The pH=8.60 for a 0.016 molar NTD (toluidine) solution. Find Kb of NTD.

Question

Answer is 1.0 * 10^-9 
I did the following calculations and ended up with something entirely different from what the answer is.

pH = 8.60
pOH = 5.40
pOH = -log[OH-]
[OH-] = 10^-pOH
[OH] = 3.98 * 10^-6

I then tried to do an ICE table
                C7H9N +H2O <-------->C7H10N + OH-
I.               0.016.                               0.           0
C.               -3.98*10^-6.                  +3.98*10^-6 +3.98*10^-6
E               0.016.                          3.98*10^-6.     3.98*10^-6

(3.98*10^-6)^2/0.016
9.9*10^-10
What did I do wrong?

DrBob222 · Answer

I don't think you did anything wrong. 9.9E-10 rounded is 10E-10 = 1E-9 fpr Kb. I looked up with a hugh amout of work (did you know Kb is listed for p-toluidine) ANYWHERE AND NO TABLES HAVE IT). Anyway, I finally found it on a label from a can. It was listed as pKa = 5.1 which makes Kb = 1.26E-9. Knowing that the Ka and Kb values, especially for those it took two hours to find on the web, probably are no better than 10 or 15%. Sorry this reply took so long but information on the web is so scare. By the way, there are literally at least six or seven problems with these exact numbers worked in full on the web and all of them come up with 9.9E-10.