The Bronsted-Lowry theory of acids and bases was first proposed in 1923. The fundamental concept behind this theory is the idea that an acid and a base react with each other and cause the acid to form a conjugate base, while the base forms a conjugate acid. This is done because of the exchange of a proton during the process.
This theory is considered a generalization and an expansion of the Arrhenius theory.
Defining Acids and Bases
In the Arrhenius theory, acids are a substance that disassociates a solution in order to give a hydrogen ion. Bases dissociate and give hydroxide ions. Neutralization occurs when the two meat because hydrogen and hydroxide ions react together to produce water.
Johannes Bronsted and Thomas Lowry, working independently of one another in Denmark and England respectively, both independently proposed the idea that acids and bases are defined by the way they react with one another. It is a generalized equation that supports an equilibrium because the reaction described in the Bronsted Lowry theory can move both forward and backward.
Bronsted was born in 1879 and worked as a physical chemist. He earned a degree in chemicall engineering and then a PhD in 1908 from the University of Copenhagen. He published his first paper on electron affinity in 1906.
Lowry was born in 1874 and was also a physical chemist. His family was Cornish and his father was a local reverend. He earned his degree at Central Technical Collecge and was a founding member of the Faraday Society. Lowry would be made a teacher of chemistry in a medical school at a University Professor at the University of London. Lowry also served as the Chair of Physical Chemistry at Cambridge.
Limitations on the Theory
There are certain limitations that are placed on the theory of acids and bases. Hydrocholoric acid, for example, can be neutralized by ammonia in addition to sodium hydroxide. Both reactions create a colorless solution that crystalizes into a chloride. It creates a reaction with equilibrium, but eliminates the idea that there is specificity within the theory of transfer.
This is why both Bronsted and Lowry looked at acids and bases in a different way. Acids became “donors” and bases became “acceptors.” This allowed their theory to add to the original Arrhenius theory about acids and bases.
When hydrogen chloride gas is able to dissolve in water, it produces hydrochloric acid. This causes the hydrogen chloride molecule to give a proton to the water molecule. This forms a dative covalent between one of the lone pairs on the oxygen and the hydrogen so that hydroxonium ions are then produced.
Then, when an acid in a solution reacts with a base, what is functioning in this equation as the acid is really a hydroxonium ion. When a proton is transferred during this process, it is causing a hydroxonium ion to work with a hydroxide ion and this makes water.
This eliminates the hydrogen chloride and ammonia problem that was originally in the theory of acids and bases. When you look at a reaction in a solution or within a gaseous state, ammonia becomes a base because it is able to accept a hydrogen ion. This ion becomes attached to the lone pair on the nitrogen atom within ammonia through a coordinate bond.
Amphoteric Substances and the Bronsted Lowry Theory
At the heart of the Bronsted Lowry theory of acids and basis is the idea that an acid will only exist as such in relation to a base, with a base operating the same way in relation to an acid. Water, however, is amphoteric because it acts as both an acid and a base. This is why many of the components described within the theory involve solutions that are non-aqueous in nature.
Yet the Bronsted Lowry theory is often considered to be incomplete. In the same year they proposed their theory, G.N. Lewis proposed an expansion of it. The Lewis theory is based on electronic structures instead, creating what is known as a Lewis acid and a Lewis base. In this theory expansion, a Lewis base can donate an electron pair, not a single ion, to a Lewis acid, and the reverse is also true.
This allows the Bronsted Lowry theory to have an explanation for their terms of electronic structure within the equation of equilibrium.
The Bronsted Lowry theory of acids and bases has advanced science in numerous ways and it is a theory that is still commonly used today.