Potentiometeric Titrations

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.

Methods:

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 ...

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... data due to students not finishing their titration in time. However it can be said by looking at the data that acetic acid is not as strong as HCl. The initial pH and the half equivalence points for the acetic acid is higher then HCl, making it a weak acid. Acetic acid also uses more of the base to reach its equivalence point. For formic acid, it can be said by looking at the data that formic acid is a little stronger weak acid then acetic acid. That is because initial pH and the half equivalence points

of formic acid are smaller then acetic acid. For formic acid, the data also shows that as the concentration of the acid gets higher, more volume of the base is needed to reach the equivalence point. For acetic acid and formic acid, it should be noted that their pH higher then HCl. That is because the weak acids reacting with a strong base reach a pH higher then 7.