Conjugate acid

In 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. The base produced, X^-, is called the conjugate base.

Acid	Base
HCL Hydrochloric acid	Cl- Chlorine ion
H₂SO₄ Sulfuric acid	HSO₄^- Hydrogen sulfate[?] ion
HNO₃ Nitric acid	NO₃^- Nitrate ion
H₃O⁺ Hydronium ion[?]	H₂O Water
HSO₄^- Hydrogen sulfate ion[?]	SO₄^2- 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^-
H₂PO₄^- Dihydrogen phosphate[?] ion	HPO₄⁺ Hydrogen phosphate[?] ion
NH₄⁺ Ammonium ion	NH₃ Ammonia
HCO₃^- Hydrogen carbonate[?] ion	CO₃^2- Carbonate ion
HPO₄^2- Hydrogen phosphate[?] ion	PO₄^3- Phosphate ion
H₂O Water	OH^- Hydroxide ion

Strength of Conjugate Acid-Base Pairs. Acid strength decreases and base strength increases down the table.