<P> The strength of an acid refers to its ability or tendency to lose a proton (H). A strong acid is one that completely ionizes (dissociates) in a solution (provided there is sufficient solvent). In water, one mole of a strong acid HA dissolves yielding one mole of H (as hydronium ion H O and higher aggregates) and one mole of the conjugate base, A. Essentially, none of the non-ionized acid HA remains . Examples of strong acids are hydrochloric acid (HCl), hydroiodic acid (HI), hydrobromic acid (HBr), perchloric acid (HClO), nitric acid (HNO) and sulfuric acid (H SO). In aqueous solution, each of these essentially ionizes about 100% </P> <P> In contrast, a weak acid only partially dissociates . Examples in water include carbonic acid (H CO) and acetic acid (CH COOH). At equilibrium, both the acid and the conjugate base are present in solution . </P> <P> Stronger acids have a larger acid dissociation constant (K) and a smaller logarithmic constant (pK = − log K) than weaker acids . The stronger an acid is, the more easily it loses a proton, H. Two key factors that contribute to the ease of deprotonation are the polarity of the H--A bond and the size of atom A, which determines the strength of the H--A bond . Acid strengths also depend on the stability of the conjugate base . </P> <P> While the pK value measures the tendency of an acidic solute to transfer a proton to a standard solvent (most commonly water and DMSO), the tendency of an acidic solvent to transfer a proton to a reference solute (most commonly a weak aniline base) is measured by its Hammett acidity function, the H value . Although these two concepts of acid strength often amount to the same general tendency of a substance to donate a proton, the pK and H values are measures of distinct properties and may occasionally diverge . For instance, hydrogen fluoride, whether dissolved in water (pK = 3.2) or DMSO (pK = 15), has pK values indicating that it undergoes incomplete dissociation in these solvents, making it a weak acid . However, as the rigorously dried, neat acidic medium, hydrogen fluoride has an H value of--15, making it a more strongly protonating medium than 100% sulfuric acid and thus, by definition, a superacid . (To prevent ambiguity, in the rest of this article, "strong acid" will, unless otherwise stated, refer to an acid that is strong as measured by its pK value (pK <--1.74). This usage is consistent with the common parlance of most practicing chemists .) </P>

Why hcl is weak acid in acetic acid