Within the Brønsted-Lowry (protonic) theory of acids and bases, 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. Johannes Nicolaus Brønsted born in Varde ( February 22, 1879 – December 17, 1947) was a Danish physical chemist Thomas Martin Lowry ( October 26, 1874 - November 2, 1936) was an English physical chemist. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive A conjugate acid can also be seen as the chemical substance that releases a proton in the backward chemical reaction. Thus, the term acid. The base produced, X⁻, is called the conjugate base and it absorbs a proton in the backward chemical reaction. In aqueous solution, the chemical reaction involved is of the form

HX + H₂O X⁻ + H₃O⁺

This principle is discussed in detail in the article on acid-base reaction theories.

The conjugate base of a weak acid is a strong base, and the conjugate base of a strong acid is a weak base.

Tabulated below are several examples of conjugate acid-base pairs. Acid strength decreases and base strength increases down the table. (The dissociation reaction reaches equilibrium further to the right, with more X⁻ produced. )

Acid	Base
HCl Hydrochloric acid	Cl− Chloride ion
H2SO4 Sulfuric acid	HSO4− Hydrogen sulfate ion
HNO3 Nitric acid	NO3− Nitrate ion
H3O+ Hydronium ion	H2O Water
HSO4− Hydrogen sulfate ion	SO42− Sulfate ion
H3PO4 Phosphoric acid	H2PO4− Dihydrogen phosphate ion
HC2H3O2 Acetic acid	C2H3O2− Acetate ion
H2CO3 Carbonic acid	HCO3− Hydrogen carbonate ion
H2S Hydrosulfuric acid	HS− Hydrogen sulfide ion
H2PO4− Dihydrogen phosphate ion	HPO42− Hydrogen phosphate ion
NH4+ Ammonium ion	NH3 Ammonia
HCO3− Hydrogencarbonate (bicarbonate) ion	CO32− Carbonate ion
HPO42− Hydrogen phosphate ion	PO43− Phosphate ion
H2O Water (neutral, pH 7)	OH− Hydroxide ion
HFSbF5 Fluoroantimonic acid	SbF5− Antimony pentafluoride ion

See also

• protonation

Hydrochloric acid is the Solution of Hydrogen chloride ( H[[Chlorine Cl]] in water The chloride Ion is formed when the element Chlorine picks up one Electron to form an Anion (negatively-charged ion Cl&minus Sulfuric (or sulphuric acid, H 2 S[[oxygen O]]4 is a strong Mineral acid. Nitric acid ( H[[nitrate NO3]] also known as Aqua fortis and spirit of nitre, is a highly corrosive and In Inorganic chemistry, a nitrate is a salt of Nitric acid with an Ion composed of one Nitrogen and three Oxygen atoms In Chemistry, hydronium is the obsolete name for the Cation H 3 O + derived from Protonation of Water Water ( H2[[oxygen O]] H OH) is the most abundant Molecule on Earth 's surface composing of about 70% of the Earth's surface as Phosphoric acid, also known as orthophosphoric acid or phosphoric(V acid, is a mineral (inorganic acid having the Chemical formula A phosphate, an Inorganic chemical, is a salt of Phosphoric acid. Acetic acid, also known as ethanoic acid, is an organic chemical compound, giving Vinegar its sour taste An acetate, or ethanoate, is either a salt or Ester of Acetic acid. Carbonic acid (ancient name acid of air or aerial acid) has the formula H2CO3 In Inorganic chemistry, bicarbonate ( IUPAC -recommended nomenclature hydrogencarbonate) is an intermediate form in the Deprotonation Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. A phosphate, an Inorganic chemical, is a salt of Phosphoric acid. A phosphate, an Inorganic chemical, is a salt of Phosphoric acid. Ammonium is also an old name for the Siwa Oasis in western Egypt. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor In Inorganic chemistry, bicarbonate ( IUPAC -recommended nomenclature hydrogencarbonate) is an intermediate form in the Deprotonation In Chemistry, a carbonate is a salt or Ester of Carbonic acid. A phosphate, an Inorganic chemical, is a salt of Phosphoric acid. A phosphate, an Inorganic chemical, is a salt of Phosphoric acid. Water is a common Chemical substance that is essential for the survival of all known forms of Life. pH is the measure of the acidity or alkalinity of a Solution. In Chemistry, hydroxide is the most common name for the diatomic Anion OH− consisting of Oxygen and Hydrogen Fluoroantimonic acid HSbF6 is a mixture of Hydrogen fluoride and Antimony pentafluoride in various ratios Antimony pentafluoride is the Chemical compound with the formula Sb[[Fluorine F]]5 In chemistry protonation is the addition of a proton ( H[[Cation +]] to an Atom, Molecule, or Ion.

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