Hydrochloric Acid Chemical Formula and Properties
Formula: HCl
Molar mass: 36.46 g/mol
Appearance: Colourless, transparent liquid
It is a simple diatomic molecule consisting of a hydrogen atom and a chlorine atom connected with a covalent single bond. Since the chlorine atom is much more electronegative than the hydrogen atom, the covalent bond between the atoms is polar.
What is Hydrochloric Acid?
Hydrochloric Acid is a strong corrosive Acid
A solution of hydrogen chloride in water is known as Hydrochloric Acid. Its Chemical formula is HCl
It has a unique pungent smell
One of its common application is that it is commonly used a laboratory reagent
It is used both in its aqueous and gaseous form
Occurrence
It is a major component of the gastric juice also referred to as the gastric Acid.
Preparation of Hydrochloric Acid
Hydrochloric Acid is prepared by dissolving hydrogen chloride and water. When hydrogen chloride gas enters the water, the water molecules take the hydrogen atom in HCl(g) and pull it away from the chlorine atom. This is the dissolution process, which makes Hydrochloric Acid.
\[HCl + H_{2}O \rightarrow H_{3}O + Cl^{-}\]
Hydrogen chloride is also generated as by-products from industrial-scale production of other Chemicals. Industrially it is prepared by the combustion of hydrogen in chlorine. Due to evaporation, the high concentration of HCl is hard to prepare.
Uses of Hydrochloric Acid
Hydrochloric Acid is a strong Acid as it is completely dissociated in water.
It can be used to prepare salts containing Cl- ions called chlorides.
It is also used in titration for determining the number of bases as it is a strong Acid and will give more precise results.
Hydrochloric Acid is also used to prepare samples in Chemical analysis.
Concentrated Hydrochloric Acid can dissolve a variety of metals to form hydrogen gas and oxidized metal chlorides.
What Makes HCl an Excellent Acidifying Agent?
It is a pure reagent and least hazardous to handle. It consists of non-corrosive and non- reactive chloride ions.
Physical Properties of Hydrochloric of Acid
The physical properties like boiling and melting points, density, and pH, of Hydrochloric Acid, varies depending on the concentration of Hydrochloric Acid in water. It is colorless with a highly pungent odor.
Chemical Properties of HCl
HCl is a strong Acid.
It is monoprotic therefore it can only release one proton (H+). In water; it completely dissociates to form hydrogen and chloride ions. The reason Hydrochloric Acid dissociates into hydrogen and chloride ions is because it is a polar covalent compound and therefore when added to water it ionizes.
Concentrated Hydrochloric Acid can dissolve metals and form oxidized metal chlorides and hydrogen gas
HCl is very corrosive; it attacks many metals like mercury, gold, platinum, tantalum, silver, and certain alloys are an exception.
Non-corrosive in presence of glass.
Applications
Hydrochloric Acid is a strong inorganic Acid that is used in a variety of industrial processes.
1) Pickling of Steel
\[ Fe_{2}O_{3} + Fe + 6 HCl \rightarrow 3 FeCl_{2} + 3 H_{2}O\]
This is a process in which dilute Hydrochloric Acid is used to remove rust or iron oxide from iron or steel before processing it for further wire production, a coating of sheet and strip, and tin mill products. This is required for all steel products that need further processing.
2) Cleaning Agent
Hydrochloric Acid can be used to clean any material that can withstand its effects as it is extremely powerful. It is also used to neutralize swimming pools if the pH level is high. This is done by pouring it into the pool while the pool pump is on.
3) To Regulate pH
Hydrochloric Acid is also used to regulate the Acidity pH of solutions. It is used to regulate the pH in a variety of manufacturing and treatment processes such as pharmaceuticals, swimming pools, drinking water, beverages, and food.
4) Production of Inorganic Compounds
Many inorganic compounds can be produced from simple Acid-based reactions resulting in inorganic compounds.
Some of them are listed below:
Water treatment Chemicals such as iron (III) chloride and polyaluminium chloride (PAC) are also included in the list.
\[ Fe_{2}O_{3} + 6 HCl → 2 FeCl_{3} + 3H_{2}O\]
Both PAC and iron (III) chloride are used as coagulation and flocculation agents in drinking water production, wastewater treatment, and paper production.
Zinc chloride for galvanizing industry and battery production
Calcium chloride and nickel (II) chloride for electroplating
\[ CaCO_{3} + 2 HCl \rightarrow CaCl + CO_{2} + H_{2} O \]
5) Production of Organic Compounds
Hydrochloric Acid is used in the production of organic compounds like vinyl chloride and dichloromethane which are used to produce PVC (polyvinyl chloride). Other than this Hydrochloric Acid is used to produce a variety of organic compounds like ascorbic Acid and pharmaceutical products.
6) Gastric Acid
Hydrochloric Acid is an important part of gastric juice produced in the body which helps in digestion. In the stomach, inactive pepsinogen is converted into active pepsin by HCl which then helps digestion by breaking the bonds linking amino Acids, a process known as proteolysis.
Hazards of Hydrochloric Acid?
