Hydrochloric acid, also known as muriatic acid, is an inorganic acid. Hydrochloric acid formula, also known as muriatic acid, is given and discussed here and its structure. It is a strong acid and is corrosive. Hydrochloric acid is a solution of hydrogen chloride gas in water. It is one of the components of the gastric acid in our digestive system. 

Let us learn in-depth about hydrochloric acid and its formula in this article. 

Hydrochloric Acid Formula

The chemical formula of hydrochloric acid is \({\text{HCl}}{\text{.}}\) Hydrochloric acid is the aqueous solution of hydrogen chloride. Therefore, we use the formula \({\text{HCl}}\) for both hydrochloric acid and hydrogen chloride. It is a diatomic molecule. The hydrogen and chlorine atom in \({\text{HCl}}\) is joined through a single covalent bond which is formed by the sharing of electrons between hydrogen and chlorine atoms. As chlorine is more electronegative than hydrogen, the bond between them is polar.

Structure of Hydrochloric Acid

Hydrochloric acid is a simple diatomic molecule containing hydrogen and chlorine atoms. The structure of hydrochloric acid can be given as,

Hydrochloric acid has a linear shape. The molar mass or the molecular weight of hydrochloric acid is \(36.5\,{\text{g}}/{\text{mol}}.\)

Preparation of Hydrochloric Acid

Hydrochloric acid can be prepared by dissolving hydrogen chloride in water. For preparing hydrogen chloride, we can use the following methods:

1. Hydrogen chloride can be prepared by using the salt cake method. This method involves the addition of concentrated sulphuric acid \(\left({{{\text{H}}_2}{\text{S}}{{\text{O}}_4}} \right)\) to rock salt \(\left({{\text{NaCl}}} \right).\) The reaction is done in two stages at different temperatures.

Stage 1: In this stage, the solid sodium chloride \(\left({{\text{NaCl}}}\right)\) is heated with concentrated sulphuric acid \(\left({{{\text{H}}_2}{\text{S}}{{\text{O}}_4}} \right)\) at \(420\,{\text{K}}.\) The chemical reaction can be given as,

Stage 2: In the second stage, the mixture is heated to around \(823\,{\text{K}}.\) The reaction thus produces \({\text{N}}{{\text{a}}_2}{\text{S}}{{\text{O}}_4}\) and \({\text{HCl}}.\) The reaction can be given as,

The \({\text{HCl}}\) gas can be dried out by passing it through concentrated sulphuric acid, and the byproduct \({\text{N}}{{\text{a}}_2}{\text{S}}{{\text{O}}_4}\) obtained can be sold for paper making.
1. Pure hydrogen chloride can be manufactured by the direct combination of hydrogen \(\left({{{\text{H}}_2}} \right)\) and chlorine gas \(\left({{\text{C}}{{\text{l}}_2}} \right).\)
2. It is also obtained as a by-product from the large scale production of other chemicals.

Properties of Hydrochloric Acid

The physical and chemical properties of hydrochloric acid are explained below:

Physical Properties of Hydrochloric Acid

Hydrochloric acid is a colourless liquid with a pungent smell. As hydrochloric acid is the solution of hydrogen chloride in water, the concentration of hydrogen chloride in water differs in various solutions. Therefore, the other physical properties such as the density, melting and boiling points, etc. will depend on the concentration of hydrogen chloride in the aqueous solution.

Chemical Properties of Hydrochloric Acid

1. Acidic properties of Hydrochloric Acid

Hydrochloric acid is a strong acid. It behaves as an electrolyte. That is, the water being a polar solvent helps to ionize \({\text{HCl}}\) to give hydronium \(\left({{{\text{H}}_3}{{\text{O}}^ + }} \right)\) ions. Due to the presence of such ions, it shows acidic properties, and also makes it a good electrolyte as it conducts electricity.

