A hydronium ion is a positively charged ion formed by the reaction between a water molecule (H2O) and a hydrogen ion (H+). This reaction results in the formation of the chemical formula H3O+.
The chemical equation for this reaction can be written as follows:
H2O + H+ → H3O+
In an aqueous solution, the concentration of hydronium ions determines the pH (Potential of Hydrogen) of the solution. If hydronium ions are higher in a solution, their pH will be lower, and the solution will be more acidic.