On the weak base/strong acid titration curve, label A the point where the pH corresponds t0 4 solution of the weak base (B) in water; B the point where the pH corresponds to a solution of the conjugate acid (BHt) in water; Cthe point where pH = pKa for BH+ , Ansuer Bank 1 mL of titrant
The Correct Answer and Explanation is:
In a titration curve for a weak base (B) with a strong acid (HCl), the following points can be labeled:
Point A: This is the starting point of the titration curve, which corresponds to the pH of the weak base (B) in water, before any titrant has been added. When a weak base is dissolved in water, it undergoes partial dissociation to produce hydroxide ions (OH⁻) and its conjugate acid (BH⁺). Since the base is weak, it does not dissociate fully, resulting in a relatively basic pH, typically around 9-11, depending on the strength of the base. In this context, Point A refers to the pH of the weak base solution (B).
Point B: This is the point where enough titrant (strong acid, HCl) has been added to neutralize the weak base (B). At this point, the solution consists predominantly of the conjugate acid (BH⁺) and water. The pH here is determined by the hydrolysis of the conjugate acid (BH⁺), which releases protons into the solution, making it acidic. The pH at Point B is typically lower than that at Point A, and it’s often around 5-6, depending on the concentration of the conjugate acid.
Point C: This point corresponds to the pH at which the solution contains equal concentrations of the conjugate acid (BH⁺) and its base form (B). It is the half-equivalence point in the titration curve and represents the point where the pH equals the pKa of the conjugate acid (BH⁺). At this stage, the concentrations of BH⁺ and B are equal, so the pH is equal to the pKa of the conjugate acid, which is typically around 5-7 for most weak bases.
Answer Bank for 1 mL of titrant: The exact volume of titrant needed to reach these points depends on the concentrations of the weak base and the titrant. At Point A, you would expect the pH to be around 9-11 for a weak base in solution. At Point B, the pH will be acidic, typically around 5-6, and at Point C, the pH equals the pKa, which is around 5-7.
