Which of the following solutions result in a buffer ?

Question

a) 0.100 L of 0.250 M CH3COOH + 0.050 L of 0.250 M NaOH


b) 0.100 L of 0.250 M CH3COOH + 0.050 L of 0.250 M HCl


c) 0.050 L of 0.250 M CH3COONa + 0.100 L of 0.250 M HCl


d) 0.100 L of 0.250 M CH3COONa + 0.050 L of 0.250 M HCl

Thanks in advance.

Answer 1

a) Because it results in a mix of CH3COOH + CH3COO-Na+
Adding a little OH- to such a solution increases the amount of CH3COO-Na+. Adding a bit of H+ increases the proportion of CH3COOH. So addition of strong H= or OH- (within reason) cannot move the pH much.

d) Because it results in a mix of CH3COOH and CH3COO-Na+ as before.

By contrast, b) gives a solution of CH3COOH and HCl, which cannot have buffer properties. c) gives a solution of CH3COOH only, which likewise has no buffer properties.