Strong and Weak Acids

Last Updated : 10 Jan, 2024

Strong Acid is an acid that completely dissociates in an aqueous solution, while Weak Acid is an acid that partially dissociates in aqueous solution. Examples of strong acids are Hydrochloric acid (HCl), Sulfuric acid (H₂SO₄), Nitric acid (HNO₃), Chloric acid (HClO3), Hydrobromic acid (HBr), Hydroiodic acid (HI), and examples of weak acids are Hydrofluoric acid (HF), Nitrous acid (HNO₂), Sulfurous acid (H₂SO₃), Phosphoric acid (H₃PO₄), etc.

In this article, we are going to discuss what strong acid is, the list of strong acids, what weak acid is, and the list of weak acids.

Table of Content

What is Strong Acid?
List of Strong Acids
What is Weak Acid?
List of Weak Acids
Strong Acids vs Weak Acids
Table of Strong and Weak Acids

What is Acid?

Acid is a substance that generates hydrogen ions when dissolved in an aqueous solution. Another definition of Acid is acid, which is any hydrogen-containing compound that is capable of donating hydrogen ions to another substance.

There are different categories for the classification of Acids.
Acid is derived from the Latin word here, which means sour.
Acids are those substances that have a pH of less than 7.
Acids are sour in taste. Acids turn blue litmus paper into red and do not show any effect on red litmus paper.

Some examples of Acids are Hydrochloric acid, Sulfuric acid, Nitric acid, Acetic acid, Citric acid, Benzoic acid, and Hydrofluoric acid.

Types of Acids

Based on the dissociation in water Acids are classified as follows

Strong Acid
Weak Acid

Let’s discuss them one by one

What is Strong Acid?

Strong acids are those acid that dissociates completely in aqueous solution. They dissociate completely in cation and anion when dissolved in aqueous solution. They loose H⁺ ion very quickly in an aqueous solution. Strong acid has a lower pH because of its ability to lose all protons. Strong acids are good conductors of electricity in aqueous solution.

Strong Acid Definition

Strong Acid is defined as the acid which completely dissociates into H⁺ and OH^– ions in water

Dissociation of Strong Acids

Strong acids dissociated completely in aqueous solution. When they dissolved in aqueous solution they dissociate into cations and anions. In fact, we can say that any acid that is dissociated 100% completely is an example of strong acid. It releases H⁺ ion when dissolved in water as cation if the acid contain hydrogen atom as cation. Strong acids include HClO₄, H₂SO₄, HI, HBr, HCl, and HNO₃.

List of Strong Acids

List of Some strong acids are as follows:

Hydrochloric Acid (HCl)

Hydrochloric acid is an example of Strong acid.
The chemical formula of Hydrochloric acid is HCl.
Hydrochloric acid is aqueous solution of Hydrogen chloride.
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.
It is a strong corrosive colorless acid with pungent smell.

Sulfuric Acid (H₂SO₄)

Sulfuric acid is colorless and odorless strong acid that is corrosive in nature.
This acid has wide variety of applications in real life.
That’s why this acid is known as King of Chemicals.
The boiling point of the acid is 611 K.
The higher boiling point and thickness of this chemical is due to hydrogen bonding.
Sulfuric acid is very good oxidizing agent.
Concentrated sulfuric acid is a very strong dehydrating agent. Thus, this chemical is used for drying wet gases which do not react with the acid.

Nitric Acid (HNO₃)

It is a colorless strong acid that emits yellow or red fumes.
The chemical formula of Nitric acid is HNO_{3 .}
The shape of Nitric acid molecule is planar, with the nitrogen atom attached to three oxygen atoms, one of which holds the proton.
Other two N-O bonds are equivalent and show the resonance with double bond character.
Its boiling point is 83 deg C.
It slowly turns into yellow color as it gets older.
It is a common reagent used in laboratories and an important chemical used in many industries to manufacture explosives and fertilizers.

Hydrobromic Acid (HBr)

It is a colorless strong acid, which has chemical formula as HBr.
HBr is very reactive in nature and corrosive to most of the metals.
The boiling points of HBr is 124 deg C.
Hydrogen bromide is a colorless gas with a strong smell, highly soluble in water, and significantly dissociated in an aqueous solution.
It easily fumes in moist air.
Hydrogen bromide gases are highly corrosive and can cause severe burns upon contact.
Anhydrous hydrobromic acid is hazardous and is transported in high-pressure cylinders.

Hydroiodic Acid (HI)

Hydroiodic acid is a strong colorless acid.
The chemical formula of Hydroiodic acid is HI.
Hydroiodic acid is aqueous solution of hydrogen iodide.
The boiling point of HI is -35.4 deg C.
The fumes of this acid irritate the eyes and skin and can corrode animal tissues.
The gas hydrogen iodide is non-flammable and can be toxic if inhaled. Inhalation may lead to adverse health effects.

