Beyond equivalence, the pH is mainly determined by:

Beyond equivalence, the pH is mainly determined by:

• A. The amount of HA remaining.
• B. The hydrolysis of A- producing OH-.
• C. The strength of water autoprotolysis.
• D. The color of the solution.

Answer: (B)

After the equivalence point, the solution mainly contains the conjugate base A-. This species reacts with water in a hydrolysis process: A- + H2O ⇌ HA + OH-. The amount of OH- produced by this hydrolysis determines the pH, making the solution basic. This relationship is governed by the base hydrolysis constant Kb (Kb = Kw/Ka). So the pH is set by how readily A- hydrolyzes in water, not by the amount of HA remaining, water's autoprotolysis alone, or the solution’s color. (Excess strong base would eventually dominate if added in large amounts, but immediately beyond equivalence the hydrolysis of A- is the main factor.)

After the equivalence point, the solution mainly contains the conjugate base A-. This species reacts with water in a hydrolysis process: A- + H2O ⇌ HA + OH-. The amount of OH- produced by this hydrolysis determines the pH, making the solution basic. This relationship is governed by the base hydrolysis constant Kb (Kb = Kw/Ka). So the pH is set by how readily A- hydrolyzes in water, not by the amount of HA remaining, water's autoprotolysis alone, or the solution’s color. (Excess strong base would eventually dominate if added in large amounts, but immediately beyond equivalence the hydrolysis of A- is the main factor.)