Final answer:
A strong acid is characterized by its complete ionization in aqueous solution, releasing all its hydrogen ions to form a stable conjugate base. The strength of an acid is indicated by a low pKa value.
Step-by-step explanation:
Characteristics of a Strong Acid
The characteristic that defines a strong acid is its ability to completely ionize in an aqueous solution. When we say an acid is strong, we are saying that it donates its hydrogen ions (H+) readily into the solution. This results in the formation of a stable conjugate base. A common example of a strong acid is hydrochloric acid (HCl), which dissociates completely into hydrogen and chloride ions in water. In contrast, weak acids such as acetic acid found in vinegar ionize only slightly, resulting in an equilibrium where a significant amount of the acid remains undissociated.
The ionization of a strong acid in solution is represented by the reaction:
HC1 (g) → H+ (aq) + Cl¯ (aq)
The strength of an acid is quantified by its acid ionization constant (Ka) or by its pKa value. The smaller the pKa, the stronger the acid. For strong acids, this value is very low, indicating a high degree of ionization in solution.