrochloric acid

Hydrochloric acid is the most ‘essential’ chemical used in a wide range of applications. The important applications include:

  • Used as laboratory reagent to regulate pH of solutions
  • Used in chloride productions
  • Used in gelatin production
  • Used to neutralize swimming pool when pH levels are high
  • Used in manufacturing of dyes
  • It is used in the production of fireworks
  • HCl forms the important constituent of gastric juice in the body, which helps in digestion
  • It is used in the production of batteries and photoflash bulbs
  • It is used in removing metal stains
  • Used in the purification process of table salt
  • It is an important ingredient in household cleaners
  • Used in oil production process
  • Used in food production and processing
  • It is used in calcium chloride production, which is further used to de-ice roads
  • It is used in leather processing

Industrial applications

Hydrochloric acid is used in a wide range of industrial applications that includes:

Cleaning agent

Hydrochloride acid is widely used as cleaning agent in industrial processes.

Regulate pH of solution

In manufacturing processes of pharmaceuticals, food, and beverages, hydrochloric acid is used to regulate the pH of the solution.

Pickling of steel

In the production of steel products, dilute hydrochloride acid is used to remove rust or iron oxide from iron and steel before further processing.

Production of organic compounds

HCl is used in the production of important organic compounds like dichloroethane and vinyl chloride, which are further used in the manufacture of polyvinyl chloride (PVC). It is also used in the production of various medicinal products.

Production of inorganic compounds

Hydrochloric acid is used in the production of various inorganic compound. It is used in the production of important water treatment chemical such as iron (III) chloride and polyaluminium chloride (PAC). These chemicals are used as coagulation and flocculation agents to clarify and purify drinking water and sewage treatment.

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Top manufacturers of hydrochloric acid

The wide range of application of hydrochloric acid within the industry has increased the demand for the chemical, thereby, increasing the production. The HCl market is estimated to reach a value of $1.9 billion in the year 2025, growing at a CAGR of 4.5%. The major factors driving the market are the increasing use of HCl in the industrial applications, production of organic and inorganic compounds, demand for pickling in the steel industry, and the ever-increasing demand from the oil and gas industry.

It is estimated that the Asia-Pacific region dominates the global hydrochloric acid market, with the increasing demand for the chemical in China and India.

Key players in the hydrochloric acid market

  • Solvay
  • Dow Chemicals
  • AGC Chemicals
  • Occidental Petroleum Corporation
  • Allan Chemical Corporation
  • AkzoNobel N.V.,
  • GFC Chemicals
  • Eco-Tec
  • Basic Chemical Solutions, LLC

Safety & health hazards of hydrochloric acid

Hydrochloric acid is a highly corrosive chemical that can severely affect the eyes, skin, and the mucous membrane. The damage is often irreversible or even fatal in extreme cases. The severity of the effect depends on the concentration of HCl being exposed.

Health Hazard in humans

Acute effects

  • Acute inhalation exposure of HCl may cause cough, hoarseness, and inflammation. In some cases, ulceration of the respiratory tract is found along with chest pain and pulmonary edema.
  • Acute hydrochloric acid exposure to eyes can induce chemical burns, and irreversible corneal damage in most of the cases.
  • Ingestion may cause corrosion of the mucous membranes, esophagus, and stomach. Common symptoms may include nausea, vomiting, and diarrhea. 
  • The acute skin exposure may produce severe burns, ulceration, and scarring.

Chronic effects

  • Chronic occupational exposure to hydrochloric acid can cause gastritis, chronic bronchitis, dermatitis, and photosensitization.
  • Prolonged exposure to low concentrations of hydrochloric acid may also cause dental discoloration and erosion.
  • Chronic inhalation exposure caused hyperplasia of the nasal mucosa, larynx, and trachea and lesions.

It is to be noted that there is no information available on the carcinogenic, reproductive, or developmental effects of HCl found in the humans.

First-aid measures

Eye contact: Flush the eyes with plenty of cold water at least for 10-15 minutes and get medical help soon after. Ensure to remove the contact lens while rinsing.

Skin contact: Make sure to remove the contaminated clothes immediately. Wash the affected area with soap and water, and rinse it with cold water for at least 15 minutes. Get medical help.

Inhalation: Immediately move the affected person to fresh air; visit doctor if the symptoms of coughing or irritation still persist.

Ingestion: Rinse the mouth thoroughly and drink sips of water, and visit the doctor immediately. Do not induce vomiting.

Safety handling and storage

Precautions for handling

  • Since HCl is a highly-corrosive chemical, it is important to wear the necessary Personal Protective Equipment.
  • Always add acid to water, and NOT the other way around.
  • Prevent the formation of aerosols.
  • Strictly follow the good laboratory hygiene practices.
  • Always use the chemical in a well-ventilated space.
  • HCl can corrode metallic surfaces, hence, keep them away from oxidizing agents, organic materials, metals, and alkalis.

Conditions for safe storage

  • Always store in a cool place away from sunlight.
  • Keep away from edible stuff.
  • Always read the specifications and store in containers with compatible material.
  • Preferred storage materials include glass, polyethylene, polypropylene, carbon steel lined with rubber, or ebonite.
  • Store in tightly closed containers.

It is to be noted that disposing of hydrochloric acid should be done with utmost care as it is treated as a hazardous waste. Make sure to dilute the HCl before disposing it to reduce the corrosive effects of the chemical. Always keep a source of cold water to be prepared for situations of unexpected spills or splashes. Dissolve baking soda of approximately 4-5 cups in a 5-gallon bucket filled with 1/4 water. Keep pouring the acid slowly into the bucket until all the fizz settles down, and dispose the solution.