Experiment # 4: Dissociation Constant Weak Acids
Introduction: The dissociation constants of weak monoprotic acids were determined with the aid of a buffer and pH meter.
Experiment: This experiment was performed according to the procedures as provided in the Chemistry 111B laboratory manual: Po, Henry and Senozan, N. "General Chemistry Experiments Chemistry 111B", 8th Ed., 2004 Hayden-McNeil Publishing, pp 80-88. To determine the dissociation constants of weak monoprotic acids (HX and HY), a buffer was needed to calibrate the pH meter. According to the manual, all four solutions to the experiments had to be carried out first before the calibration was performed. The following materials were obtained to conduct the parts of the experiment: 1) several 10-mL and 50-mL graduated cylinders to measure the volumes of acid and base, and 2) a thermometer to record the temperature of the solution.
In the first half of the experiment, the Ka of HX had to be used and determined and in the second half, the Ka of HY was utilized and established using the same procedure.
In the first part of the experiment, the pH and temperature was to be measured of a 10 mL sample of 1.02 M HA (when conducting the second half of the experiment, the concentration of HY was 1.00 M). The second part of the experiment was to add 20 mL of 1.0 M NaA to 10 mL of 1.00 M HA, and to draw 10 to 15 mL of the solution to measure the pH and temperature. For the third part of the experiment, 10 mL of the
remaining buffer from part 2 was diluted with 50 mL of distilled water. The pH and temperature was measured for this part of the experiment. The last part of the experiment was to mix 10...