When doing an ICF chart or a ICE chart. How do I know my initial Base or Acid concentration does not need to be changed for the final amount?

When doing an ICF chart or a ICE chart. How do I know my initial Base or Acid concentration does not need to be changed for the final amount? For example:

1.     (C2H5)3N + H2O -> (C2H5)3NH+ + OH-

I .0304M                    0                  0

C -x                              +x                +x

E .0304-x                      x                 x

 Kb = x2/.0304-x

5.2x10-4 = x2/.0304-x

0 = x2 + 5.2x10-4x - .0000158

X= 5.2x10-4 +/- ((5.2x10-4)^2-(4*1*-.0000158))^(1/2)/2

X = -.00424, .0037M You can remove the negative answer.

Therefore [OH-] = [(C2H5)3NH+] = .0037

[(C2H5)3N] = .0304-.0037 = .0267M

pOH = -log [OH-] = -log(.0037) = 2.43

pH = 14-2.43 = 11.57

%dissociation = .0037/.0304 x100% = 12

And # 2

    C5H5N +H2O -> C5H5NH+ + OH-

I .0143M                 0            0

C -x                          +x          +x

E .0143-x                  x           x

Kb = x2/.0143-x

1.7x10-9 = x2/.0143-x

0 = x2+1.7x10-9x-2.431 x10-11

X= -1.7x10-9 +/- ((1.7x10-9)2 - 4(1)(- 2.431 x10-11))1/2/2

X = 4.93 x10-6 and - 4.93 x10-6. You can remove -4.93 x10-6 because a negative answer makes no sense.

Therefore [C5H5NH+] = [OH-] = 4.9 x10-6

[C5H5N] doesn't change so it is still .0143M

The pOH is easier to find pOH = -log(4.9 x10-6) = 5.31

pH = 14-pOH = 14-5.31 = 8.69

Why does C5H5N in #2 not change and (C2H5)3N does change for finding the concentrations?