Arrheniues theory
Lowry-Brönsted theory
Arrhenius theory and Lowry-Brönsted theory are two different approaches to understanding acids and bases.
The Arrhenius theory, developed by Svante Arrhenius in the late 19th century, defines acids as substances that produce hydrogen ions (H+) when dissolved in water, and bases as substances that produce hydroxide ions (OH-) when dissolved in water. According to this theory, acid-base reactions occur when hydrogen ions from an acid combine with hydroxide ions from a base to form water.
The Lowry-Brönsted theory, proposed by Thomas Lowry and Johannes Brönsted in the early 20th century, takes a broader view of acids and bases. According to this theory, an acid is a substance that donates a proton (H+) in a reaction, while a base is a substance that accepts a proton in a reaction. This theory allows for the understanding of acid-base reactions that may not involve water as the solvent and can explain reactions in non-aqueous systems.
In summary, the Arrhenius theory focuses on the role of hydrogen and hydroxide ions in aqueous solutions, while the Lowry-Brönsted theory considers any substance that can donate or accept a proton as an acid or base, regardless of the solvent.
Arrhenius Theory:
1. Definition: The Arrhenius theory, proposed by Svante Arrhenius in 1887, defines an acid as a substance that releases hydrogen ions (H+) in aqueous solution, and a base as a substance that releases hydroxide ions (OH-) in aqueous solution.
2. Acid: According to the Arrhenius theory, when an acid dissolves in water, it dissociates to release hydrogen ions. For example, when hydrochloric acid (HCl) dissolves in water, it forms H+ ions and chloride ions (Cl-).
3. Base: Similarly, a base according to the Arrhenius theory is a substance that releases hydroxide ions in water. For example, when sodium hydroxide (NaOH) dissolves in water, it forms Na+ ions and OH- ions.
4. Acid-Base Reaction: According to the Arrhenius theory, an acid-base reaction occurs when the hydrogen ions from the acid react with the hydroxide ions from the base to form water and a salt. For example, when hydrochloric acid reacts with sodium hydroxide, it forms water (H2O) and sodium chloride (NaCl).
Lowry-Brönsted Theory:
1. Definition: The Lowry-Brönsted theory, proposed by Thomas Lowry and J.N. Brönsted in 1923, defines an acid as a substance that donates a proton (H+) in a chemical reaction, and a base as a substance that accepts a proton.
2. Acid: According to the Lowry-Brönsted theory, an acid is a substance that donates a proton to another species. For example, when hydrochloric acid (HCl) donates a proton, it becomes a chloride ion (Cl-) after losing its hydrogen atom.
3. Base: A base, according to the Lowry-Brönsted theory, is a substance that accepts a proton from another species. For example, in the reaction between hydrochloric acid and ammonia (NH3), NH3 acts as a base by accepting the proton from HCl to form the ammonium ion (NH4+).
4. Acid-Base Reaction: In the Lowry-Brönsted theory, an acid-base reaction occurs when a proton transfer takes place between an acid and a base. The acid donates a proton, and the base accepts it. For example, in the reaction between hydrochloric acid and ammonia, HCl donates a proton to ammonia, forming the ammonium ion and chloride ion.
Note: The Lowry-Brönsted theory is more general than the Arrhenius theory because it applies to reactions that do not involve water as the solvent.