Question

A) Calculate the pH of a 0.0100 M solution of butylamine by making the assumption that the formal concentration is equal to the equilibrium molarity of the butylamine in solution.

B) Calculate the percent error incurred by "cutting corners" with the assumption in part A

C) Solve part A by using the technique of successive iterations.

D) Solve part A by using the quadratic

Answer 1

Butylamine is a base have K_b = 3.98 x 10-4. to calculate the initial pH of a weak base the reaction could be

                                         

Initial                                   0.01                               0                   0

Equilibrium                          0.01 - x                          x                   x

Final                                  0.01 - x                           x                   x

solving the quadratic equation using

x = [OH^-]=1.975 x 10^-2

pOH = - log x

pOH = - log 1.975 x 10^-2

pOH = 0.591

The pH can then be derived from the pOH using

pH = 14 - pOH

pH = 14 - 0.591

pH = 13.40