\({\text{HCl}} + {{\text{H}}_2}{\text{O}} \to {{\text{H}}_3}{{\text{O}}^ + } + {\text{C}}{{\text{l}}^ – }\)

2. Chemical reactions of dilute Hydrochloric Acid

The reactions of dilute hydrochloric acid with different substances can be given as,

Reaction with Active Metals

Generally, dilute hydrochloric acid reacts with metals to liberate hydrogen gas. The examples of such reactions can be given as,

\({\text{Fe}} + 2{\text{HCl}} \to {\text{FeC}}{{\text{l}}_2} + {{\text{H}}_2} \uparrow \)
\({\text{Zn}} + 2{\text{HCl}} \to {\text{ZnC}}{{\text{l}}_2} + {{\text{H}}_2} \uparrow \)
\({\text{Ca}} + 2{\text{HCl}} \to {\text{CaC}}{{\text{l}}_2} + {{\text{H}}_2} \uparrow \)
\({\text{Mg}} + 2{\text{HCl}} \to {\text{MgC}}{{\text{l}}_2} + {{\text{H}}_2} \uparrow \)

Reaction with Bases

Hydrochloric acid reacts with bases (such as metallic oxides, hydroxides, etc.) to give salt and water as the products. Such reactions are generally called as neutralization reactions. The examples of such reactions can be given as,

\({\text{ZnO}} + 2{\text{HCl}} \to {\text{ZnC}}{{\text{l}}_2} + {{\text{H}}_2}{\text{O}}\)
\({\text{MgO}} + 2{\text{HCl}} \to {\text{MgC}}{{\text{l}}_2} + {{\text{H}}_2}{\text{O}}\)
\({\text{NaOH}} + {\text{HCl}} \to {\text{NaCl}} + {{\text{H}}_2}{\text{O}}\)
\({\text{Ca}}{\left({{\text{OH}}} \right)_2} + {\text{HCl}} \to {\text{CaC}}{{\text{l}}_2} + 2{{\text{H}}_2}{\text{O}}\)

Reaction with Metal Carbonates and Bicarbonates

When dilute hydrochloric acid reacts with metal carbonate or bicarbonates, carbon dioxide gas is liberated. The examples of such reactions can be given as,

\({\text{N}}{{\text{a}}_2}{\text{C}}{{\text{O}}_3} + 2{\text{HCl}} \to 2{\text{NaCl}} + {{\text{H}}_2}{\text{O}} + {\text{C}}{{\text{O}}_2} \uparrow \)

\({\text{NaHC}}{{\text{O}}_3} + {\text{HCl}} \to 2{\text{NaCl}} + {{\text{H}}_2}{\text{O}} +{\text{C}}{{\text{O}}_2} \uparrow \)

\({\text{Ca}}{\left({{\text{HC}}{{\text{O}}_3}} \right)_2} + 2{\text{HCl}} \to {\text{CaC}}{{\text{l}}_2} + 2{{\text{H}}_2}{\text{O}} + 2{\text{C}}{{\text{O}}_2} \uparrow \)

\({\text{Mg}}{\left({{\text{HC}}{{\text{O}}_3}} \right)_2} + 2{\text{HCl}} \to {\text{MgC}}{{\text{l}}_2} + {{\text{H}}_2}{\text{O}} + {\text{C}}{{\text{O}}_2} \uparrow \)

Reaction with Metal Sulphites and Bisulphites

Sulphur dioxide gas is liberated when dilute hydrochloric acid reacts with metal sulphites and bisulphites. The examples of such reactions can be given as,

\({\text{ZnS}}{{\text{O}}_3} + 2{\text{HCl}} \to {\text{ZnC}}{{\text{l}}_2} + {{\text{H}}_2}{\text{O}} + {\text{S}}{{\text{O}}_2} \uparrow \)

\({\text{N}}{{\text{a}}_2}{\text{S}}{{\text{O}}_3} + 2{\text{HCl}} \to 2{\text{NaCl}} + {{\text{H}}_2}{\text{O}} + {\text{S}}{{\text{O}}_2} \uparrow \)

\({\text{NaHS}}{{\text{O}}_3} + {\text{HCl}} \to {\text{NaCl}} + {{\text{H}}_2}{\text{O}} + {\text{S}}{{\text{O}}_2} \uparrow \)

\({\text{Ca}}{\left({{\text{HS}}{{\text{O}}_3}} \right)_2} + {\text{HCl}} \to {\text{CaC}}{{\text{l}}_2} + 2{{\text{H}}_2}{\text{O}} + 2{\text{S}}{{\text{O}}_2} \uparrow \)

Reaction with Metallic Sulphide

When dilute hydrochloric acid is reacted with a metallic sulphide, hydrogen sulphide gas which has a smell of rotten eggs is evolved. The examples of such reactions can be given as,

\({\text{FeS}} + 2{\text{HCl}} \to {\text{FeC}}{{\text{l}}_2} + {{\text{H}}_2}~{\text{S}} \uparrow \)

\({\text{ZnS}} + 2{\text{HCl}} \to {\text{ZnC}}{{\text{l}}_2} + {{\text{H}}_2}~{\text{S}} \uparrow \)

Reaction with Silver Nitrate

When dilute hydrochloric acid reacts with silver nitrate, a curdy white precipitate of silver chloride is obtained. It is insoluble in nitric acid but dissolves in excess of ammonium hydroxide due to the formation of a soluble complex, diammine silver chloride.

