chem problem please help?

Question

Which of the following solutions result in a buffer ?



a) 0.050 L of 0.250 M NH3 + 0.100 L of 0.250 M HCl


b) 0.100 L of 0.250 M NH4Cl + 0.050 L of 0.025 M HCl


c) 0.100 L of 0.250 M NH4Cl + 0.050 L of 0.250 M NaOH


d) 0.100 L of 0.250 M NH4Cl + 0.150 L of 0.250 M NaOH

Answer 1

Did you all get the same homework or something?

c gives you a buffer, the others do not. To get a buffer, you need to have sufficient quantities of a weak acid and its conjugate base. After you've added the base to the weak acid solution in c, you have an incomplete reaction, which means that there will be some ammonium in solution as well as some ammonia. None of the other cases will give you that (in a, the reaction goes to completion, in b there is no reaction, and in d the reaction goes to completion).