You learned about macroscopic and microscopic p K a s when the mechanism of enol

Question

You learned about macroscopic and microscopic pKas when the mechanism of enolase was discussed during our chapter on carbohydrate metabolism. A dicarboxylic acid that can cause problems if ingested is called oxalic acid. Given that pK1 of oxalic acid is 1.27 and pK2 is 4.27, calculate the value of the microscopic ionization constant pKA. Hint: see the lecture slides that discussed enolase for definitions of the above species. Also, consider that oxalic acid/oxalate is a symmetrical molecule. Report your answers to the nearest hundredths of a unit.

And how would you go about solving for the other ionization constants pKB or pKC?

Explanation / Answer

pK1 = 1.27

pK2 = 4.27

R = Tautomeric ratio = 1 ( since oxalic acid / oxalate is a symmetrical molecule)

pKA = pK1 + log ( 1 + R) = 1.27 + log ( 1 + 1) = 1.57

pKB = pKA - log R = 1.57 - 0 = 1.57

pKC = pK2 - log ( 1 + R) = 4.27 - 0.30 = 3.97

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