A 0.100 solution of ethylamine () has a of 11.87. Calculate the for ethylamine

 

So I took the pH and calculated that x = 7.4 x 10^-3 M

 

THen I set up one of those ICE charts:

                       + H20  -->   C2H5NH3+  + OH-

Initial               0.100                              ----                  ----

Change             -x M                             + x M                 + x M

EQuil. Concen  0.100 - x M                      x M                  x  M

 

Then I used Kb =  x^2 divided by (0.100- x)

 

My answer was 5.9 x 10^-3 but that is not the right answer.  I don't know where I went wrong