3.2: Titration of a Strong Acid with a Strong Base

During the titration of a strong acid with a strong base, pH calculations are primarily based on the concentration of residual hydronium or hydroxide ions. Initially, a strong acid like hydrochloric acid fully dissociates, creating hydronium and chloride ions, resulting in a low pH. The addition of a strong base like sodium hydroxide alters the concentration of hydronium ions by neutralizing them. As more base is added, the pH gradually increases. At the equivalence point, all hydronium ions are neutralized, achieving a neutral pH. Beyond this point, the excess hydroxide ions dictate the pH, making the solution basic. The new pH can be calculated by considering the concentration of these excess hydroxide ions.

During the titration of a strong acid with a strong base, the pH calculations are based on the concentration of the residual H₃O⁺ or OH⁻ ions.

For instance, 0.1 M HCl dissociates into 0.1 M H₃O⁺ and Cl⁻ ions, starting with an initial pH of approximately 1.

The introduction of 0.1 M NaOH alters the H₃O⁺ concentration in the solution. The new concentration can be calculated by subtracting the total moles of OH⁻ from those of H₃O⁺ and dividing by the total volume. Now, the resultant pH has risen to 1.48.

The continued addition of NaOH solution neutralizes all the H₃O⁺, raising the pH to 7 at the equivalence point.

Beyond this point, OH⁻ govern and determine the pH.

Adding more NaOH solution containing 0.007 moles of OH⁻ results in a final OH⁻ concentration of 0.017 M with the corresponding pOH of 1.77 and pH of 12.23.