If a small amount of Hydrochloric Acid is inhaled, it results in eye, nose, respiratory tract irritation and inflammation in humans, oral exposure can result in damage to the mucous membranes, stomach, esophagus etc. However continuous exposure to Hydrochloric Acid can result in gastritis, chronic bronchitis etc
Difference Between Hydrogen Chloride and Hydrochloric Acid?
Both hydrogen chloride and Hydrochloric Acid have the same formula. The difference is in the physical states they exist in. Hydrogen chloride is in a gaseous state while Hydrochloric Acid is in an aqueous solution.
So, this is all about Hydrochloric Acid. Applications of Hydrochloric Acid are one of the most important aspects of this section.
There are different methods of categorizing the Acids and Bases. Arrhenius Acid-Base and Lewis Acid base are the common methods used.
Arrhenius Acid-Base
Arrhenius Acid is such a substance that when mixed with water will dissociate and yield electrically charged atoms which increase the concentration of Hydrogen (H+) ions in the water. The H+ can’t exist alone in water as such but exist in the form of hydronium (H3O+) ions. Since it results in the increase in concentration of H+ ion, Arrhenius Acids are also known as proton donors or hydrogen ion donors.
On the other hand, Arrhenius bases are those substances which when dissociated with water yield increase in the concentration of Hydroxide (OH-) ions. Further these are strong Acid, strong base or weak Acid and weak base. This classification is dependent on the number of respective H+ and OH- ions produced upon dissociation in water.
Is Hydrochloric Acid(HCl) an Arrhenius Acid?
Hydrochloric Acid(HCl) is an arrhenius Acid, this can be confirmed from the Chemical equation given below which shows the reaction of Hydrochloric Acid(HCl) with water.
\[ HCL +H_{2}O \rightarrow H_{3}O^{+} +CL^{-}\]
Upon reaction with water, there is a yield of H3O+ AND Cl- ion. This means we get a hydronium ion in this reaction. The hydronium ion is further dissociated and the release of H+ ion can be seen as in the reaction shown below.
\[ H_{3}O^{+} \rightarrow H_{2}O + H^{+}\]
Thus upon dissociation the Hydronium ion will result in release of a water molecule (H2O) and a hydrogen (H+) ion which will increase the concentration of H+ ions in the water. Hence,Hydrochloric Acid(HCl) is an Arrhenius Acid as it follows the definition of an Arrhenius Acid.
Hydrochloric Acid(HCl) as Lewis Acid
This is another way of defining Acids and bases, here the donation of an electron pair is the defining matter. The substance that is capable of accepting an electron pair is known as Lewis Acid and the substance capable of donating an electron pair is defined as an Lewis Base.
Is Hydrochloric Acid(HCl) as Lewis Acid?
Hydrochloric Acid(HCl) is capable of accepting an electron pair. The H+ ion in the H-Cl has a valence orbital where an electron pair can reside. The electron pair can be accepted from any lewis base that is capable of donating an electron pair. For example water.
In the reaction between water (H2O) and Hydrochloric Acid(HCL), the Oxygen (O) in water has a free electron pair which can be donated, and Hydrogen (H) in Hydrochloric Acid is capable of accepting that electron pair. When they react, the oxygen atom of water donates its free electron pair to the hydrogen atom of Hydrochloric Acid. Thus Hydrochloric Acid acts as a lewis Acid.
What is the Strength of Hydrochloric Acid(HCl)?
The estimate of the strength of an Acid is defined by the ease with which the Acid is able to release its proton i.e the hydrogen ion (H+) to the base it is reacting with or the ease with which the Acid releases its proton i.e the hydrogen ion (H+) upon disassociation . The relative strength of Hydrochloric Acid (HCl) with respect to other common Acids used is shown as below
Perchloric Acid (HClO4)> Hydrochloric Acid (HCl) > Sulfuric Acid (H2SO4) >Nitric Acid (HNO3)
In this comparison we can evaluate that Hydrochloric Acid (HCl) is a slightly weaker Acid than Perchloric Acid but is a very strong Acid as compared to Sulfuric Acid and Nitric Acid.
What is the Structure of Hydrochloric Acid(HCl) ?
Hydrochloric Acid (HCl) is a diatomic molecule as explained above. The two molecules are present in a straight line at an angle of 90o to each other. There is no complex structure involved here. However the components formed from reaction with Hydrochloric Acid (HCl) can have complex structures, for example on reaction with water the hydronium ion formed has a little complex structure with the atoms inclined at different angles with respect to the central oxygen atom.
Hydrochloric Acid is very commonly used commercially and in Chemical experiments in schools and colleges. The Acid is comparatively easy to handle and doesn’t pose a severe threat when used in diluted form and for a little time of exposure to this Acid. Hydrochloric Acid (HCl) is also found in the stomach of humans and acts as a major factor in helping digestion in humans. The Acid doesn’t however damage the stomach because of the mucus layer present inside of the human stomach. However upon drinking of beverages or eating of food which results in Acid formation in the stomach, the Acidic balance of the stomach can change and the Hydrochloric Acid (HCl) can become more stronger and concentrated and hence cause Acidity problems or even ulcers. It is therefore advised that water intake for a human should be nominal so that the Hydrochloric Acid (HCl) present in the human stomach doesn’t get too concentrated and cause problems.
