Problem 15-57

Consider CH₃NH₃Cl as a weak acid (with Cl^- a spectator ion):

CH₃NH₃⁺     CH₃NH₂   +   H⁺

a. complete neutralization: not a buffer
b. mixture of two bases: not a buffer
c. Complete neutralization of the acid and KOH in excess: not a buffer
d. You have a reaction between a weak acid and a strong base (strong base = complete reaction, all consumed).
After the reaction, you have a buffer since there is a considerable
amount of both the conjugate acid/base system present in the solution.