Ionization of Acid in Aqueous Solution

When an acid is mixed with pure water, it dissociates and donates protons ($H^+$). Protons cannot exist independently in water and immediately combine with water molecules to form hydronium ions ($H_3O^+$): $HA + H_2O \longrightarrow H_3O^+ + A^-$

Formation of hydronium ions ($H_3O^+$)

Impact on Concentration

Mixing acid into water increases the total count and concentration of hydronium ($H_3O^+$) ions per unit volume in the solution compared to neutral water ($10^{-7}\text{ M}$).

Increases the concentration of hydronium ions per unit volume