Calculation of Molecular Benzoic Acid Questions


    1. The pKa of benzoic acid is 4.20. Please calculate how much percent of benzoic acid is in the molecular form in pH 3.50 buffer solution.
    2. If the pH of the buffer solution is 10.0, which one one, ascorbic acid or caffeine or benzoic acid, will have the longest retention time in a nonpolar column? Why?
    3. In a reversed phase HPLC experiment, a mixture of an aqueous buffer and methanol is used as the mobile phase. When run an unknown on the HPLC using 50:50 buffer and methanol mobile phase, one can find two peaks in the chromatogram, in which the retention time for the first peak is 96 seconds, however, the retention time for the second peak is 560 seconds. If one wants the second peak comes out more quickly, more methanol or less methanol should be added into the mobile phase? explain
    4. In this experiment, one standard is used to determine the concentration of the unknown. If one wants to use a calibration curve to determine the unknown, how to accomplish it? please describe the main procedures in such an experiment, and how to treat the data
    5. As directed in the lab manual, a student is preparing the standard solution, after pipetting 1000 µL into the 10.00 mL volumetric flask, he then uses his buffer solution to dilute his sample. He accidentally goes over the dilution mark on the volumetric flask and chooses to ignore his error. When comparing the unknown to this over diluted sample, would you expect the unknown concentration to be higher or lower?
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