Knowledgebase

Background:

This experiment builds upon the skills the student developed in the Titration I lab. Each student is assigned a different weak acid to analyze for K_a and molecular weight. A measured mass of the solid weak acid is dissolved in water and titrated with a solution of NaOH with known concentration added drop-wise from the burette. The pH of the solution is continuously displayed on the monitor versus the mL of added titrant. After the endpoint volume is known, the student determines the pH at the point of maximum buffering and thus the pK_a of the weak acid. The volume at the endpoint is then used to calculate the molecular weight of the weak acid. Replicate titrations are performed. The student is asked to analyze the method and its limitations.

Learning Objectives:

1. Use an acid-base titration to analyze and unknown weak acid.
2. Learn how to use the pH of the point of maximum buffering on the titration curve to obtain the K_a value for the weak acid.
3. Be able to calculate the molecular weight of a weak acid from the mass dissolved and the volume of titrant required to reach the endpoint.
4. Be able to discuss the titration method and its limitations.