Brønsted–Lowry acid–base theory

In the Arrhenius theory, acids are defined as substances that dissociate in aqueous solutions to give H+ (hydrogen ions or protons), while bases are defined as substances that dissociate in aqueous solutions to give OH− (hydroxide ions).

[4] In 1923, physical chemists Johannes Nicolaus Brønsted in Denmark and Thomas Martin Lowry in England both independently proposed the theory named after them.

With an acid, HA, the equation can be written symbolically as: The equilibrium sign, ⇌, is used because the reaction can occur in both forward and backward directions (is reversible).

[10] Some non-aqueous solvents can behave as bases, i.e. accept protons, in relation to Brønsted–Lowry acids.

Because DMSO accepts protons more strongly than H2O the acid becomes stronger in this solvent than in water.

An extreme case occurs with carbon acids, where a proton is extracted from a C−H bond.

Lewis later wrote "To restrict the group of acids to those substances that contain hydrogen interferes as seriously with the systematic understanding of chemistry as would the restriction of the term oxidizing agent to substances containing oxygen.

[16] The reaction above illustrates that BF3 is an acid in both Lewis[17] and Brønsted–Lowry classifications and shows that the theories agree with each other.

On the other hand, magnesium oxide acts as a base when it reacts with an aqueous solution of an acid.

[19] According to the Lux–Flood theory, oxides like MgO and SiO2 in the solid state may be called acids or bases.