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Bronsted-Lowry Theory-Definition, Examples, and Limitations

October 10, 2023
written by Adeel abbas

The Bronsted-Lowry theory proposes that acids donate a proton (H+) to a base, while bases donate a proton to an acid. Understanding the Bronsted-Lowry theory helps explain the nature of acid-base reactions and the properties of acids and bases.

What is Bronsted-Lowry Theory?

Bronsted-Lowry theory is a concept that explains the behavior of acids and bases in chemical reactions. It was proposed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923. This theory is a generalization of the Arrhenius theory of acids and bases.

Bronsted-Lowry Acid

A Bronsted-Lowry acid is a chemical species that can donate a proton (H+ ion). When an acid donates a proton, it forms the conjugate base.

Examples of Bronsted-Lowry Acid

Some examples of Bronsted-Lowry acids are:

Hydrochloric acid (HCl) – When HCl dissociates in water, it donates an H+ ion and forms the chloride ion (Cl).

HCl ⇌ H+ + Cl

Acetic acid (CH3COOH) – Acetic acid donates an H+ ion to form an acetate ion (CH3COO-). CH3COOH ⇌ H+ + CH3COO

Ammonium ion (NH4+) – Ammonium ion donates a proton to form ammonia (NH3).

NH4+ ⇌ H+ + NH3

Bronsted-Lowry Base

A Bronsted-Lowry base is a chemical species that can accept a proton (H+ ion). When a base accepts a proton, it forms the conjugate acid.

Examples of Bronsted-Lowry Base

Some examples of Bronsted-Lowry bases are:

Water (H2O) – Water accepts a H+ ion to form a hydronium ion (H3O+).

H2O + H+ ⇌ H3O+

Hydroxide ion (OH) – Hydroxide ion accepts a proton to form water.

OH + H+ ⇌ H2O

Carbonate ion (CO32-)Carbonate ion accepts a proton to form bicarbonate (HCO3).

CO32- + H+ ⇌ HCO3

Strength of Bronsted-Lowry Acid and Base

The strength of an acid or base depends on how easily it gives up or accepts a proton. Strong acids and bases completely dissociate in water, while weak acids and bases only partially dissociate.

Strong Acids

  • Hydrochloric acid (HCl) – dissociates nearly 100% in water
  • Nitric acid (HNO3)
  • Sulfuric acid (H2SO4)

These strong acids readily donate their protons to water molecules to form hydronium ions (H3O+).

Weak Acids

  • Acetic acid (CH3COOH) – only partially dissociates in water
  • Carbonic acid (H2CO3)
  • Ammonium ion (NH4+)

These weak acids only slightly donate protons to water, resulting in a small amount of hydronium ion formation.

Strong Bases

These ionic compounds completely dissociate in water to produce hydroxide ions (OH) that readily accept protons.

Weak Bases

  • Ammonia (NH3)
  • Phosphate ion (PO43-)
  • Carbonate ion (CO32-)

These bases only partially accept protons from water, resulting in a relatively small amount of conjugate acid formation.

Bronsted-Lowry Acids and their Conjugated Bases

Here are some Bronsted-Lowry Acids and their Conjugated Bases.

Bronsted-Lowry AcidConjugated Base
Hydrochloric acid (HCl)Chloride ion (Cl)
Sulfuric acid (H2SO4)Hydrogen sulfate ion (HSO4)
Nitric acid (HNO3)Nitrate ion (NO3)
Acetic acid (CH3COOH)Acetate ion (CH3COO)
Hydrofluoric acid (HF)Fluoride ion (F)
Hydrobromic acid (HBr)Bromide ion (Br)
Perchloric acid (HClO4)Perchlorate ion (ClO4)
Hydroiodic acid (HI)Iodide ion (I)
Hydrocyanic acid (HCN)Cyanide ion (CN)
Hypochlorous acid (HClO)Hypochlorite ion (ClO)
Nitrous acid (HNO2)Nitrite ion (NO2)
Sulfurous acid (H2SO3)Hydrogen sulfite ion (HSO3)
Phosphoric acid (H3PO4)Dihydrogen phosphate ion (H2PO4)
Carbonic acid (H2CO3)Hydrogencarbonate ion (HCO3)
Ascorbic acid (C6H8O6)Ascorbate ion (C6H7O6)
Citric acid (C6H8O7)Citrate ion (C6H7O7)
Tartaric acid (C4H6O6)Tartrate ion (C4H5O6)
Benzoic acid (C7H6O2)Benzoate ion (C7H5O2)
Oxalic acid (C2H2O4)Oxalate ion (C2HO4)
Salicylic acid (C7H6O3)Salicylate ion (C7H5O3)
Phenol (C6H5OH)Phenoxide ion (C6H5O)
Methanesulfonic acid (CH3SO3H)Methanesulfonate ion (CH3SO3)
Trifluoromethanesulfonic acid (CF3SO3H)Trifluoromethanesulfonate ion (CF3SO3)
Tosic acid (C7H7SO3H)Tosilate ion (C7H7SO3)
Lactic acid (C3H6O3)Lactate ion (C3H5O3)
Formic acid (HCOOH)Formate ion (HCOO)

Limitation of Bronsted-Lowry Theory

  • It focuses only on proton transfer reactions and does not account for other types of acid-base reactions. For example, the reaction of a metal oxide with an acid does not involve proton transfer.
  • It treats all protons as identical, even though the reactivity of a proton depends on its chemical environment. For example, a proton bonded to fluorine in HF is more acidic than a proton bonded to oxygen in H2O.
  • It uses an arbitrary distinction between acids/bases and their conjugates. For example, H2O can act as both an acid (proton donor) and a base (proton acceptor).
  • It does not provide quantitative information about acid or base strength. Other theories like the Lewis theory and solvent system theory aim to account for these limitations.
  • It focuses on reactions in aqueous solutions and does not describe acid-base behavior in non-aqueous solvents very well.
  • The theory treats lone electron pairs as bases, but some lone pairs have little basicity, like the lone pairs on O2.