Weak Acid Lab

The purpose of the K_a determination of an unknown weak acid lab was to use titration in order to determine the K_a for an unknown solid weak acid knowing only its molar mass. The previous laboratory experiment was performed in order to determine whether titration or dilution would yield more accurate K_a. It was determined that titration yielded more accurate results. This lab was performed by taking a sample of solid weak acid and dissolving it in water before titrating with the strong base NaOH. Titration is a technique in which a reagent of known concentration is slowly added to an unknown solution in order to calculate the concentration of the unknown. When a weak acid is titrated with enough of a strong base, the weak acid is converted into its

The volumetric flask was then filled up to its 100 mL mark with deionized water. The buret was washed out with dionized water and then with the strong base NaOH before being filled up with NaOH. About 20 mL of the unknown weak acid was pipetted into a beaker. The starting volume of the NaOH in the buret was recorded before about 4 mL of the strong base was titrated into the weak acid solution. The final volume was recorded. A pH probe connected through Microlab was calibrated using buffer solutions of pH 4.00, 7.00, and 10.00. The calibrated pH probe was used in order to measure the pH of the titrated solution of the unknown weak acid. These same steps were repeated except 2 mL of the strong base were titrated into the weak acid solution instead of 4 mL. This process was repeated 10 times.

Data

The data from Table 1 was gathered by calculating the pK_a and K_a of the unknown weak acid using the change in volume and pH of the solution. The table contains data for trial number, starting and final volume, change in volume, pH of the solution, pK_a of the solution, and K_a of the