What is the Brønsted–Lowry theory of acids and bases?

The Brønsted–Lowry theory defines acids as substances that donate protons (H⁺ ions) and bases as substances that accept protons. This theory is fundamental in understanding acid-base equilibria in AS-Level Physical Chemistry, particularly within the Cambridge International A Levels curriculum.

How does the Brønsted–Lowry theory differ from the Arrhenius theory?

While the Arrhenius theory defines acids and bases in terms of their ability to produce H⁺ and OH⁻ ions in water, the Brønsted–Lowry theory broadens this definition by focusing on proton transfer, making it applicable to a wider range of chemical reactions, including those not occurring in aqueous solutions.

Can you give an example of a Brønsted–Lowry acid-base reaction?

A classic example is the reaction between ammonia (NH₃) and water (H₂O). In this reaction, NH₃ acts as a Brønsted–Lowry base by accepting a proton from H₂O, which acts as a Brønsted–Lowry acid. This results in the formation of NH₄⁺ and OH⁻ ions.

What is a conjugate acid-base pair in the Brønsted–Lowry theory?

In the Brønsted–Lowry theory, a conjugate acid-base pair consists of two species that transform into each other by the gain or loss of a proton. For example, in the reaction of acetic acid (CH₃COOH) with water, CH₃COOH and CH₃COO⁻ form a conjugate acid-base pair.

Why is the Brønsted–Lowry theory important for understanding equilibria in chemistry?

The Brønsted–Lowry theory is crucial for understanding chemical equilibria because it explains how acids and bases interact in reversible reactions. This understanding helps predict the direction of equilibrium shifts and the relative strengths of acids and bases, which are key concepts in AS-Level Physical Chemistry under the Cambridge International A Levels curriculum.

Brønsted–Lowry theory of acids and bases Revision Notes & Practice Questions | Cambridge International A Levels Chemistry

Study Notes

The Brønsted–Lowry theory defines acids as proton donors and bases as proton acceptors. Acids increase the concentration of H+ ions in solution, while bases decrease it.

Acid — A substance that donates protons (H+ ions) in a solution. Example: Hydrochloric acid (HCl) donates H+ ions in water.
Base — A substance that accepts protons (H+ ions) in a solution. Example: Sodium hydroxide (NaOH) accepts H+ ions in water.
Strong Acid — Completely dissociates in aqueous solution to release ions. Example: Sulfuric acid (H2SO4) fully dissociates in water.
Weak Acid — Partially dissociates in aqueous solution to release ions. Example: Ethanoic acid (CH3COOH) partially dissociates in water.
Strong Base — Fully dissociates in aqueous solution to release OH- ions. Example: Potassium hydroxide (KOH) fully dissociates in water.
Weak Base — Partially dissociates in aqueous solution to release OH- ions. Example: Ammonia (NH3) partially dissociates in water.
Neutralization Reaction — Reaction where H+ and OH- ions form water. Example: HCl reacting with NaOH to form water and salt.

Exam Tips

Key Definitions to Remember

Acid: Proton donor
Base: Proton acceptor
Strong Acid: Completely dissociates in solution
Weak Acid: Partially dissociates in solution
Strong Base: Fully dissociates in solution
Weak Base: Partially dissociates in solution

Common Confusions

Strong vs. concentrated: Strong refers to dissociation, concentrated refers to amount
Weak vs. dilute: Weak refers to partial dissociation, dilute refers to low concentration

Typical Exam Questions

What is a Brønsted–Lowry acid? A substance that donates protons (H+ ions).
How does a strong acid differ from a weak acid? A strong acid completely dissociates in solution, while a weak acid only partially dissociates.
What happens during a neutralization reaction? H+ ions react with OH- ions to form water.

What Examiners Usually Test

Understanding of acid and base definitions
Differences between strong and weak acids/bases
Ability to explain neutralization reactions

Brønsted–Lowry theory of acids and bases

Notes & worked examples

Study Notes & Exam Tips

Study Notes

Exam Tips

Practice questions

AI-marked quiz

Assess your understanding

Video lesson

Brønsted–Lowry theory of acids and bases — frequently asked questions

Brønsted–Lowry theory of acids and bases

Notes & worked examples

Study Notes & Exam Tips

Exam Tips and Study Notes for Brønsted–Lowry theory of acids and bases

Study Notes

Exam Tips

Practice questions

AI-marked quiz

Assess your understanding

Video lesson

Video Library for Brønsted–Lowry theory of acids and bases

Brønsted–Lowry theory of acids and bases — frequently asked questions

Frequently Asked Questions about Brønsted–Lowry theory of acids and bases

What is the Brønsted–Lowry theory of acids and bases?

How does the Brønsted–Lowry theory differ from the Arrhenius theory?

Can you give an example of a Brønsted–Lowry acid-base reaction?

What is a conjugate acid-base pair in the Brønsted–Lowry theory?

Why is the Brønsted–Lowry theory important for understanding equilibria in chemistry?