What is left after an acid has donated its proton?

1. Losing a proton leaves a species one hydrogen ion short of the original acid. 2. That species is called the conjugate base of the acid. 3. It counts as a base because it can take the proton back and re-form the acid. 4. So HF gives the fluoride ion, and sulfuric acid gives the hydrogensulfate ion. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.1 Brønsted-Lowry Acids and Bases_