Determination of the Acid Ionization Constant PDF

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Determination of the Acid Ionization Constant, Ka

Purpose The purpose of this experiment is to determine the pKa of a weak monoprotic acid. Procedure Given in Course Material File Data Tables None Calculations  ½ way point pH = pKa 

pKa = -log (Ka)

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Ka = 10 ^(-pH)

1. pH = pKa = 4.63 2. Ka= 10(-4.63) 3. Ka = 2.344 x 10 - 5 Summary of Results 

Equivalence Point Volume: 21.50 mL

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Half Equivalence Point Volume: 10.75 mL

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pKa: 4.63

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Ka: 2.344 x 10 – 5

Conclusion The purpose of this lab was to determine the pKa of a weak monoprotic acid, and this was accomplished by the calculations shown above. The equivalence point was found by determining where the volume that corresponds to the highest peak in the plot was for the first derivative plot, which was 21.50 mL. The half equivalence point volume was determined by diving the equivalence point volume in half with a value of 0.75 mL. The pH is equal to the pKa at half the equivalence volume, this was determined to be 4.63. The ka value was calculated by raising 10 to the -4.63 power, concluding a Ka value of 2.344 x 10 – 5. Errors that may have occurred in this lab is if the volume was not recorded correctly from the buret. Another error that may have occurred

while conducting this experiment is if is calibration of the pH electrode was not done properly. If calibration is off then pH is offset high or low....