In general chemistry, which statement best defines a buffer and its primary use?

• A. A buffer is a neutral salt solution and is used to set the pH permanently at $7$ regardless of what is added.
• B. A buffer is a solution with a very high concentration of a strong acid and is used to keep pH constant by overwhelming any added base.
• C. A buffer is a solution that rapidly reacts to eliminate all $H_{+}$ ions and is used to make solutions more acidic.
• D. A buffer is a solution that contains a weak acid and its conjugate base (or a weak base and its conjugate acid) and is used to resist changes in pH when small amounts of acid or base are added.

Answer: (D)

Verified step by step guidance

1. Understand that a buffer solution is designed to resist changes in pH when small amounts of acid or base are added, maintaining a relatively stable pH.
2. Recognize that buffers typically consist of a weak acid and its conjugate base, or a weak base and its conjugate acid, which work together to neutralize added H+ or OH- ions.
3. Recall that a neutral salt solution does not act as a buffer because it lacks the weak acid/base pair necessary to neutralize added acids or bases.
4. Note that a solution with a very high concentration of a strong acid is not a buffer because it cannot neutralize added base without a significant pH change.
5. Conclude that the best definition of a buffer is a solution containing a weak acid and its conjugate base (or a weak base and its conjugate acid) used to resist pH changes upon addition of small amounts of acid or base.