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Chemistry · Ch 3 — Ionic Equilibria

Bronsted - Lowry theory

3.3.2

Bronsted - Lowry theory

J. N. Bronsted and T. M. Lowry (1923) proposed a more general theory known as the Bronsted-Lowry proton transfer theory. According to this theory acids and bases are defined as follows.

Acid : Acid is a substance that donates a proton (H+\mathrm{H^{+}}) to another substance.

Base : Base is a substance that accepts a proton (H+\mathrm{H^{+}}) from another substance.

For example :

HClAcid1+NH3Base2⇌NH4+Acid2+Cl−Base1\underset{\text{Acid}_1}{\mathrm{HCl}} + \underset{\text{Base}_2}{\mathrm{NH_3}} \rightleftharpoons \underset{\text{Acid}_2}{\mathrm{NH_4^{+}}} + \underset{\text{Base}_1}{\mathrm{Cl^{-}}}

In the above reaction HCl and NH4+\mathrm{NH_4^{+}} are proton donors and act as acids. The NH3\mathrm{NH_3} and Cl−\mathrm{Cl^{-}} are proton acceptors and act as bases. Further it follows that the products of the Bronsted-Lowry acid-base reactions are acids and bases. …

Figure conjugate-pairAnnotated Bronsted-Lowry equation for hydrochloric acid reacting with water, with Acid-1, Base-2, Acid-2 and Base-1 role labels beneath the four species and two bracket connectors marking conjugate acid-base pair 1 (HCl and Cl-) and conjugate acid-base pair 2 (H2O and H3O+).
Fig. conjugate-pair — Annotated Bronsted-Lowry equation for hydrochloric acid reacting with water, with Acid-1, Base-2, Acid-2 and Base-1 role labels beneath the four species and two bracket connectors marking conjugate acid-base pair 1 (HCl and Cl-) and conjugate acid-base pair 2 (H2O and H3O+).

Drawn by us to help you understand the concept clearly, and verified to make sure it's accurate. For exams, practice from your textbook's own diagram.

What this diagram shows. The reaction HCl(aq)+H2O(l)⇌H3O+(aq)+Cl−(aq)\mathrm{HCl(aq)} + \mathrm{H_2O}(l) \rightleftharpoons \mathrm{H_3O^{+}(aq)} + \mathrm{Cl^{-}(aq)} with every species labelled by its Bronsted-Lowry role -- Acid1_1 under HCl, Base2_2 under H2_2O, Acid2_2 under H3_3O+^{+} and Base1_1 under Cl−^{-}. The inner connector joins Base2_2 and Acid2_2 as conjugate acid-base pair2_2 (water gains a proton to become hydronium); the longer outer connector joins Acid1_1 and Base1_1 as conjugate acid-base pair1_1 (HCl loses a proton to become Cl−^{-}). Each pair dif …

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