In 1923 chemists Johannes Nicolaus Brønsted and Thomas Martin Lowry independently recognized that acid-base reactions involve the transfer of a proton.

According to Brønsted – Lowry acid-base theory, acids are substances that donate a positive hydrogen ion to another substance in a chemical reaction ; by extension, a base is the substance which receives that hydrogen ion.

This led in 1923 to his formulation of the protonic definition of acids and bases, now known as Brønsted – Lowry acid-base theory, independently of the work by Johannes Nicolaus Brønsted.

Within the Brønsted – Lowry acid-base theory ( protonic ), a conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton ( hydrogen ion ).

: for the non-specific Brønsted acid-base reaction:

In chemistry, the Brønsted – Lowry theory is an acid-base theory, proposed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923.

Specific and general catalysis is also found in base catalysed reactions and base Brønsted equation also exists with constant β.

All Brønsted acids are also Lewis acids, but not all Lewis acids are Brønsted acids.

Although zinc chloride solutions are acidic by the Brønsted definition, the zinc cation also specifically attacks hydroxyl groups as a Lewis acid.

As Brønsted – Lowry bases are proton acceptors, a weak base may also be defined as a chemical base in which protonation is incomplete.

In this system, Brønsted acids and Brønsted bases are defined, by which an acid is a molecule or ion that is able to lose, or " donate ," a hydrogen cation ( proton, H < sup >+</ sup >), and a base is a species with the ability to gain, or " accept ," a hydrogen cation ( proton ).

but here very few protons are exchanged since the Brønsted – Lowry acidity of the aqua ion is negligible ( K < sub > a </ sub > = 3. 0 × 10 < sup >- 12 </ sup >).

The strongest superacids are prepared by the combination of two components, a strong Lewis acid and a strong Brønsted acid.

Enolates can exist in quantitative amounts in strictly Brønsted acid free conditions, since they are generally very basic.

The general reaction scheme is shown below, showcasing the utilization of a Brønsted base as the activating agent as opposed to fluoride, phosphine ligands are also used on the metal center.

A Brønsted-Lowry acid ( or simply Brønsted acid ) is a species that donates a proton to a Brønsted-Lowry base.

Both theories easily describe the first reaction: CH < sub > 3 </ sub > COOH acts as an Arrhenius acid because it acts as a source of H < sub > 3 </ sub > O < sup >+</ sup > when dissolved in water, and it acts as a Brønsted acid by donating a proton to water.

This reaction cannot be described in terms of Brønsted theory because there is no proton transfer.

A proton is transferred from an unspecified Brønsted acid to ammonia, a Brønsted base ; alternatively, ammonia acts as a Lewis base and transfers a lone pair of electrons to form a bond with a hydrogen ion.

Brønsted and Lowry generalised this further to a proton exchange reaction:

The Brønsted – Lowry definition applies to other solvents, such as dimethyl sulfoxide: the solvent S acts as a base, accepting a proton and forming the conjugate acid SH < sup >+</ sup >.

The ammonium ion is generated when ammonia, a weak base, reacts with Brønsted acids ( proton donors ):

A Lewis base, defined as an electron-pair donor, can act as a Brønsted – Lowry base as the pair of electrons can be donated to a proton.

Boric acid also exemplifies the usefulness of the Brønsted – Lowry concept for an acid that does not dissociate but does effectively donate a proton to the base, water.

The water molecule in turn donates a proton to a second water molecule and, therefore, acts as a Brønsted acid.

Another method of termination, chain transfer, can occur when an agent can act as a Brønsted acid.

* Chemistry: Molecular theory — Kinetic theory of gases — Molecular orbital theory — Valence bond theory — Transition state theory — RRKM theory — Chemical graph theory — Flory-Huggins solution theory — Marcus theory — Lewis theory ( successor to Brønsted – Lowry acid – base theory ) — HSAB theory — Debye – Hückel theory — Thermodynamic theory of polymer elasticity — Reptation theory — Polymer field theory — Møller – Plesset perturbation theory — Density Functional Theory — Frontier molecular orbital theory — Polyhedral skeletal electron pair theory — Baeyer strain theory — Quantum theory of atoms in molecules — Collision theory — Ligand field theory ( successor to Crystal field theory ) — Variational Transition State Theory — Benson group increment theory — Specific ion interaction theory

The other metal oxides and hydroxides mentioned above also function as Lewis acids rather than Brønsted acids.

Some Lewis acids, defined as electron-pair acceptors, also act as Brønsted – Lowry acids.

However not all Lewis acids generate Brønsted – Lowry acidity.

The reaction can be catalyzed by Brønsted acids and / or by Lewis acids such as boron trifluoride.

More recent IUPAC recommendations now suggest the newer term " hydronium " be used in favor of the older accepted term " oxonium " to illustrate reaction mechanisms such as those defined in the Brønsted – Lowry and solvent system definitions more clearly, with the Arrhenius definition serving as a simple general outline of acid – base character.

In 1923, Johannes Nicolaus Brønsted and Martin Lowry published essentially the same theory about how acids and bases behave, using an electrochemical basis.

* 1879 – Johannes Nicolaus Brønsted, Danish physical chemist ( d. 1947 )

Independently from Johannes Nicolaus Brønsted he has developed the Brønsted – Lowry acid – base theory and was as a founder-member and president ( 1928 – 1930 ) of the Faraday Society.

* February 22 – J. N. Brønsted, Danish chemist ( d. 1947 )

In reaction with water or Brønsted acids the highly toxic and explosive hydrogen azide is released.

* February 22-J. N. Brønsted ( died 1947 ), Danish physical chemist.

Note that chemists often write H < sup >+</ sup >( aq ) and refer to the hydrogen ion when describing acid-base reactions but the free hydrogen nucleus, a proton, does not exist alone in water, it exists as the hydronium ion, H < sub > 3 </ sub > O < sup >+</ sup >.

A third concept was proposed in 1923 by Gilbert N. Lewis which includes reactions with acid-base characteristics that do not involve a proton transfer.

Contrast the following reactions which could be described in terms of acid-base chemistry.

The Brønsted-Lowry definition is the most widely used definition ; unless otherwise specified acid-base reactions are assumed to involve the transfer of a proton ( H < sup >+</ sup >) from an acid to a base.

The acid dissociation constant K < sub > a </ sub > is generally used in the context of acid-base reactions.

Examples of polyatomic ions that do not split up during acid-base reactions are hydroxide ( OH < sup >−</ sup >) and phosphate ( PO < sub > 4 </ sub >< sup > 3 −</ sup >).

This type of reaction occurs, for example, in redox and acid-base reactions.

In redox reactions, the transferred particle is an electron, whereas in acid-base reactions it is a proton.

Acid-base reactions can have different definitions depending on the acid-base concept employed.

In organic chemistry, in addition to oxidation, reduction or acid-base reactions, a number of other reactions can take place which involve covalent bonds between carbon atoms or carbon and heteroatoms ( such as oxygen, nitrogen, halogens, etc .).

Hydrogen plays a particularly important role in acid-base chemistry with many reactions exchanging protons between soluble molecules.

An example of this might be a corrosive acid that is neutralized with a basic substance so that it is no-longer corrosive ( see acid-base reactions ).

It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions.

Inks which are developed by a chemical reaction may depend on an acid-base reaction ( like litmus paper ), reactions similar to the blueprint process, or any of hundreds of others.

The equation is also useful for estimating the pH of a buffer solution and finding the equilibrium pH in acid-base reactions ( it is widely used to calculate the isoelectric point of proteins ).

Protonation and deprotonation occur in most acid-base reactions ; they are the core of most acid-base reaction theories.