A 25.0-mL sample of 0.125 M pyridine is titrated with 0.100 M HCl. Calculate the pH at each volume of added acid: one-half equivalence.

Key Concepts

Titration

Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. It involves the gradual addition of a titrant (in this case, HCl) to a solution of the analyte (pyridine) until the reaction reaches its equivalence point. The volume of titrant used at this point allows for the calculation of the analyte's concentration.

Equivalence Point and Half-Equivalence Point

The equivalence point in a titration is reached when the amount of titrant added is stoichiometrically equivalent to the amount of analyte present. The half-equivalence point occurs when half of the analyte has reacted, which is significant for weak acid-strong base titrations as it allows for the calculation of pH using the Henderson-Hasselbalch equation, reflecting the balance between the weak base and its conjugate acid.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a formula used to calculate the pH of a buffer solution. It relates the pH to the pKa of the acid and the ratio of the concentrations of the conjugate base and the acid. In the context of the titration of pyridine with HCl, this equation is essential for determining the pH at the half-equivalence point, where the concentrations of pyridine and pyridinium ion are equal.