Equal volumes of the following pairs of solutions are mixed. Which pair will be a buffer solution?
a) 0.10 M HBr and 0.05 M KOH
b) 0.10 M HBr and 0.15 M NH3
c) 0.10 M HBr and 0.05 M NH3
d) 0.10 M HBr and 0.20 M CH3 COOH
e) 0.10 M HBr and 0.20 M HCl
A buffer solution is made up of a weak acid and its conjugate base (or a weak base and its conjugate acid) and is able to resist changes in pH.
In this case, we need to identify the pair of solutions that contain a weak acid and its conjugate base.
a) HBr is a strong acid and KOH is a strong base, so this pair does not contain a weak acid and its conjugate base.
b) HBr is a strong acid and NH3 is a weak base, so this pair does not contain a weak acid and its conjugate base.
c) HBr is a strong acid and NH3 is a weak base, so this pair does not contain a weak acid and its conjugate base.
d) HBr is a strong acid and CH3COOH is a weak acid, so this pair contains a weak acid and its conjugate base.
e) HBr is a strong acid and HCl is a strong acid, so this pair does not contain a weak acid and its conjugate base.
Therefore, the pair that will be a buffer solution is d) 0.10 M HBr and 0.20 M CH3COOH.