Which of the following solutions result in a buffer ?

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

Only c does, a, b, and d do not.

a) Reaction of a strong acid with a weak base. Unfortunately, you have too much strong acid, so all of the base will be converted to its conjugate acid. You need sufficient quantities of both weak base and its conjugate acid to have a buffer.
b) Strong acid with a weak acid. There's actually no reaction here, so you can't form any of the conjugate base.
c) Strong base with weak acid. Insufficient reaction, so you will end up with both weak acid and conjugate base in solution. This results in a buffer.
d) Strong base with weak acid. Complete reaction, so no weak acid is left to make a buffer.

Answer 2

The first solution