Is HBr a Base or an Acid?

Hydrogen bromide has the chemical formula HBr and is an inorganic hydrogen halide compound. It has a strong odour and is colourless. If this gas is inhaled, it can cause hypoxia (suffocation) and irritation. Hydrogen bromide is very water soluble and weights more than air.

We’ll look at whether hydrogen bromide (HBr) is an acid or a base in this article.

Is HBr a basic or an acid? In an aqueous solution, hydrogen bromide (HBr) dissociates into two ions, H+ and Br-, making it an acid. An acid is defined as a substance that releases protons in an aqueous solution. Furthermore, because HBr entirely dissociates in an aqueous solution, it is classified as a strong acid with a pH of 3.01 in 1 mM.

Let’s take a closer look at it. Keep in touch till the very end.

HBr’s pH

Hydrobromic acid (HBr) is a strong acid that completely dissociates into H+ and Br- in water.

The concentration of H+ will be the same as the concentration of HBr since there will be one mole of H+ for every mole of HBr.

The concentration of H+ ions in a 1mM solution of hydrobromic acid will be 1 millimole (0.001 moles) in order to estimate the pH.

The following is the formula for calculating pH:

pH = – log [H+]

Put the value of the concentration of H+ ions as follows to calculate the ph of a compound using the preceding equations.

= − log pH (0.001)

pH = negative (-3)

pH = 3, where a higher pH implies that the substance is more acidic.

Positive, negative, or even zero pH values are possible. When the pH of a 1M HBr solution is determined, -log(1) equals zero, and the solution is classified as a strong acid.

Why is HBr such a powerful acid?

When a strong acid comes into touch with water, it completely dissociates into its ions.

The strong acid is HBr, which totally dissociates in an aqueous solution. The 3-D form of the HBr molecule is shown below.

Theorem of Arrhenius:

We must examine Arrhenius’ famous idea for acidic compounds in order to justify it according to chemical laws.

A material is acidic if it produces H+ ions when dissolved in water and forms H3O+ ions when coupled with the water molecule, according to this theory.

Now you can investigate HBr dissociation in an aqueous solution.

HBr(aq) => H+(aq) + Br-(aq)

When H+ is dissolved in water, it can interact with the H2O molecule to generate hydronium ion (H3O+ ion).

Is HBr an Acid or Base?


Hydrogen Bromide is an inorganic hydrogen halide compound with the molecular formula HBr. It is a colorless gas with a strong odor. Exposure to this gas can cause asphyxia (suffocation) and irritation if inhaled. Hydrogen bromide is highly soluble in water and weighs heavier than air.

In this article, we’ll look at whether Hydrogen bromide (HBr) is an acid or a base.

So is HBr an acid or base? Hydrogen bromide (HBr) is an acid because it dissociates into two ions as H+ and Br- in an aqueous solution. Any compound that releases protons in an aqueous solution is considered to be an acid. Moreover, as HBr completely dissociates in an aqueous solution it is regarded as the strong acid with a pH of 3.01 in 1 mM of an aqueous solution.

Let us study it in detail. Stay Connected till last.

pH of HBr

Hydrobromic acid (HBr) is a powerful acid that will entirely dissociate in water into H+ and Br-.

Because there will be one mole of H+ for every mole of HBr, the concentration of H+ will be the same as the concentration of HBr.

In order to determine the pH of 1mM solution of hydrobromic acid, the concentration will be 1 millimole (0.001 moles) of H+ ions in the solution.

The formula for calculating pH is as follows:

pH = – log [H+]

To calculate the ph of a compound using the above formulae, put the value of the concentration of H+ ions as below.

pH = – log (0.001)

pH = -(-3)

pH = 3 where a pH of 3 indicates that the compound is more acidic in nature.

The pH value can be positive, negative, or even zero. For example, if the pH of 1M of HBr solution is calculated, -log(1) becomes zero and it is also regarded as a strong acid.

pH scale

Why is HBr a Strong Acid?

A strong acid is one that totally dissociates into its ions when it comes into contact with water.

As HBr completely dissociates in an aqueous solution it is regarded as the strong acid. Below is the 3-D shape of the HBr molecule.

HBr Structure

Arrhenius Theory:

In order to justify it according to the laws of chemistry, we have to analyze the famous theory given by Arrhenius for the acidic compounds.

According to this idea, a substance is acidic if it produces H+ ions when dissolved in water and forms H3O+ ions when combined with the water molecule.

Examine HBr dissociation in an aqueous solution now.

HBr(aq) => H+(aq) + Br-(aq)

Sometimes the H+ combines with the H2O molecule when dissolved in water and forms hydronium ion (i.e) H3O+ ion

H+ + H2O => H3O

Furthermore, an acid, according to Arrhenius, is a chemical that raises the concentration of hydrogen ions (H+) in a solution.

When the HBr molecule is dissolved in water, one H+ ion is released, raising the hydrogen ion concentration in the final solution. As a result, the HBr compound meets all of the conditions of the Arrhenius acid compound.

As a result, HBr is an Arrhenius acid compound.

The Bronsted-Lowry Hypothesis:

The Bronsted-Lowry theory is another prominent acid-base theory that needs to be proved.

A substance becomes an acid, according to this theory, when it provides a proton to another species and produces a conjugate base.

