Unit 8: Topic 8 - Properties of Buffers

Question 1

Define what a buffer solution is and explain how it can withstand changes to pH when excess acid or base is added to the solution.

Answer 1

A buffer solution is a solution where a weak acid and its weak conjugate base, or vice versa, are both present. If a small amount of acid is added to this solution, the weak base will react with the acid; since the weak base is in excess, there are still significant amounts of weak acid and conjugate base, so the buffer is preserved and the pH changes only slightly. Similarly, the weak acid will react and neutralize strong bases that are added to the solution. This keeps the pH of the system relatively consistent.

Question 2

The following pairs of compounds exist in aqueous solution. Determine if they form a buffer solution.
1. HCl/Cl-
2. HF/F-
3. NH3/NH4+

Answer 2

Only 1 is not a buffer solution. In 2, HF is a weak acid and F- is the weak conjugate base. In 3, NH3 is the weak base and NH4+ is the weak conjugate acid. However, HCl is a strong acid, so Cl- isn’t basic. CI- won’t be able to neutralize any added acid.