Final answer:
In acid-base equilibria in aqueous solutions, water acts as both an acid and a base. Water molecules can donate and accept protons, forming hydroxide and hydronium ions, respectively. The reaction between these ions neutralizes each other, forming water, and reflects the acid or base strength in relation to water and hydroxide ion.
Step-by-step explanation:
The reason water (H₂O) is used to deprotonate the oxonium ion (H₃O+) rather than a hydroxide ion (OH⁻) in certain acid-base reactions is primarily due to the nature of acid-base equilibria in aqueous solutions. In these reactions, water acts as both an acid and a base - a concept known as autoionization.
In a reaction involving base ionization, the hydroxide ion produced can further react with hydronium ion in the solution, leading to the formation of two water molecules according to the reaction H₃O+ (aq) + OH⁻ (aq) = 2H₂O(l). This reaction has a 1:1 stoichiometry, indicating that an added hydroxide ion would simply neutralize an existing hydronium ion, thus not changing the overall acidity or basicity of the solution unless an excess of hydroxide is added.