A chemical is defined as a base when it receives a proton from another species and forms a conjugate acid.

It gives a proton to another species in the form of a conjugate base in HBr (Br-).

HBr + H2O => H+(aq) + Br-(aq)

HBr + NH3 => NH4 + Br-

Be a result, HBr is referred to as a Bronsted-Lowry acid.

The following qualities must be present in a substance to determine if it is a strong acid:

They must be strong electrolytes with a high conductivity.

Their pH ranges from 1 to 3, and in some cases, 0 and negative.

They dissolve completely, releasing a massive number of H+ ions into the solution.

Because HBr has all of the above qualities, it is classified as a STRONG ACID.

What is HBr’s Conjugate Base?

The Bronsted-Lowry theory of acids and bases includes conjugate acids and bases.

In Bronsted-Lowry theory, an acid is a proton donor, while a base is a proton acceptor. As a result, in the case of HBr, which reacts with water according to the following equation:-

H3O+(aq)   +   Br-   —->    HBr(g)   +   H2O(l) (aq)

Because it has absorbed a proton to form H3O+, water is a Bronsted base, whereas HBr is a Bronsted acid because it has provided the proton.

Because in Brnsted-Lowry theory, a conjugate base is whatever is left over after a proton reacts with a base, the Br- ion is the conjugate base of HBr.

According to a basic rule of thumb, a conjugate base has one less hydrogen atom and one more negative charge than the original acid.

An anion can be thought of as a conjugate base.

Is HBr Acidic Compared to HCl?

The strength of an acid is determined by two factors:

Dissociation degree

The acidity increases as the degree of dissociation increases.

The H–Br bond is bigger than the H–Cl bond in binary acids like HBr and HCl. This is due to Br’s higher atomic size than Cl’s.

Because the H–Br link is weaker than the H–Cl bond, they dissociate rapidly in aqueous solution. Because HBr has a higher degree of dissociation than HCl, it is more powerful.


Furthermore, when atomic size rises, the atom’s electronegativity diminishes. When it comes to acidity,

As we proceed from left to right in the periodic table, the electronegativity of elements increases along the row.

The electronegativity of elements reduces as we travel down the group because atomic size continues to grow.

As a result, Br is less electronegative than Cl in the halides group of atoms. When compared to HCl, HBr is a powerful acid.

Is HBr a basic or an acid?

A Lewis acid molecule is formed when a substance accepts a pair of electrons from another chemical.

A Lewis base compound is one that donates a pair of electrons to another chemical.

HBr is a Lewis acid because it accepts one lone pair of electrons when it combines with a water molecule to generate hydronium ion and Br– conjugate base.

Bromine is more electronegative than hydrogen and has three lone around it, therefore it attracts more electrons, according to the Lewis acid theory with the HBr molecule.

The bromine atom has a negative charge, while the hydrogen atom has a positive charge as a result.

The lone pair on the water molecule (H2O) drew the hydrogen atom somewhat, while the negative charge of the Bromine atom repelled more electrons.

The bromine ion is produced as a result of the development of a coordinating link between oxygen and hydrogen.

As a result, the entire HBr molecule acts as a Lewis acid, accepting the lone pair of electrons from H2O and breaking off the Bromide ion.

The statement that HBr is a lewis acid is supported by the following reasoning.


Elemental bromine is most commonly used as a cleaning or disinfecting agent, as well as a chemical intermediate.

It is utilised as a reagent and a catalyst in a variety of chemical processes.

It’s employed in the production of a wide range of organic compounds.

It’s used as a catalyst in the production of PTA/PET, as an energy storage electrolyte, and as a hydrobromination agent in a range of organic processes (for Pharma and Agro applications).

Hydrogen bromide is a chemical that is used to create pharmaceuticals and chemicals, as well as a solvent and a veterinary medication.

A hydrobromide salt of a synthetic morphine derivative used as an antitussive (cough suppressor).


HBrHydrobromic Acid
Chemical FormulaHBr
Molecular Weight80.9119 g/mol
Density1.49 g/cm³
SolubilitySoluble in water
Boiling Point122 °C
Melting Point-11 °C
OdorPungent irritating odor
AppearanceColorless/faint yellow liquid
Heat capacity29.1 J/(K·mol)

• Anhydrous hydrobromic acid is a poisonous substance that is administered in high-pressure cylinders.

• Hydrobromic acid is non-combustible and non-explosive. At high temperatures, it will generate deadly hydrogen bromide vapours.

• Eyes, skin, and mucous membranes are all corroded by hydrobromic acid.


When dissociated in an aqueous solution, hydrogen bromide is a colourless, pungent-smelling inorganic molecule that releases H+ ions. The above-mentioned Arrhenius, Bronsted-Lowry, and Lewis theories explain and demonstrate that

With a pH of 3, HBr is a strong acid. Furthermore, the steps for calculating pH have been presented with an appropriate example.

The most important takeaways

• When dissolved in water, HBr creates H+ ions, making it acidic.

• It gives another species a proton (H+) and produces a conjugate base (Br-)

• Lewis acid is a chemical that receives a pair of electrons from another one.

I hope that this essay has given you a better understanding of the acidic nature of HBr and its other properties.

Read more: Geometry, Hybridization, and Polarity of CHF3 Lewis Structure

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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