conjugate base: substance formed when an acid loses a hydrogen ion Conjugate base of HSO4- is SO42- conjugate acid: substance formed when a base gains a hydrogen ion. Conjugate acid of HSO4- is H2SO4 Solution conjugate base: substance formed when an acid loses a hydrogen ion Conjugate base of HSO4- is SO42- conjugate acid: substance formed when a base gains a hydrogen ion. Conjugate acid of HSO4- is H2SO4.