What type of acids does the Arrhenius theory define?

• A. Acids that form OH- in water
• B. Acids that form H2O in water
• C. Acids that form H3O+ in water
• D. Acids that form H+ in air

Answer: (C)

The Arrhenius theory defines acids as substances that, when dissolved in water, increase the concentration of hydronium ions (H3O+). This definition stems from the premise that acids are proton donors. When an acid dissolves in water, it releases protons (H+), which then associate with water molecules to form hydronium ions. Thus, the presence of H3O+ in the solution characterizes an Arrhenius acid, reflecting the typical behavior of acids in aqueous solutions.

In contrast, while the formation of hydroxide ions (OH-) is relevant to bases within the Arrhenius framework, it does not pertain to the definition of acids. Similarly, the generation of water (H2O) or the formation of hydrogen ions (H+) in air is not central to the Arrhenius acid concept. The focus remains on the generation of hydronium ions in water, making the correct answer the one that refers to acids creating H3O+ in a dilute aqueous context.