Explain why the differences between the first and second pKa values of the dicarboxylic acids become smaller as the lengths of their carbon chains increase (Table 20.3).

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TABLE 20.3 pK, Values of Some Dicarboxylic Acids Acid* carbonic oxalic malonic succinic glutaric adipic phthalic First pK 1.27 2.86 4.21 4.34 4.41 2.95 Second pk. 10.33 4.27 5.70 5.64 5.27 5.28 5.41 See Table 20.1 for structures "This value, which corrects for the amount of H2CO, in aqueous CO2, is the actual pK, of carbonic acid, An often-cited value of 6.4 treats all dis- solved CO, as H,CO,