The hydronium ion always forms when an acid dissolves in water. The H+ from the acid always goes to the nearest water molecule and forms H3O+. Another way to look at the hydronium ion is to take the point of view of the proton (H+). Adding water to something is called hydration.

What is a hydronium ion and how and why is it formed?

=>> Hydronium ion is a water molecule with an extra hydrogen ion attached to it. ( H2O + H+→ H3O+). It usually used to determine the acidity of a chemical compound. ... It is formed by the combination of hydrogen ion H+ given by an acid and water molecule.

What produces hydronium ion?

A strong acid reacts completely with water to produce hydronium ions. A weak acid reacts incompletely with water to produce hydronium ions.