Title: Potentiometric Titration
Purpose: The purpose of this lab was to construct a titration curve by titrating Formic acid using a standardized sodium hydroxide (NaOH) and a pH meter through potentiometric titration. After the data for the rest of the class is collected, compare and contrast the equivalence points to see how the concentrations of the various acids affected the acids weakness and strength.
Obtain 0.020 M of Formic Acid (HCCOOH). Calibrate the pH meter using the instructions for calibrating the pH meter in the appendix. After the calibration of the pH meter, 150 mL of Formic acid solution was dispensed into a clean dry beaker, and then 50 mL of the formic acid was transferred into a 250mL beaker. After the burette was rinsed twice with a couple of mL of standardized (NaOH) solution, it was filled with approximately 0.62 mL (NaOH)(start anywhere between 0.1 to 1ml). The pH meter was put into the beaker of acid, and a "rough" titration was performed by adding (NaOH) about 1 mL at a time from the burette into the beaker. At this point record the volume added and pH at each 1 ml interval. Since our initial reading of the burette was 0.62 mL with a pH of 2.31, a subtraction of our initial reading from each of our burette readings is needed in order to obtain more accurate readings.
The titration was continued until a jump occurred between the pH indicating that an equivalence point had been reached somewhere between the jump. Next a more accurate titration was performed, meaning recording more data points around the equivalence point by adding smaller amounts of base. The pH meter was calibrated again, and 50 mL of Formic Acid was dispensed into a 250 mL beaker. The pH meter was placed in the beaker, and we started with 0.20 mL of (NaOH) of pH 2.57. This time we added smaller and smaller amounts of base into the beaker until we reached a total volume with in 2 mL of our equivalence point. The size of (NaOH) was reduced to about 0.1 mL per intervals. A titration curve was made for 0.20 M of Formic Acid and results were shared in class. After the data has been collected from the rest of the class, compare and contrast the properties of various acids titrated with a strong base. Keep in mind that that the pH of the strong acid reacted with strong base will give a pH of about 7 and a weak acid with a strong base will give a pH higher then 7.
Table 1: Acids Studied in the Experiment
Acid Ka1 Ka2
Hydrochloric acid, HCl very large N/A
Acetic acid, CH3COOH 1.76E-5 N/A
Formic acid, HCOOH 1.77E-4 N/A
Maleic acid, HOOCCHCHCOOH 1.42E-2 8.57E-7
Acids with very large Ka values are very strong acids. Acids with very small Ka are very weak acids. Hydrochloric acid is very strong because of its very large ka value, and the rest of the acids are weak because of their small Ka values. Hydrochloric acid, acetic acid, and formic acid are all monoprotic. Maleic acid is diprotic because it has...