Sulfuric Acid and Water: Paradoxes of Dilution

The principal goal of this article is to elucidate some uncommon phenomena that can be observed in the process of diluting sulfuric acid with water. The thermochemistry and equilibrium properties of aqueous solutions of sulfuric acid are described. It is shown that even in very dilute solutions, dissociation of sulfuric acid proceeds completely only for the first equilibrium. The article contains interesting information about thermochemical measurements carried out in the 19th century and a discussion concerning the heats of hydratation. It also describes the possibility of obtaining unexpected results from the experimental data presented in the literature on the subject. Supplemental Material contains questions for students with answers and possible solutions. The questions and the discussions will be useful in general, inorganic, and physical chemistry courses.