Question

On the polyprotic weak acid/strong base titration curve below, label the following points.

The point where the pH corresponds to a solution of H2A in water.

The point where the pH corresponds to a solution of HA- in water.

The point where the pH corresponds to a solution of A2- in water.

The point where pH = pKa1.

The point where pH = pKa2.

Answer 1

Concepts and reason

The value of titrations are recorded in the form of a graph and is represented as titration curve. The graph is plotted with respect to independent variable of volume and dependent value of pH. The titration curve will change according to the strength of an acid and a base.

Fundamentals

In the titration curve, the point where the base starts to neutralize the acid is represented as an equivalence point. Polyprotic acids on reaction with strong base results in more stages of neutralization. Because, the titration first occurred in the most acidic group rapidly, and then followed by the next most acidic group and so on

The point at which the concentration of an acid and a base is same is represented as midpoint. At this point, ${\rm{pH}}\,\,{\rm{ = }}\,\,{\rm{pKa}}$ .

Example: Graph of a polyprotic acid and a strong base. The midpoint and equivalence points are plotted in the graph.

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