Predict whether the equivalence point of each of the following titrations is below, above, or at pH 7: (c) pyridine titrated with nitric acid.

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Identify the nature of the substances involved in the titration: Pyridine is a weak base, and nitric acid is a strong acid.

Understand the reaction: When a weak base is titrated with a strong acid, the resulting solution at the equivalence point will contain the conjugate acid of the weak base.

Consider the properties of the conjugate acid: The conjugate acid of pyridine is pyridinium ion, which can donate a proton to water, making the solution acidic.

Predict the pH at the equivalence point: Since the solution contains an acidic species (pyridinium ion), the pH at the equivalence point will be below 7.

Conclude: The equivalence point of the titration of pyridine with nitric acid is below pH 7.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acid-Base Titration

An acid-base titration is a quantitative analytical method used to determine the concentration of an acid or base in a solution. During the titration, a solution of known concentration (the titrant) is added to a solution of unknown concentration until the reaction reaches the equivalence point, where the amount of acid equals the amount of base. The pH at this point can vary depending on the strength of the acid and base involved.

Strength of Acids and Bases

Acids and bases are classified as strong or weak based on their ability to dissociate in water. Strong acids, like nitric acid, completely dissociate into ions, while weak bases, such as pyridine, only partially dissociate. This difference in dissociation affects the pH at the equivalence point of a titration, with strong acids and weak bases typically resulting in a pH below 7 at the equivalence point due to the presence of excess hydrogen ions.

Equivalence Point and pH

The equivalence point in a titration is the stage at which the amount of titrant added is stoichiometrically equivalent to the amount of substance in the sample. The pH at this point is influenced by the nature of the acid and base involved. In the case of titrating a weak base with a strong acid, the resulting solution will have a pH less than 7 due to the formation of a conjugate acid, which contributes to the acidity of the solution.

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Assume that 30.0 mL of a 0.10 M solution of a weak base B that accepts one proton is titrated with a 0.10 M solution of the monoprotic strong acid HA. (a) How many moles of HA have been added at the equivalence point?

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Assume that 30.0 mL of a 0.10 M solution of a weak base B that accepts one proton is titrated with a 0.10 M solution of the monoprotic strong acid HA. (c) Is the pH 7, less than 7, or more than 7 at the equivalence point?