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The first entry in PubChem for the $\mathrm pK_\mathrm a$ of methylamine is $10.657$ at $25\ \mathrm{^\circ C}$. My elementary understanding is that this would be found as the negative log of the $K_\mathrm a,$ but the $K_\mathrm a$ is given as $2.70\times10^{-11}$ for which the negative log is about $10.568$.

My guess was that the two are determined independently, but can anyone shed some light on the seeming discrepancy?

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  • $\begingroup$ A discrepancy of 0.1 in pKa is as good as no discrepancy at all. $\endgroup$ – Ivan Neretin Oct 5 '18 at 11:34
  • $\begingroup$ @IvanNeretin: Oh. They are each found experimentally...? $\endgroup$ – daniel Oct 5 '18 at 11:55
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    $\begingroup$ Maybe.$\mathstrut$ $\endgroup$ – Ivan Neretin Oct 5 '18 at 11:57
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    $\begingroup$ Humans create all that data. I'd guess that the 5 and 6 got transposed. $\endgroup$ – MaxW Oct 5 '18 at 13:30

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