Final answer:
When an acid like HCl dissolves in water according to the Arrhenius theory, it produces hydrogen ions (H+), which then combine with water to form hydronium ions (H3O+).
Step-by-step explanation:
According to the Arrhenius theory, when an acid dissolves in water, it produces hydrogen ions (H+), which immediately combine with water molecules to form hydronium ions (H3O+). This is represented by the chemical equation where hydrochloric acid (HCl) in aqueous solution dissociates completely into hydrogen ions and chloride ions:
HCl(aq) + H2O(l) → H3O+(aq) + Cl−(aq)
The hydrogen atom, consisting of a single proton and electron, when in solution as an H+ ion, does not exist freely but attaches to a water molecule forming the hydronium ion. Both H+ and H3O+ represent the acidic species, but using H3O+ indicates the absence of bare protons in solution.