\({\text{AgN}}{{\text{O}}_3} + {\text{HCl}} \to {\text{AgCl}} \downarrow + {\text{HN}}{{\text{O}}_3}\)

Reaction with Lead Nitrate

When dilute hydrochloric acid is reacted with lead nitrate, a chalky white precipitate of lead chloride which is soluble in water is obtained. The equation for the reaction can be given as,

\({\text{Pb}}{\left({{\text{N}}{{\text{O}}_3}} \right)_2} + 2{\text{HCl}} \to {\text{PbC}}{{\text{l}}_2} \downarrow + 2{\text{HN}}{{\text{O}}_3}\)

Reaction of Hydrochloric acid with Ammonia

When a glass rod dipped in ammonia solution is brought near the vapours of hydrochloric acid, it gives dense white fumes of ammonium chloride. That is,

Learn Theories of Acids and Bases

Uses of Hydrochloric Acid

Hydrochloric acid has got many uses. They are:

1. Hydrochloric acid is used for the manufacture of plastics like PVC and polyurethane.
2. It is used in the production of chlorine, glucose and ammonium chloride.
3. It is used as a laboratory reagent.
4. It is used in medicines.
5. Hydrochloric acid is used for extracting glue from bones.
6. It is used in the production of dyes.
7. It is used in textile industry.
8. It is used for making cleaning products.

Aqua Regia: When three parts of concentrated hydrochloric acid are mixed with one part of nitric acid, a mixture called aqua regia is obtained. This aqua regia can be used for dissolving noble metals such as gold and platinum.

Study Acid Strength of Hydrogen Halides

Summary

Hydrochloric acid is a strong acid with great properties. In this article, we have learnt about hydrochloric acid in detail. The chemical formula, structure, preparation, physical and chemical properties of hydrochloric acid and its utilization in the industrial field.

FAQs

Q.1. What is the chemical formula of hydrochloric acid?
Ans: The chemical formula of hydrochloric acid is \({\text{HCl}}.\) It is strong inorganic acid which is also known as muriatic acid.

Q.2. How to write the hydrochloric acid formula?
Ans: Hydrochloric acid contains one atom of hydrogen and one atom of chlorine. In hydrochloric acid, the valency of hydrogen is one and that of chlorine is also one. By crisscrossing the valencies of both hydrogen and chlorine, its chemical formula can be written as \({\text{HCl}}.\)

Q.3. Is hydrochloric acid used for cleaning?
Ans: Yes, hydrochloric acid is used as an ingredient in common household cleaners such as bathroom floor cleaners, toilet bowl cleaners, porcelain cleaners. etc. This is because hydrochloric acid is corrosive in nature. Hence, it can help to clean tough stains on surfaces.

Q.4. Why does \({\text{HCl}}\) burn skin?
Ans: Hydrochloric acid is a strong acid. It is highly corrosive in nature too. Therefore, when concentrated hydrochloric acid comes in contact with skin, it can cause skin burns. It can destroy the skin cells too.

Q.5. What can hydrochloric acid be used for?
Ans: Hydrochloric acid has got many uses. It is used as a laboratory reagent, used for the manufacture of plastics, used in the production of chlorine, glucose and ammonium chloride, etc. It is also used for extracting glue from bones.

Q.6. Do vinegar and salt make hydrochloric acid?
Ans: Yes, vinegar and salt react together to form hydrochloric acid. That is, salt is chemically sodium chloride and vinegar contains acetic acid in it. When they react together, sodium acetate and hydrochloric acid are produced. That is, \({\text{C}}{{\text{H}}_3}{\text{COOH}} + {\text{NaCl}} \to {\text{C}}{{\text{H}}_3}{\text{COONa}} + {\text{HCl}}\)

Q.7. Can hydrochloric acid melt skin?
Ans: No, concentrated hydrochloric acid gives severe burn to the skin if it comes in contact with it. Concentrated sulphuric acid and hydrofluoric acid can melt skin as they are highly corrosive and dangerous acids.

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