Final answer:
The hydrogen ion is often written as H+, which is a simplified notation used in acid-base chemistry, although in aqueous solutions it exists as the hydronium ion, H3O+.
Step-by-step explanation:
The formula of the hydrogen ion is often written as H+. In the context of aqueous solutions, this notation is a simplification used to represent acid-base reactions where the exact proton donor-acceptor mechanism is not emphasized. In reality, a hydrogen ion in water is more accurately represented as the hydronium ion, H3O+, because hydrogen ions are always associated with water molecules in solution. Nevertheless, it is common to use the H+ notation for convenience, especially when balancing chemical equations or discussing acids and their ionization in water, as seen in the Henderson-Hasselbalch approximation and equation.