Pka1 and pka2 for maleic acid

Titration of a Polyprotic Acid Post Lab

Calculations

Perform the following calculations. You must show your work for these. Word’s equation editor will let you

do this. You can’t write your work on a piece of paper, take a picture of the paper, and insert the picture.

1. Use your data to construct a plot of pH vs mL base added. Paste your plot into the document you

submit. Your plot must have appropriate labels for its axes.

2. Copy and paste all the columns you used to make your graph; that is, the “volume added,” “pH,” and

“Burette Reading” columns.

3. Determine the pKa(s) and the Ka(s) of the acid you worked with.

 This will require you to determine your titration’s equivalence and half-equivalence point(s),

including the solution pH these were reached at.

4. The actual pKa1 and pKa2 values of Maleic acid are 1.83 and 6.07 respectively. Calculate the percent

difference between these numbers and the pKa1 and pKa2 values you determined from your data. To

do this, subtract the smaller number from the larger and divide by the provided/literature values.

Results and Discussion

1. Write a brief summary of your experiment. As part of this, you have to describe:

a) What you were trying to accomplish

b) What your experimental approach was (or how you did it)

c) What your results were. Include the pKa and Ka values you calculated as part of your summary.

2. Comment on what the size of the difference between the acid’s actual and calculated pKa values tells

you about the accuracy of your pKa assay.

3. What factors, either experimenter or experimental, could have caused your calculated Ka/pKa values

to be too high or too low? What could have been done to avoid these errors?

4. Your titration graph can be divided into ten segments that are listed below. Discuss what the relative

(not numerical) concentrations of H2A, HA–, and A2– are in each of these ten segments. For example,

for segment “Q” you might say “in segment Q, there is a lot more A2– than HA– and almost no H2A in

solution” or maybe “the amounts of A2– and HA– are roughly equal and there’s just a little H2A.”

1. The start of the titration (no NaOH has been added.)

2. Between the first addition of NaOH to just before the 1st half-equivalence point

3. At the 1st half-equivalence point

4. Between the 1st half-equivalence point and the 1st equivalence point

5. At the 1st equivalence point

6. Between the 1st equivalence point and the 2nd half-equivalence point.

7. At the 2nd half-equivalence point

8. Between the 2nd half-equivalence point and the 2nd equivalence point

9. At the 2nd equivalence point

10. After the 2nd equivalence point