Perchloric Acid (HClO₄)

Perchloric acid is a strong colorless acid.
The chemical formula of perchloric acid is HClO_{4 .}
The boiling point of perchloric acid is 203 deg C.
It is a strong oxidizing agent and corrosive to tissue and metals.
Owing to its strong oxidizing properties, this compound exhibits very high reactivities toward most metals.
It is also known as Hyperchloric acid.
Perchloric acid is used as an oxidizer in the separation of sodium and potassium.
It is Used in making explosives.
It is Used for plating of metals.

What is Weak Acid?

Weak Acid are those acid which dissociates partially in aqueous solution. They dissociates partially in cation and anion when dissolved in aqueous solution.

They do not loose H⁺ ion easily in aqueous solution.
Weak acid has higher pH as compared to Strong acid because they do not dissociate easily into their ions in aqueous solution.
Weak acids are bad conductor of electricity in aqueous solution.

Weak Acid Definition

Weak Acids are defined as the acids which partially dissociates into H⁺and OH^–ion in water

Dissociation of Weak Acids

Weak Acids dissociates partially in aqueous solution while Strong Acids dissociates completely in aqueous solution. The strength of acids depend upon how much it dissociates in aqueous solution. The dissociation of a weak acid can be expressed as follows:

HA⇌ H⁺ + OH^–

where,

HA represents the weak acid molecule.

H⁺ represents a hydrogen ion (proton).

OH^–represents the conjugate base of the weak acid

List of Weak Acids

Weak Acids are the acids that do not completely dissociate into their constituent ions when dissolved in solutions. The pH of Weak acid is about in the range of 3-5. The value of Acid dissociation constant of weak acid is low. Weak acids does not release all H⁺ which are present. The weak acid include Hydrofluoric acid, Nitrous acid, Acetic acid, Sulfurous acid and Phosphoric acid.

Hydrofluoric Acid (HF)

It is a colorless Weak acid.
The chemical formula of Hydrofluoric acid is HF.
The boiling point of HF is 63 deg C.
This acid is also widely used in the preparation of many useful fluorine compounds.
It is an inorganic acid which is colorless and highly corrosive capable of dissolving many substances and compounds like oxides.
The physical properties of the HF, like its density, melting point and boiling point varies because it is dependent on the concentration of HF in the aqueous solution.

Nitrous Acid (HNO₂)

It is pale blue color Weak acid.
The chemical formula of Nitrous acid is HNO₂.
It has pungent smell. The boiling point of HNO₂ is 158 deg C.
Nitrous acid is a mixture of nitric acid and nitrous gas but with a smaller proportion of oxygen than what exists in nitric acid.
Nitrous acid was discovered by Scheele.
It is obtained by distilling perfectly dry nitrate of lead in a retort, fitted with a receiver.

Acetic Acid (CH₃COOH)

It a weakly acidic compound commonly known as vinegar.
The formula of Acetic acid is CH₃COOH.
It has a pungent smell and sour in taste.
These are added in pickels for increasing taste of it and it also act as preservatives.
The boiling point of Acetic acid is 118 deg C.
It is a carboxylic acid consisting of a methyl group that is attached to a carboxyl functional group.
The systematic IUPAC name of acetic acid is ethanoic acid.

Sulfurous Acid (H₂SO₃)

It is a colorless weak acid.
Sulfurous acid is also referred to as Sulfur dioxide solution or trioxosulfuric acid or di-hydrogen trioxosulfate.
It is an intermediate species that forms acid rain from sulfur dioxide (which is SO₂).
There is no evidence that sulfurous acid exists in the solution, but this molecule has been detected in the gaseous phase.
This compound is used as a reducing agent. Sulfurous acid can be used as an intermediate in industries.

Strong Acids vs Weak Acids

The difference between Strong Acid and Weak Acid is tabulated below:

Basis of Comparison	Strong Acids	Weak Acids
Definition	Completely dissociate in aqueous solution	partially dissociate in aqueous solution
pH	pH is lower, less than or equal to 1.	pH is grater than or equal to 2.
Conductivity	Higher Conductivity	Lower Conductivity
Examples	Hydrochloric Acid (HCl), Sulfuric Acid (H₂SO₄), Nitric Acid (HNO₃), Hydroiodic Acid (HI), Perchloric Acid (HClO₄)	Acetic Acid (CH₃COOH), Citric Acid (C₆H₈O₇), Phosphoric Acid (H₃PO₄), Formic Acid (HCOOH)

Table of Strong and Weak Acids

Strong and Weak Acids are mentioned in the table below:

Strong Acids	Weak Acids
Hydrochloric Acid(HCl)	Hydroflouric Acid(HF)
Sulfuric Acid(H₂SO₄)	Phosphoric Acid(H₃PO₄)
Nitric Acid(HNO₃)	Carbonic Acid(H₂CO₃)
Hydrobromic Acid(HBr)	Acetic Acid(CH₃COOH)
Perchloric Acid(HClO₄)	Nitrous Acid(HNO₂)
Hydroiodic Acid(HI)	Hydrocyanic Acid(HCN)

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