pH in the Absence of a Buffer

If we add a strong acid or strong base to water, the pH will change dramatically. For instance, adding a strong acid such as HCl to water results in the reaction HCl + H₂O → H₃O⁺ + Cl^-. In other words, the proton (H⁺) from the acid binds to neutral water molecules to form H₃O⁺ raising the concentration of H⁺. The resulting large concentration of (H⁺) makes the solution more acidic and leads to a dramatic drop in the pH.

Solid NaOH consists of Na⁺ and OH^- ions packed into a crystalline lattice. When this solid is added to water, the ions float apart leading to extra OH^- ions in the water: NaOH → OH^- + Na⁺. The resulting large concentration of OH^- makes the solution more basic and leads to a dramatic increase in the pH. (Remember that since the product of concentrations, [OH^-][H⁺], remains fixed at K_w=10^-14, as the concentration of OH^- ions goes up, the concentration of H⁺ ions goes down.)