Experiment 21 Acid Base Titration Curves Determining pKa Chemistry 1220 136 October 21st 2013 Raffeal Bennett Purpose The purpose of this experiment was to follow a titration progession using a pH meter and recording changed values Also to use titration data to plot the curve to extract the pH at the equivalence point Furthermore the experiment taught to utilize the Henderson Hasselbach equation to determine the pKa of the acid Procedure Refer to pages 86 88 of General Chemistry 1220 Laboratory Manual by The Ohio State University Department of Chemistry Hayden McNeil Publishing 2013 2014 Sample Calculations See attached sheet Graph See attached sheet with graph Discussion Based on the information learned in the lecture the titration curve looks as expected for this particular Acid Base titration As the base kept being added there was not a large change in pH initially because of the buffer region but as more was added there was a sharp increase in pH The middle of this steep rising portion of the titration curve is the equivalence point The molarity of the acid in the unknown was found to be 0 0728 M The pKa value at equivalence is 3 68 at 3 70 and at 3 72 The Henderson Hasselbach equation relates the pH to the pKa and at 1 2 equivalence point the pH will equal the pKa For and the log 1 3 and log 3 was added respectively 0 477 giving similar pKa values at all point The values agree within 0 20 of each other Since the same acid was used throughout the experiment the pKa will not changed in the same titration Sources of error in this experiment that should be considered are the accuracy of estimates of values from the graphs accuracy of measurement and accuracy of titration When estimating from the graph the values cannot be certain due to personal perspective Also the measuring devices used were only clear to a certain value which could also lead to problems in measuring Moreover the pH values on the meter jumped around as time passed which is a clear source of error since it was not the same consistent number Conclusion In part A of the experiment the pH meter was standardized In part B the unknown acid was titrated 2 different times the first one using 0 50 mL increments while the second titration the volume of NaOH added was based off the first titration making the pH rise in the end Around the estimated equivalence point the 1 drop additions of NaOH were used to give four points to the graph The molarity of HA was found to be 0 0728 M then the pKa values were found for being respectively 3 68 3 70 and 3 72 Throughout the experiment the pH changes were noted so that the equivalence point would be found