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[?]	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-
H2PO4- Dihydrogen phosphate[?] ion	HPO4+ Hydrogen phosphate[?] ion
NH4+ Ammonium ion	NH3 Ammonia
HCO3- Hydrogen carbonate[?] ion	CO32- Carbonate ion
HPO42- Hydrogen phosphate[?] ion	PO43- Phosphate ion
H2O Water	OH- Hydroxide ion

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