Sulfuric acid is unique in being a strong acid in its first dissociation step and a weak acid in its second step. For rela- solutions of sulfuric acid (1.0 M or higher). tively concentrated the large concentration of H from the first dissociation step represses the second step, which can be neglected as a contrib- utor of H ions. For dilute solutions of sulfuric acid the second step does make a significant contribution, and must be considered in obtaining the total H concentration.