When classifying acids or bases, what is the primary factor being assessed?

The primary factor in classifying acids or bases is their ability to ionize in solution. This concept is fundamental to the definitions of acids and bases according to the Brønsted-Lowry and Arrhenius theories. An acid is characterized by its ability to donate protons (H⁺ ions) in solution, whereas a base is defined by its ability to accept protons or produce hydroxide ions (OH⁻) in solution.

When an acid or base is dissolved in water, the extent to which it dissociates into its constituent ions determines its strength. Strong acids and bases ionize completely, leading to a high concentration of ions, while weak acids and bases only partially ionize, resulting in fewer ions in solution. This ionization process directly impacts the properties of the solution, such as pH and conductivity, making it a crucial factor for classification.

In contrast, molecular weight, boiling point, and color in solution do not directly relate to the acid-base behavior of a substance in aqueous solutions. These properties may vary widely among different acids and bases but do not influence the classification based on acid-base theory. Thus, the ability to ionize is indeed the central criterion for categorizing acids and bases effectively.