work check and help with the last question. pka2 is more accurate than pka1. 58

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work check and help with the last question. pka2 is more accurate than pka1.

58 5. Calculation of molar mass: Use class-average NaOH molarity and your part B data. (Be sure this calculation is consistent with your choice reported in #1 and 2 above.) 6. Complete the following table, having consulted a table of diprotic acids; taking into account molar mass and pKa's, identify your unknown: I Molar mass pKa1 pKa2 From titration data Data from reference | 6-1 Unknown: Maleic acid t.33 7. "It is possible to show" the first equivalence point pH of a diprotic acid is equal to the average of the two pKa values. Calculate the average of the pKa values for your unknown: .16 Use your graph to determine the pH at the first equivalence point: How much of a difference is there? 8. You produced two buffer regions in the diprotic acid titration. What two pH ranges would your system be best suited for as a buffer? (Where is pH most stable? Refer to your graph.) PH 0 2,and PH 0 5 -6 9. If you had not been told that your unknown was a triprotic acid, and it actually was, how would your results for pKal, pKa2, and your molecular weight calculation be different?

Explanation / Answer

I have checked your work. Well done! Keep going ahead.

Now, coming to the last question:

The pKa1 and pKa2 values will be obtained more than the actual or expected values for a triprotic acid. As a result, the molecular weight will be less than the actual one.

Explanation: For a triprotic acid: pKa1 < pKa2 < pKa3

But here, if you don't know that you are using triprotic acid, you will treat it like a diprotic acid and you will get pKa1 and pKa2 values for diprotic acid type, whose values are more than those for the triprotic acid.

Now, Ka is inversely related to [acid]

pKa is inversely related to Ka.

Therefore, pKa is directly related to [acid], moles of acid.

As a result of an increase in no. of moles of acid, its molecular weight decreases.

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