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Protic Acid vs. Lewis Acid: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on January 4, 2024
Protic acids can donate protons (H⁺), while Lewis acids accept electron pairs; protic acids involve H⁺ transfer, Lewis acids involve electron pair acceptance.

Key Differences

Protic acids, like hydrochloric acid, have a hydrogen atom which can be donated as a proton in chemical reactions. In contrast, Lewis acids, such as aluminum chloride, accept electron pairs but do not necessarily donate protons.
The strength of a protic acid is measured by its ability to donate a proton, with sulfuric acid being a strong example. Lewis acids, on the other hand, are characterized by their electron-pair accepting ability, like in the case of boron trifluoride.
Common examples of protic acids include water and acetic acid, which are part of many biological and chemical processes. Lewis acids, like ferric chloride, are often used as catalysts in organic synthesis.
Protic acids are typically involved in acid-base reactions in aqueous solutions. Lewis acids, however, are crucial in complexation reactions, where they accept electron pairs from Lewis bases.
The concept of protic acids is central in the Brønsted-Lowry acid-base theory. Lewis acids, conversely, are defined by the Lewis theory of acids and bases, focusing on electron pairs.

Comparison Chart


Donates protons (H⁺)
Accepts electron pairs

Key Examples

Hydrochloric acid, acetic acid
Aluminum chloride, boron trifluoride

Acid Strength Criterion

Ability to donate a proton
Ability to accept an electron pair

Common Reactions

Acid-base reactions in aqueous solutions
Complexation reactions, often as catalysts

Theoretical Basis

Brønsted-Lowry theory
Lewis theory of acids and bases

Protic Acid and Lewis Acid Definitions

Protic Acid

A substance with a hydrogen atom that can be released as a proton.
Water acts as a weak protic acid in some reactions.

Lewis Acid

An electron-pair acceptor in chemical reactions.
In the reaction, the Lewis acid accepted electrons from the base.

Protic Acid

A proton donor in chemical processes.
In the reaction, ammonia received a proton from the protic acid.

Lewis Acid

A substance that can accept a pair of electrons to form a coordinate covalent bond.
Boron trifluoride is a classic example of a Lewis acid.

Protic Acid

A hydrogen-containing acid participating in acid-base reactions.
Acetic acid is a common protic acid in vinegar.

Lewis Acid

A chemical entity involved in complexation reactions.
The Lewis acid formed a complex with the Lewis base.

Protic Acid

An acid capable of donating a proton.
Hydrochloric acid is a strong protic acid.

Lewis Acid

A compound that accepts an electron pair.
Aluminum chloride functions as a Lewis acid in many reactions.

Protic Acid

An acid that contributes protons to the reaction environment.
Sulfuric acid is a protic acid used in industrial processes.

Lewis Acid

A catalyst in organic reactions by accepting electron pairs.
Iron(III) chloride is used as a Lewis acid in synthesis.


What is a Lewis acid?

A compound that accepts electron pairs.

Are all Lewis acids also protic acids?

No, Lewis acids may not donate protons.

Is water a protic acid?

Yes, it can donate a proton.

What is a protic acid?

An acid that donates protons.

Is BF₃ a Lewis acid?

Yes, it accepts electron pairs.

Are protic acids always liquids?

No, they can be in various states.

Can Lewis acids be gases?

Yes, they can exist in different states.

How do protic acids affect pH?

They lower pH by increasing H⁺ concentration.

Can protic acids act as Lewis acids?

Yes, if they accept electron pairs.

Do Lewis acids change pH?

Not directly, they don't donate H⁺.

Can protic acids be weak?

Yes, like acetic acid.

Can Lewis acids be used in polymerization?

Yes, as catalysts.

Is AlCl₃ a strong Lewis acid?

Yes, it's a potent electron pair acceptor.

Are Lewis acids limited to certain reactions?

They're versatile but common in complexation and catalysis.

Is HCl a strong protic acid?

Yes, it readily donates protons.

Are all protic acids corrosive?

Many are, but not all.

What's a common use for protic acids?

In food and chemical industries.

Do Lewis acids have industrial uses?

Yes, especially in catalysis.

Are Lewis acids involved in acid-base reactions?

They're involved in complexation reactions.

Do protic acids always contain hydrogen?

Yes, in a form that can be donated.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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